Movatterモバイル変換

Network Working Group                                       J. RosenbergRequest for Comments: 3219                                   dynamicsoftCategory: Standards Track                                      H. Salama                                                           Cisco Systems                                                               M. Squire                                                       Hatteras Networks                                                            January 2002Telephony Routing over IP (TRIP)Status of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2002).  All Rights Reserved.Abstract   This document presents the Telephony Routing over IP (TRIP).  TRIP is   a policy driven inter-administrative domain protocol for advertising   the reachability of telephony destinations between location servers,   and for advertising attributes of the routes to those destinations.   TRIP's operation is independent of any signaling protocol, hence TRIP   can serve as the telephony routing protocol for any signaling   protocol.   The Border Gateway Protocol (BGP-4) is used to distribute routing   information between administrative domains.  TRIP is used to   distribute telephony routing information between telephony   administrative domains.  The similarity between the two protocols is   obvious, and hence TRIP is modeled after BGP-4.Table of Contents1    Terminology and Definitions  ..............................32    Introduction  .............................................43    Summary of Operation  .....................................53.1  Peering Session Establishment and Maintenance  ............53.2  Database Exchanges  .......................................63.3  Internal Versus External Synchronization  .................63.4  Advertising TRIP Routes  ..................................6Rosenberg, et. al.          Standards Track                     [Page 1]

RFC 3219            Telephony Routing over IP (TRIP)        January 20023.5  Telephony Routing Information Bases  ......................73.6  Routes in TRIP  ...........................................93.7  Aggregation  ..............................................94    Message Formats  ..........................................104.1  Message Header Format  ....................................104.2  OPEN Message Format  ......................................114.3  UPDATE Message Format  ....................................154.4  KEEPALIVE Message Format   ................................224.5  NOTIFICATION Message Format   .............................235    TRIP Attributes   .........................................245.1  WithdrawnRoutes  ..........................................245.2  ReachableRoutes  ..........................................285.3  NextHopServer   ...........................................295.4  AdvertisementPath   .......................................315.5  RoutedPath  ...............................................355.6  AtomicAggregate   .........................................365.7  LocalPreference   .........................................375.8  MultiExitDisc  ............................................385.9  Communities  ..............................................395.10 ITAD Topology    ..........................................415.11 ConvertedRoute  ...........................................435.12 Considerations for Defining New TRIP Attributes   .........446    TRIP Error Detection and Handling   .......................446.1  Message Header Error Detection and Handling   .............456.2  OPEN Message Error Detection and Handling   ...............456.3  UPDATE Message Error Detection and Handling   .............466.4  NOTIFICATION Message Error Detection and Handling   .......486.5  Hold Timer Expired Error Handling   .......................486.6  Finite State Machine Error Handling   .....................486.7  Cease   ...................................................486.8  Connection Collision Detection   ..........................487    TRIP Version Negotiation   ................................498    TRIP Capability Negotiation   .............................509    TRIP Finite State Machine   ...............................5010   UPDATE Message Handling   .................................5510.1 Flooding Process   ........................................5610.2 Decision Process   ........................................5810.3  Update-Send Process   .....................................6210.4  Route Selection Criteria   ................................6710.5  Originating TRIP Routes   .................................6711    TRIP Transport   ..........................................6812    ITAD Topology   ...........................................6813    IANA Considerations  ......................................6813.1  TRIP Capabilities   .......................................6813.2  TRIP Attributes    ........................................6913.3  Destination Address Families   ............................6913.4  TRIP Application Protocols   ..............................6913.5  ITAD Numbers   ............................................70Rosenberg, et. al.          Standards Track                     [Page 2]

RFC 3219            Telephony Routing over IP (TRIP)        January 200214    Security Considerations   .................................70   A1    Appendix 1: TRIP FSM State Transitions and Actions   ......71   A2    Appendix 2: Implementation Recommendations   ..............73   Acknowledgments  ................................................75   References  .....................................................75   Intellectual Property Notice  ...................................77   Authors' Addresses  .............................................78   Full Copyright Statement  .......................................791. Terminology and Definitions   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [1].   A framework for Telephony Routing over IP (TRIP) is described in [2].   We assume the reader is familiar with the framework and terminology   of [2].  We define and use the following terms in addition to those   defined in [2].   Telephony Routing Information Base (TRIB): The database of reachable   telephony destinations built and maintained at an LS as a result of   its participation in TRIP.   IP Telephony Administrative Domain (ITAD): The set of resources   (gateways, location servers, etc.) under the control of a single   administrative authority.  End users are customers of an ITAD.   Less/More Specific Route: A route X is said to be less specific than   a route Y if every destination in Y is also a destination in X, and X   and Y are not equal.  In this case, Y is also said to be more   specific than X.   Aggregation: Aggregation is the process by which multiple routes are   combined into a single less specific route that covers the same set   of destinations.  Aggregation is used to reduce the size of the TRIB   being synchronized with peer LSs by reducing the number of exported   TRIP routes.   Peers: Two LSs that share a logical association (a transport   connection).  If the LSs are in the same ITAD, they are internal   peers.  Otherwise, they are external peers.  The logical association   between two peer LSs is called a peering session.Rosenberg, et. al.          Standards Track                     [Page 3]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   Telephony Routing Information Protocol (TRIP): The protocol defined   in this specification.  The function of TRIP is to advertise the   reachability of telephony destinations, attributes associated with   the destinations, as well as the attributes of the path towards those   destinations.   TRIP destination: TRIP can be used to manage routing tables for   multiple protocols (SIP, H323, etc.).  In TRIP, a destination is the   combination of (a) a set of addresses (given by an address family and   address prefix), and (b) an application protocol (SIP, H323, etc).2. Introduction   The gateway location and routing problem has been introduced in [2].   It is considered one of the more difficult problems in IP telephony.   The selection of an egress gateway for a telephony call, traversing   an IP network towards an ultimate destination in the PSTN, is driven   in large part by the policies of the various parties along the path,   and by the relationships established between these parties.  As such,   a global directory of egress gateways in which users look up   destination phone numbers is not a feasible solution.  Rather,   information about the availability of egress gateways is exchanged   between providers, and subject to policy, made available locally and   then propagated to other providers in other ITADs, thus creating   routes towards these egress gateways.  This would allow each provider   to create its own database of reachable phone numbers and the   associated routes - such a database could be very different for each   provider depending on policy.   TRIP is an inter-domain (i.e., inter-ITAD) gateway location and   routing protocol.  The primary function of a TRIP speaker, called a   location server (LS), is to exchange information with other LSs.   This information includes the reachability of telephony destinations,   the routes towards these destinations, and information about gateways   towards those telephony destinations residing in the PSTN.  The TRIP   requirements are set forth in [2].   LSs exchange sufficient routing information to construct a graph of   ITAD connectivity so that routing loops may be prevented.  In   addition, TRIP can be used to exchange attributes necessary to   enforce policies and to select routes based on path or gateway   characteristics.  This specification defines TRIP's transport and   synchronization mechanisms, its finite state machine, and the TRIP   data.  This specification defines the basic attributes of TRIP.  The   TRIP attribute set is extendible, so additional attributes may be   defined in future documents.Rosenberg, et. al.          Standards Track                     [Page 4]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   TRIP is modeled after the Border Gateway Protocol 4 (BGP-4) [3] and   enhanced with some link state features, as in the Open Shortest Path   First (OSPF) protocol [4], IS-IS [5], and the Server Cache   Synchronization Protocol (SCSP) [6].  TRIP uses BGP's inter-domain   transport mechanism, BGP's peer communication, BGP's finite state   machine, and similar formats and attributes as BGP.  Unlike BGP   however, TRIP permits generic intra-domain LS topologies, which   simplifies configuration and increases scalability in contrast to   BGP's full mesh requirement of internal BGP speakers.  TRIP uses an   intra-domain flooding mechanism similar to that used in OSPF [4],   IS-IS [5], and SCSP [6].   TRIP permits aggregation of routes as they are advertised through the   network.  TRIP does not define a specific route selection algorithm.   TRIP runs over a reliable transport protocol.  This eliminates the   need to implement explicit fragmentation, retransmission,   acknowledgment, and sequencing.  The error notification mechanism   used in TRIP assumes that the transport protocol supports a graceful   close, i.e., that all outstanding data will be delivered before the   connection is closed.   TRIP's operation is independent of any particular telephony signaling   protocol.  Therefore, TRIP can be used as the routing protocol for   any of these protocols, e.g., H.323 [7] and SIP [8].   The LS peering topology is independent of the physical topology of   the network.  In addition, the boundaries of an ITAD are independent   of the boundaries of the layer 3 routing autonomous systems.  Neither   internal nor external TRIP peers need to be physically adjacent.3. Summary of Operation   This section summarizes the operation of TRIP.  Details are provided   in later sections.3.1. Peering Session Establishment and Maintenance   Two peer LSs form a transport protocol connection between one   another.  They exchange messages to open and confirm the connection   parameters, and to negotiate the capabilities of each LS as well as   the type of information to be advertised over this connection.   KeepAlive messages are sent periodically to ensure adjacent peers are   operational.  Notification messages are sent in response to errors or   special conditions.  If a connection encounters an error condition, a   Notification message is sent and the connection is closed.Rosenberg, et. al.          Standards Track                     [Page 5]

RFC 3219            Telephony Routing over IP (TRIP)        January 20023.2. Database Exchanges   Once the peer connection has been established, the initial data flow   is a dump of all routes relevant to the new peer (In the case of an   external peer, all routes in the LS's Adj-TRIB-Out for that external   peer.  In the case of an internal peer, all routes in the Ext-TRIB   and all Adj-TRIBs-In).  Note that the different TRIBs are defined inSection 3.5.   Incremental updates are sent as the TRIP routing tables (TRIBs)   change.  TRIP does not require periodic refresh of the routes.   Therefore, an LS must retain the current version of all routing   entries.   If a particular ITAD has multiple LSs and is providing transit   service for other ITADs, then care must be taken to ensure a   consistent view of routing within the ITAD.  When synchronized the   TRIP routing tables, i.e., the Loc-TRIBs, of all internal peers are   identical.3.3. Internal Versus External Synchronization   As with BGP, TRIP distinguishes between internal and external peers.   Within an ITAD, internal TRIP uses link-state mechanisms to flood   database updates over an arbitrary topology.  Externally, TRIP uses   point-to-point peering relationships to exchange database   information.   To achieve internal synchronization, internal peer connections are   configured between LSs of the same ITAD such that the resulting   intra-domain LS topology is connected and sufficiently redundant.   This is different from BGP's approach that requires all internal   peers to be connected in a full mesh topology, which may result in   scaling problems.  When an update is received from an internal peer,   the routes in the update are checked to determine if they are newer   than the version already in the database.  Newer routes are then   flooded to all other peers in the same domain.3.4. Advertising TRIP Routes   In TRIP, a route is defined as the combination of (a) a set of   destination addresses (given by an address family indicator and an   address prefix), and (b) an application protocol (e.g. SIP, H323,   etc.).  Generally, there are additional attributes associated with   each route (for example, the next-hop server).Rosenberg, et. al.          Standards Track                     [Page 6]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   TRIP routes are advertised between a pair of LSs in UPDATE messages.   The destination addresses are included in the ReachableRoutes   attribute of the UPDATE, while other attributes describe things like   the path or egress gateway.   If an LS chooses to advertise a TRIP route, it may add to or modify   the attributes of the route before advertising it to a peer.  TRIP   provides mechanisms by which an LS can inform its peer that a   previously advertised route is no longer available for use.  There   are three methods by which a given LS can indicate that a route has   been withdrawn from service:      -  Include the route in the WithdrawnRoutes Attribute in an UPDATE         message, thus marking the associated destinations as being no         longer available for use.      -  Advertise a replacement route with the same set of destinations         in the ReachableRoutes Attribute.      -  For external peers where flooding is not in use, the LS-to-LS         peer connection can be closed, which implicitly removes from         service all routes which the pair of LSs had advertised to each         other over that peer session.  Note that terminating an         internal peering session does not necessarily remove the routes         advertised by the peer LS as the same routes may have been         received from multiple internal peers because of flooding.  If         an LS determines that another internal LS is no longer active         (from the ITAD Topology attributes of the UPDATE messages from         other internal peers), then it MUST remove all routes         originated into the LS by that LS and rerun its decision         process.3.5. Telephony Routing Information Bases   A TRIP LS processes three types of routes:      -  External routes: An external route is a route received from an         external peer LS      -  Internal routes: An internal route is a route received from an         internal LS in the same ITAD.      -  Local routes: A local route is a route locally injected into         TRIP, e.g. by configuration or by route redistribution from         another routing protocol.   The Telephony Routing Information Base (TRIB) within an LS consists   of four distinct parts:Rosenberg, et. al.          Standards Track                     [Page 7]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002      -  Adj-TRIBs-In: The Adj-TRIBs-In store routing information that         has been learned from inbound UPDATE messages.  Their contents         represent TRIP routes that are available as an input to the         Decision Process.  These are the "unprocessed" routes received.         The routes from each external peer LS and each internal LS are         maintained in this database independently, so that updates from         one peer do not affect the routes received from another LS.         Note that there is an Adj-TRIB-In for every LS within the         domain, even those with which the LS is not directly peered.      -  Ext-TRIB: There is only one Ext-TRIB database per LS.  The LS         runs the route selection algorithm on all external routes         (stored in the Adj-TRIBs-In of the external peers) and local         routes (may be stored in an Adj-TRIB-In representing the local         LS) and selects the best route for a given destination and         stores it in the Ext-TRIB.  The use of Ext-TRIB will be         explained further inSection 10.3.1      -  Loc-TRIB: The Loc-TRIB contains the local TRIP routing         information that the LS has selected by applying its local         policies to the routing information contained in its Adj-         TRIBs-In of internal LSs and the Ext-TRIB.      -  Adj-TRIBs-Out:  The Adj-TRIBs-Out store the information that         the local LS has selected for advertisement to its external         peers.  The routing information stored in the Adj-TRIBs-Out         will be carried in the local LS's UPDATE messages and         advertised to its peers.   Figure 1 illustrates the relationship between the four parts of the   routing information base.                            Loc-TRIB                                ^                                |                        Decision Process                         ^      ^      |                         |      |      |                Adj-TRIBs-In    |      V               (Internal LSs)   |   Adj-TRIBs-Out                                |                                |                                |                             Ext-TRIB                            ^        ^                            |        |                   Adj-TRIB-In      Local Routes               (External Peers)                     Figure 1: TRIB RelationshipsRosenberg, et. al.          Standards Track                     [Page 8]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   Although the conceptual model distinguishes between Adj-TRIBs-In,   Ext-TRIB, Loc-TRIB, and Adj-TRIBs-Out, this neither implies nor   requires that an implementation must maintain four separate copies of   the routing information.  The choice of implementation (for example,   4 copies of the information vs. 1 copy with pointers) is not   constrained by the protocol.3.6. Routes in TRIP   A route in TRIP specifies a range of numbers by being a prefix of   those numbers (the exact definition & syntax of route are in 5.1.1).   Arbitrary ranges of numbers are not atomically representable by a   route in TRIP.  A prefix range is the only type of range supported   atomically.  An arbitrary range can be accomplished by using multiple   prefixes in a ReachableRoutes attribute (seeSection 5.1 & 5.2).  For   example, 222-xxxx thru 999-xxxx could be represented by including the   prefixes 222, 223, 224,...,23,24,...,3,4,...,9 in a ReachableRoutes   attribute.3.7. Aggregation   Aggregation is a scaling enhancement used by an LS to reduce the   number of routing entries that it has to synchronize with its peers.   Aggregation may be performed by an LS when there is a set of routes   {R1, R2, ...} in its TRIB such that there exists a less specific   route R where every valid destination in R is also a valid   destination in {R1, R2, ...} and vice-versa.Section 5 includes a   description of how to combine each attribute (by type) on the {R1,   R2, ...} routes into an attribute for R.   Note that there is no mechanism within TRIP to communicate that a   particular address prefix is not used or valid within a particular   address family, and thus that these addresses could be skipped during   aggregation.  LSs may use methods outside of TRIP to learn of invalid   prefixes that may be ignored during aggregation.   An LS is not required to perform aggregation, however it is   recommended whenever maintaining a smaller TRIB is important.  An LS   decides based on its local policy whether or not to aggregate a set   of routes into a single aggregate route.   Whenever an LS aggregates multiple routes where the NextHopServer is   not identical in all aggregated routes, the NextHopServer attribute   of the aggregate route must be set to a signalling server in the   aggregating LS's domain.Rosenberg, et. al.          Standards Track                     [Page 9]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   When an LS resets the NextHopServer of any route, and this may be   performed because of aggregation or other reasons, it has the effect   of adding another signalling server along the signalling path to   these destinations.  The end result is that the signalling path   between two destinations may consist of multiple signalling servers   across multiple domains.4. Message Formats   This section describes message formats used by TRIP.  Messages are   sent over a reliable transport protocol connection.  A message MUST   be processed only after it is entirely received.  The maximum message   size is 4096 octets.  All implementations MUST support this maximum   message size.  The smallest message that MAY be sent consists of a   TRIP header without a data portion, or 3 octets.4.1. Message Header Format   Each message has a fixed-size header.  There may or may not be a data   portion following the header, depending on the message type.  The   layout of the header fields is shown in Figure 2.         0                   1                   2         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3         +--------------+----------------+---------------+         |          Length               |      Type     |         +--------------+----------------+---------------+                      Figure 2: TRIP Header   Length:  This 2-octet unsigned integer indicates the total length of   the message, including the header, in octets.  Thus, it allows one to   locate, in the transport-level stream, the beginning of the next   message.  The value of the Length field must always be at least 3 and   no greater than 4096, and may be further constrained depending on the   message type.  No padding of extra data after the message is allowed,   so the Length field must have the smallest value possible given the   rest of the message.   Type:  This 1-octet unsigned integer indicates the type code of the   message.  The following type codes are defined:      1 - OPEN      2 - UPDATE      3 - NOTIFICATION      4 - KEEPALIVERosenberg, et. al.          Standards Track                    [Page 10]

RFC 3219            Telephony Routing over IP (TRIP)        January 20024.2. OPEN Message Format   After a transport protocol connection is established, the first   message sent by each side is an OPEN message.  If the OPEN message is   acceptable, a KEEPALIVE message confirming the OPEN is sent back.   Once the OPEN is confirmed, UPDATE, KEEPALIVE, and NOTIFICATION   messages may be exchanged.   The minimum length of the OPEN message is 17 octets (including   message header).  OPEN messages not meeting this minimum requirement   are handled as defined inSection 6.2.   In addition to the fixed-size TRIP header, the OPEN message contains   the following fields:       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +---------------+---------------+--------------+----------------+      |    Version    |    Reserved   |          Hold Time            |      +---------------+---------------+--------------+----------------+      |                            My ITAD                            |      +---------------+---------------+--------------+----------------+      |                        TRIP Identifier                        |      +---------------+---------------+--------------+----------------+      |    Optional Parameters Len    |Optional Parameters (variable)...      +---------------+---------------+--------------+----------------+                        Figure 3: TRIP OPEN Header   Version:   This 1-octet unsigned integer indicates the protocol version of the   message.  The current TRIP version number is 1.   Hold Time:   This 2-octet unsigned integer indicates the number of seconds that   the sender proposes for the value of the Hold Timer.  Upon receipt of   an OPEN message, an LS MUST calculate the value of the Hold Timer by   using the smaller of its configured Hold Time and the Hold Time   received in the OPEN message.  The Hold Time MUST be either zero or   at least three seconds.  An implementation MAY reject connections on   the basis of the Hold Time.  The calculated value indicates the   maximum number of seconds that may elapse between the receipt of   successive KEEPALIVE and/or UPDATE messages by the sender.   This 4-octet unsigned integer indicates the ITAD number of the   sender.  The ITAD number must be unique for this domain within this   confederation of cooperating LSs.Rosenberg, et. al.          Standards Track                    [Page 11]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   ITAD numbers are assigned by IANA as specified inSection 13.  This   document reserves ITAD number 0.  ITAD numbers from 1 to 255 are   designated for private use.   TRIP Identifier:   This 4-octet unsigned integer indicates the TRIP Identifier of the   sender.  The TRIP Identifier MUST uniquely identify this LS within   its ITAD.  A given LS MAY set the value of its TRIP Identifier to an   IPv4 address assigned to that LS.  The value of the TRIP Identifier   is determined on startup and MUST be the same for all peer   connections.  When comparing two TRIP identifiers, the TRIP   Identifier is interpreted as a numerical 4-octet unsigned integer.   Optional Parameters Length:   This 2-octet unsigned integer indicates the total length of the   Optional Parameters field in octets.  If the value of this field is   zero, no Optional Parameters are present.   Optional Parameters:   This field may contain a list of optional parameters, where each   parameter is encoded as a <Parameter Type, Parameter Length,   Parameter Value> triplet.       0                   1                   2       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +---------------+---------------+--------------+----------------+      |       Parameter Type          |       Parameter Length        |      +---------------+---------------+--------------+----------------+      |                  Parameter Value (variable)...      +---------------+---------------+--------------+----------------+                    Figure 4: Optional Parameter Encoding   Parameter Type:   This is a 2-octet field that unambiguously identifies individual   parameters.   Parameter Length:   This is a 2-octet field that contains the length of the Parameter   Value field in octets.   Parameter Value:   This is a variable length field that is interpreted according to the   value of the Parameter Type field.Rosenberg, et. al.          Standards Track                    [Page 12]

RFC 3219            Telephony Routing over IP (TRIP)        January 20024.2.1. Open Message Optional Parameters   This document defines the following Optional Parameters for the OPEN   message.4.2.1.1. Capability Information   Capability Information uses Optional Parameter type 1.  This is an   optional parameter used by an LS to convey to its peer the list of   capabilities supported by the LS.  This permits an LS to learn of the   capabilities of its peer LSs.  Capability negotiation is defined inSection 8.   The parameter contains one or more triples <Capability Code,   Capability Length, Capability Value>, where each triple is encoded as   shown below:    0                   1                   2    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +---------------+---------------+--------------+----------------+   |       Capability Code         |       Capability Length       |   +---------------+---------------+--------------+----------------+   |       Capability Value (variable)...   +---------------+---------------+--------------+----------------+           Figure 5:  Capability Optional Parameter   Capability Code:   Capability Code is a 2-octet field that unambiguously identifies   individual capabilities.   Capability Length:   Capability Length is a 2-octet field that contains the length of the   Capability Value field in octets.   Capability Value:   Capability Value is a variable length field that is interpreted   according to the value of the Capability Code field.   Any particular capability, as identified by its Capability Code, may   appear more than once within the Optional Parameter.   This document reserves Capability Codes 32768-65535 for vendor-   specific applications (these are the codes with the first bit of the   code value equal to 1).  This document reserves value 0.  Capability   Codes (other than those reserved for vendor specific use) are   controlled by IANA.  SeeSection 13 for IANA considerations.Rosenberg, et. al.          Standards Track                    [Page 13]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   The following Capability Codes are defined by this specification:      Code           Capability      1              Route Types Supported      2              Send Receive Capability4.2.1.1.1. Route Types Supported   The Route Types Supported Capability Code lists the route types   supported in this peering session by the transmitting LS.  An LS MUST   NOT use route types that are not supported by the peer LS in any   particular peering session.  If the route types supported by a peer   are not satisfactory, an LS SHOULD terminate the peering session.   The format for a Route Type is:    0                   1                   2    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +---------------+---------------+--------------+----------------+   |        Address Family         |     Application Protocol      |   +---------------+---------------+--------------+----------------+            Figure 6: Route Types Supported Capability   The Address Family and Application Protocol are as defined inSection5.1.1.  Address Family gives the address family being routed (within   the ReachableRoutes attribute).  The application protocol lists the   application for which the routes apply.  As an example, a route type   for TRIP could be <E.164, SIP>, indicating a set of E.164   destinations for the SIP protocol.   The Route Types Supported Capability MAY contain multiple route types   in the capability.  The number of route types within the capability   is the maximum number that can fit given the capability length.  The   Capability Code is 1 and the length is variable.4.2.1.1.2. Send Receive Capability   This capability specifies the mode in which the LS will operate with   this particular peer.  The possible modes are: Send Only mode,   Receive Only mode, or Send Receive mode.  The default mode is Send   Receive mode.   In Send Only mode, an LS transmits UPDATE messages to its peer, but   the peer MUST NOT transmit UPDATE messages to that LS.  If an LS in   Send Only mode receives an UPDATE message from its peer, it MUST   discard that message, but no further action should be taken.Rosenberg, et. al.          Standards Track                    [Page 14]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   The UPDATE messages sent by an LS in Send Only mode to its intra-   domain peer MUST include the ITAD Topology attribute whenever the   topology changes.  A useful application of an LS in Send Only mode   with an external peer is to enable gateway registration services.   If a service provider terminates calls to a set of gateways it owns,   but never initiates calls, it can set its LSs to operate in Send Only   mode, since they only ever need to generate UPDATE messages, not   receive them.  If an LS in Send Receive mode has a peering session   with a peer in Send Only mode, that LS MUST set its route   dissemination policy such that it does not send any UPDATE messages   to its peer.   In Receive Only mode, the LS acts as a passive TRIP listener.  It   receives and processes UPDATE messages from its peer, but it MUST NOT   transmit any UPDATE messages to its peer.  This is useful for   management stations that wish to collect topology information for   display purposes.   The behavior of an LS in Send Receive mode is the default TRIP   operation specified throughout this document.   The Send Receive capability is a 4-octet unsigned numeric value.  It   can only take one of the following three values:      1 - Send Receive mode      2 - Send only mode      3 - Receive Only mode   A peering session MUST NOT be established between two LSs if both of   them are  in Send Only mode or if both of them are in Receive Only   mode.  If a peer LS detects such a capability mismatch when   processing an OPEN message, it MUST respond with a NOTIFICATION   message and close the peer session.  The error code in the   NOTIFICATION message must be set to "Capability Mismatch."   An LS MUST be configured in the same Send Receive mode for all peers.4.3. UPDATE Message Format   UPDATE messages are used to transfer routing information between LSs.   The information in the UPDATE packet can be used to construct a graph   describing the relationships between the various ITADs.  By applying   rules to be discussed, routing information loops and some other   anomalies can be prevented.Rosenberg, et. al.          Standards Track                    [Page 15]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   An UPDATE message is used to both advertise and withdraw routes from   service.  An UPDATE message may simultaneously advertise and withdraw   TRIP routes.   In addition to the TRIP header, the TRIP UPDATE contains a list of   routing attributes as shown in Figure 7.  There is no padding between   routing attributes.         +------------------------------------------------+--...         | First Route Attribute | Second Route Attribute |  ...         +------------------------------------------------+--...                    Figure 7: TRIP UPDATE Format   The minimum length of an UPDATE message is 3 octets (there are no   mandatory attributes in TRIP).4.3.1. Routing Attributes   A variable length sequence of routing attributes is present in every   UPDATE message.  Each attribute is a triple <attribute type,   attribute length, attribute value> of variable length.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +---------------+---------------+--------------+----------------+      |  Attr. Flags  |Attr. Type Code|         Attr. Length          |      +---------------+---------------+--------------+----------------+      |                   Attribute Value (variable)                  |      +---------------+---------------+--------------+----------------+                    Figure 8: Routing Attribute Format   Attribute Type is a two-octet field that consists of the Attribute   Flags octet followed by the Attribute Type Code octet.   The Attribute Type Code defines the type of attribute.  The basic   TRIP-defined Attribute Type Codes are discussed later in this   section.  Attributes MUST appear in the UPDATE message in numerical   order of the Attribute Type Code.  An attribute MUST NOT be included   more than once in the same UPDATE message.  Attribute Flags are used   to control attribute processing when the attribute type is unknown.   Attribute Flags are further defined inSection 4.3.2.Rosenberg, et. al.          Standards Track                    [Page 16]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   This document reserves Attribute Type Codes 224-255 for vendor-   specific applications (these are the codes with the first three bits   of the code equal to 1).  This document reserves value 0.  Attribute   Type Codes (other than those reserved for vendor specific use) are   controlled by IANA.  SeeSection 13 for IANA considerations.   The third and the fourth octets of the route attribute contain the   length of the attribute value field in octets.   The remaining octets of the attribute represent the Attribute Value   and are interpreted according to the Attribute Flags and the   Attribute Type Code.  The basic supported attribute types, their   values, and their uses are defined in this specification.  These are   the attributes necessary for proper loop free operation of TRIP, both   inter-domain and intra-domain.  Additional attributes may be defined   in future documents.4.3.2. Attribute Flags   It is clear that the set of attributes for TRIP will evolve over   time.  Hence it is essential that mechanisms be provided to handle   attributes with unrecognized types.  The handling of unrecognized   attributes is controlled via the flags field of the attribute.   Recognized attributes should be processed according to their specific   definition.   The following are the attribute flags defined by this specification:            Bit       Flag            0         Well-Known Flag            1         Transitive Flag            2         Dependent Flag            3         Partial Flag            4         Link-state Encapsulated Flag   The high-order bit (bit 0) of the Attribute Flags octet is the Well-   Known Bit.  It defines whether the attribute is not well-known (if   set to 1) or well-known (if set to 0).  Implementations are not   required to support not well-known attributes, but MUST support   well-known attributes.   The second high-order bit (bit 1) of the Attribute Flags octet is the   Transitive bit.  It defines whether a not well-known attribute is   transitive (if set to 1) or non-transitive (if set to 0).  For well-   known attributes, the Transitive bit MUST be zero on transmit and   MUST be ignored on receipt.   The third high-order bit (bit 2) of the Attribute Flags octet is the   Dependent bit.  It defines whether a transitive attribute isRosenberg, et. al.          Standards Track                    [Page 17]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   dependent (if set to 1) or independent (if set to 0).  For well-known   attributes and for non-transitive attributes, the Dependent bit is   irrelevant, and MUST be set to zero on transmit and MUST be ignored   on receipt.   The fourth high-order bit (bit 3) of the Attribute Flags octet is the   Partial bit.  It defines whether the information contained in the not   well-known transitive attribute is partial (if set to 1) or complete   (if set to 0).  For well-known attributes and for non-transitive   attributes the Partial bit MUST be set to 0 on transmit and MUST be   ignored on receipt.   The fifth high-order bit (bit 4) of the Attribute Flags octet is the   Link-state Encapsulation bit.  This bit is only applicable to certain   attributes (ReachableRoutes and WithdrawnRoutes) and determines the   encapsulation of the routes within those attributes.  If this bit is   set, link-state encapsulation is used within the attribute.   Otherwise, standard encapsulation is used within the attribute.  The   Link-state Encapsulation technique is described inSection 4.3.2.4.   This flag is only valid on the ReachableRoutes and WithdrawnRoutes   attributes.  It MUST be cleared on transmit and MUST be ignored on   receipt for all other attributes.   The other bits of the Attribute Flags octet are unused.  They MUST be   zeroed on transmit and ignored on receipt.4.3.2.1. Attribute Flags and Route Selection   Any recognized attribute can be used as input to the route selection   process, although the utility of some attributes in route selection   is minimal.4.3.2.2. Attribute Flags and Route Dissemination   TRIP provides for two variations of transitivity due to the fact that   intermediate LSs need not modify the NextHopServer when propagating   routes.  Attributes may be non-transitive, dependent transitive, or   independent transitive.  An attribute cannot be both dependent   transitive and independent transitive.   Unrecognized independent transitive attributes may be propagated by   any intermediate LS.  Unrecognized dependent transitive attributes   MAY only be propagated if the LS is NOT changing the next-hop server.   The transitivity variations permit some unrecognized attributes to be   carried end-to-end (independent transitive), some to be carried   between adjacent next-hop servers (dependent transitive), and other   to be restricted to peer LSs (non-transitive).Rosenberg, et. al.          Standards Track                    [Page 18]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   An LS that passes an unrecognized transitive attribute to a peer MUST   set the Partial flag on that attribute.  Any LS along a path MAY   insert a transitive attribute into a route.  If any LS except the   originating LS inserts a new independent transitive attribute into a   route, then it MUST set the Partial flag on that attribute.  If any   LS except an LS that modifies the NextHopServer inserts a new   dependent transitive attribute into a route, then it MUST set the   Partial flag on that attribute.  The Partial flag indicates that not   every LS along the relevant path has processed and understood the   attribute.  For independent transitive attributes, the "relevant   path" is the path given in the AdvertisementPath attribute.  For   dependent transitive attributes, the relevant path consists only of   those domains thru which this object has passed since the   NextHopServer was last modified.  The Partial flag in an independent   transitive attribute MUST NOT be unset by any other LS along the   path.  The Partial flag in a dependent transitive attribute MUST be   reset whenever the NextHopServer is changed, but MUST NOT be unset by   any LS that is not changing the NextHopServer.   The rules governing the addition of new non-transitive attributes are   defined independently for each non-transitive attribute.  Any   attribute MAY be updated by an LS in the path.4.3.2.3. Attribute Flags and Route Aggregation   Each attribute defines how it is to be handled during route   aggregation.   The rules governing the handling of unknown attributes are guided by   the Attribute Flags.  Unrecognized transitive attributes are dropped   during aggregation.  There should be no unrecognized non-transitive   attributes during aggregation because non-transitive attributes must   be processed by the local LS in order to be propagated.4.3.2.4. Attribute Flags and Encapsulation   Normally attributes have the simple format as described inSection4.3.1.  If the Link-state Encapsulation Flag is set, then the two   additional fields are added to the attribute header as shown in   Figure 9.Rosenberg, et. al.          Standards Track                    [Page 19]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002    0                   1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +---------------+---------------+--------------+----------------+   |  Attr. Flags  |Attr. Type Code|          Attr. Length         |   +---------------+---------------+--------------+----------------+   |                  Originator TRIP Identifier                   |   +---------------+---------------+--------------+----------------+   |                        Sequence Number                        |   +---------------+---------------+--------------+----------------+   |                   Attribute Value (variable)                  |   +---------------+---------------+--------------+----------------+                 Figure 9: Link State Encapsulation   The Originator TRIP ID and Sequence Number are used to control the   flooding of routing updates within a collection of servers.  These   fields are used to detect duplicate and old routes so that they are   not further propagated to other LSs.  The use of these fields is   defined inSection 10.1.4.3.3. Mandatory Attributes   There are no Mandatory attributes in TRIP.  However, there are   Conditional Mandatory attributes.  A conditional mandatory attribute   is an attribute, which MUST be included in an UPDATE message if   another attribute is included in that message.  For example, if an   UPDATE message includes a ReachableRoutes attribute, it MUST include   an AdvertisementPath attribute as well.   The three base attributes in TRIP are WithdrawnRoutes,   ReachableRoutes, and ITAD Topology.  Their presence in an UPDATE   message is entirely optional and independent of any other attributes.4.3.4. TRIP UPDATE Attributes   This section summarizes the attributes that may be carried in an   UPDATE message.  Attributes MUST appear in the UPDATE message in   increasing order of the Attribute Type Code.  Additional details are   provided inSection 5.4.3.4.1. WithdrawnRoutes   This attribute lists a set of routes that are being withdrawn from   service.  The transmitting LS has determined that these routes should   no longer be advertised, and is propagating this information to its   peers.Rosenberg, et. al.          Standards Track                    [Page 20]

RFC 3219            Telephony Routing over IP (TRIP)        January 20024.3.4.2. ReachableRoutes   This attribute lists a set of routes that are being added to service.   These routes will have the potential to be inserted into the Adj-   TRIBs-In of the receiving LS and the route selection process will be   applied to them.4.3.4.3. NextHopServer   This attribute gives the identity of the entity to which messages   should be sent along this routed path.  It specifies the identity of   the next hop server as either a host domain name or an IP address.   It MAY optionally specify the UDP/TCP port number for the next hop   signaling server.  If not specified, then the default port SHOULD be   used.  The NextHopServer is specific to the set of destinations and   application protocol defined in the ReachableRoutes attribute.  Note   that this is NOT necessarily the address to which media (voice,   video, etc.)  should be transmitted, it is only for the application   protocol as given in the ReachableRoutes attribute.4.3.4.4. AdvertisementPath   The AdvertisementPath is analogous to the AS_PATH in BGP4 [3].  The   attribute records the sequence of domains through which this   advertisement has passed.  The attribute is used to detect when the   routing advertisement is looping.  This attribute does NOT reflect   the path through which messages following this route would traverse.   Since the next-hop need not be modified by each LS, the actual path   to the destination might not have to traverse every domain in the   AdvertisementPath.4.3.4.5. RoutedPath   The RoutedPath attribute is analogous to the AdvertisementPath   attribute, except that it records the actual path (given by the list   of domains) *to* the destinations.  Unlike AdvertisementPath, which   is modified each time the route is propagated, RoutedPath is only   modified when the NextHopServer attribute changes.  Thus, it records   the subset of the AdvertisementPath which signaling messages   following this particular route would traverse.4.3.4.6. AtomicAggregate   The AtomicAggregate attribute indicates that a route may actually   include domains not listed in the RoutedPath.  If an LS, when   presented with a set of overlapping routes from a peer LS, selects a   less specific route without selecting the more specific route, then   the LS MUST include the AtomicAggregate attribute with the route.  AnRosenberg, et. al.          Standards Track                    [Page 21]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   LS receiving a route with an AtomicAggregate attribute MUST NOT make   the set of destinations more specific when advertising it to other   LSs.4.3.4.7. LocalPreference   The LocalPreference attribute is an intra-domain attribute used to   inform other LSs of the local LS's preference for a given route.  The   preference of a route is calculated at the ingress to a domain and   passed as an attribute with that route throughout the domain.  Other   LSs within the same ITAD use this attribute in their route selection   process.  This attribute has no significance between domains.4.3.4.8. MultiExitDisc   There may be more than one LS peering relationship between   neighboring domains.  The MultiExitDisc attribute is used by an LS to   express a preference for one link between the domains over another   link between the domains.  The use of the MultiExitDisc attribute is   controlled by local policy.4.3.4.9. Communities   The Communities attribute is not a well-known attribute.  It is used   to facilitate and simplify the control of routing information by   grouping destinations into communities.4.3.4.10. ITAD Topology   The ITAD topology attribute is an intra-domain attribute that is used   by LSs to indicate their intra-domain topology to other LSs in the   domain.4.3.4.11. ConvertedRoute   The ConvertedRoute attribute indicates that an intermediate LS has   altered the route by changing the route's Application Protocol.4.4. KEEPALIVE Message Format   TRIP does not use any transport-based keep-alive mechanism to   determine if peers are reachable.  Instead, KEEPALIVE messages are   exchanged between peers often enough as not to cause the Hold Timer   to expire.  A reasonable maximum time between KEEPALIVE messages   would be one third of the Hold Time interval.  KEEPALIVE messages   MUST NOT be sent more than once every 3 seconds.  An implementation   SHOULD adjust the rate at which it sends KEEPALIVE messages as a   function of the negotiated Hold Time interval.Rosenberg, et. al.          Standards Track                    [Page 22]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   If the negotiated Hold Time interval is zero, then periodic KEEPALIVE   messages MUST NOT be sent.   The KEEPALIVE message consists of only a message header and has a   length of 3 octets.4.5. NOTIFICATION Message Format   A NOTIFICATION message is sent when an error condition is detected.   The TRIP transport connection is closed immediately after sending a   NOTIFICATION message.   In addition to the fixed-size TRIP header, the NOTIFICATION message   contains the following fields:    0                   1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +---------------+---------------+--------------+----------------+   |  Error Code   | Error Subcode |       Data... (variable)   +---------------+---------------+--------------+----------------+                Figure 10: TRIP NOTIFICATION Format   Error Code:   This 1-octet unsigned integer indicates the type of NOTIFICATION.   The following Error Codes have been defined:   Error Code       Symbolic Name               Reference     1         Message Header ErrorSection 6.1     2         OPEN Message ErrorSection 6.2     3         UPDATE Message ErrorSection 6.3     4         Hold Timer ExpiredSection 6.5     5         Finite State Machine ErrorSection 6.6     6         CeaseSection 6.7   Error Subcode:   This 1-octet unsigned integer provides more specific information   about the nature of the reported error.  Each Error Code may have one   or more Error Subcodes associated with it.  If no appropriate Error   Subcode is defined, then a zero (Unspecific) value is used for the   Error Subcode field.   Message Header Error Subcodes:      1  - Bad Message Length.      2  - Bad Message Type.Rosenberg, et. al.          Standards Track                    [Page 23]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   OPEN Message Error Subcodes:      1  - Unsupported Version Number.      2  - Bad Peer ITAD.      3  - Bad TRIP Identifier.      4  - Unsupported Optional Parameter.      5  - Unacceptable Hold Time.      6  - Unsupported Capability.      7  - Capability Mismatch.   UPDATE Message Error Subcodes:      1 - Malformed Attribute List.      2 - Unrecognized Well-known Attribute.      3 - Missing Well-known Mandatory Attribute.      4 - Attribute Flags Error.      5 - Attribute Length Error.      6 - Invalid Attribute.   Data:   This variable-length field is used to diagnose the reason for the   NOTIFICATION.  The contents of the Data field depend upon the Error   Code and Error Subcode.   Note that the length of the data can be determined from the message   length field by the formula:            Data Length = Message Length - 5   The minimum length of the NOTIFICATION message is 5 octets (including   message header).5. TRIP Attributes   This section provides details on the syntax and semantics of each   TRIP UPDATE attribute.5.1. WithdrawnRoutes   Conditional Mandatory: False.   Required Flags: Well-known.   Potential Flags: Link-State Encapsulation (when flooding).   TRIP Type Code: 1   The WithdrawnRoutes specifies a set of routes that are to be removed   from service by the receiving LS(s).  The set of routes MAY be empty,   indicated by a length field of zero.Rosenberg, et. al.          Standards Track                    [Page 24]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.1.1. Syntax of WithdrawnRoutes   The WithdrawnRoutes Attribute encodes a sequence of routes in its   value field.  The format for individual routes is given inSection5.1.1.1.  The WithdrawnRoutes Attribute lists the individual routes   sequentially with no padding as shown in Figure 11.  Each route   includes a length field so that the individual routes within the   attribute can be delineated.            +---------------------+---------------------+...            |  WithdrawnRoute1... |  WithdrawnRoute2... |...            +---------------------+---------------------+...                 Figure 11: WithdrawnRoutes Format5.1.1.1. Generic TRIP Route Format   The generic format for a TRIP route is given in Figure 12.    0                   1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +---------------+---------------+--------------+----------------+   |       Address Family          |      Application Protocol     |   +---------------+---------------+--------------+----------------+   |            Length             |       Address (variable)     ...   +---------------+---------------+--------------+----------------+                Figure 12: Generic TRIP Route Format   Address Family:   The address family field gives the type of address for the route.   Three address families are defined in this Section:            Code              Address Family            1                 Decimal Routing Numbers            2                 PentaDecimal Routing Numbers            3                 E.164 Numbers   This document reserves address family code 0.  This document reserves   address family codes 32768-65535 for vendor-specific applications   (these are the codes with the first bit of the code value equal to   1).  Additional address families may be defined in the future.   Assignment of address family codes is controlled by IANA.  SeeSection 13 for IANA considerations.Rosenberg, et. al.          Standards Track                    [Page 25]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   Application Protocol:   The application protocol gives the protocol for which this routing   table is maintained.  The currently defined application protocols   are:            Code              Protocol            1                 SIP            2                 H.323-H.225.0-Q.931            3                 H.323-H.225.0-RAS            4                 H.323-H.225.0-Annex-G   This document reserves application protocol code 0.  This document   reserves application protocol codes 32768-65535 for vendor-specific   applications (these are the codes with the first bit of the code   value equal to 1).  Additional application protocols may be defined   in the future.  Assignment of application protocol codes is   controlled by IANA.  SeeSection 13 for IANA considerations.   Length:   The length of the address field, in bytes.   Address:   This is an address (prefix) of the family type given by Address   Family.  The octet length of the address is variable and is   determined by the length field of the route.5.1.1.2. Decimal Routing Numbers   The Decimal Routing Numbers address family is a super set of all   E.164 numbers, national numbers, local numbers, and private numbers.   It can also be used to represent the decimal routing numbers used in   conjunction with Number Portability in some countries/regions.  A set   of telephone numbers is specified by a Decimal Routing Number prefix.   Decimal Routing Number prefixes are represented by a string of   digits, each digit encoded by its ASCII character representation.   This routing object covers all phone numbers starting with this   prefix.  The syntax for the Decimal Routing Number prefix is:      Decimal-routing-number  = *decimal-digit      decimal-digit           = DECIMAL-DIGIT      DECIMAL-DIGIT           = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"   This DECIMAL Routing Number prefix is not bound in length.  This   format is similar to the format for a global telephone number as   defined in SIP [8] without visual separators and without the "+"   prefix for international numbers.  This format facilitates efficient   comparison when using TRIP to route SIP or H323, both of which use   character based representations of phone numbers.  The prefix lengthRosenberg, et. al.          Standards Track                    [Page 26]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   is determined from the length field of the route.  The type of   Decimal Routing Number (private, local, national, or international)   can be deduced from the first few digits of the prefix.5.1.1.3. PentaDecimal Routing Numbers   This address family is used to represent PentaDecimal Routing Numbers   used in conjunction with Number Portability in some   countries/regions.  PentaDecimal Routing Number prefixes are   represented by a string of digits, each digit encoded by its ASCII   character representation.  This routing object covers all routing   numbers starting with this prefix.  The syntax for the PentaDecimal   Routing Number prefix is:      PentaDecimal-routing-number   = *pentadecimal-digit      pentadecimal-routing-digit    = PENTADECIMAL-DIGIT      PENTADECIMAL-DIGIT            = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|                                      "8"|"9"|"A"|"B"|"C"|"D"|"E"   Note the difference in alphabets between Decimal Routing Numbers and   PentaDecimal Routing Numbers.  A PentaDecimal Routing Number prefix   is not bound in length.   Note that the address family, which suits the routing numbers of a   specific country/region depends on the alphabets used for routing   numbers in that country/region.  For example, North American routing   numbers SHOULD use the Decimal Routing Numbers address family,   because their alphabet is limited to the digits "0" through "9".   Another example, in most European countries routing numbers use the   alphabet "0" through "9" and "A" through "E", and hence these   countries SHOULD use the PentaDecimal Routing Numbers address family.5.1.1.4. E.164 Numbers   The E.164 Numbers address family is dedicated to fully qualified   E.164 numbers.  A set of telephone numbers is specified by a E.164   prefix.  E.164 prefixes are represented by a string of digits, each   digit encoded by its ASCII character representation.  This routing   object covers all phone numbers starting with this prefix.  The   syntax for the E.164 prefix is:      E164-number          = *e164-digit      E164-digit           = E164-DIGIT      E164-DIGIT           = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"Rosenberg, et. al.          Standards Track                    [Page 27]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   This format facilitates efficient comparison when using TRIP to route   SIP or H323, both of which use character based representations of   phone numbers.  The prefix length is determined from the length field   of the route.   The E.164 Numbers address family and the Decimal Routing Numbers   address family have the same alphabet.  The E.164 Numbers address   family SHOULD be used whenever possible.  The Decimal Routing Numbers   address family can be used in case of private numbering plans or   applications that do not desire to advertise fully expanded, fully   qualified telephone numbers.  If Decimal Routing Numbers are used to   advertise non-fully qualified prefixes, the prefixes may have to be   manipulated (e.g. expanded) at the boundary between ITADs.  This adds   significant complexity to the ITAD-Border LS, because, it has to map   the prefixes from the format used in its own ITAD to the format used   in the peer ITAD.5.2. ReachableRoutes   Conditional Mandatory: False.   Required Flags: Well-known.   Potential Flags: Link-State Encapsulation (when flooding).   TRIP Type Code: 2   The ReachableRoutes attribute specifies a set of routes that are to   be added to service by the receiving LS(s).  The set of routes MAY be   empty, as indicated by setting the length field to zero.5.2.1. Syntax of ReachableRoutes   The ReachableRoutes Attribute has the same syntax as the   WithdrawnRoutes Attribute.  SeeSection 5.1.1.5.2.2. Route Origination and ReachableRoutes   Routes are injected into TRIP by a method outside the scope of this   specification.  Possible methods include a front-end protocol, an   intra-domain routing protocol, or static configuration.5.2.3. Route Selection and ReachableRoutes   The routes in ReachableRoutes are necessary for route selection.5.2.4. Aggregation and ReachableRoutes   To aggregate multiple routes, the set of ReachableRoutes to be   aggregated MUST combine to form a less specific set.Rosenberg, et. al.          Standards Track                    [Page 28]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   There is no mechanism within TRIP to communicate that a particular   address prefix is not used and thus that these addresses could be   skipped during aggregation.  LSs MAY use methods outside of TRIP to   learn of invalid prefixes that may be ignored during aggregation.   If an LS advertises an aggregated route, it MUST include the   AtomicAggregate attribute.5.2.5. Route Dissemination and ReachableRoutes   The ReachableRoutes attribute is recomputed at each LS except where   flooding is being used (e.g., within a domain).  It is therefore   possible for an LS to change the Application Protocol field of a   route before advertising that route to an external peer.   If an LS changes the Application Protocol of a route it advertises,   it MUST include the ConvertedRoute attribute in the UPDATE message.5.2.6. Aggregation Specifics for Decimal Routing Numbers, E.164 Numbers,       and PentaDecimal Routing Numbers   An LS that has routes to all valid numbers in a specific prefix   SHOULD advertise that prefix as the ReachableRoutes, even if there   are more specific prefixes that do not actually exist on the PSTN.   Generally, it takes 10 Decimal Routing/E.164 prefixes, or 15   PentaDecimal Routing prefixes, of length n to aggregate into a prefix   of length n-1.  However, if an LS is aware that a prefix is an   invalid Decimal Routing/E.164 prefix, or PentaDecimal Routing prefix,   then the LS MAY aggregate by skipping this prefix.  For example, if   the Decimal Routing prefix 19191 is known not to exist, then an LS   can aggregate to 1919 without 19191.  A prefix representing an   invalid set of PSTN destinations is sometimes referred to as a   "black-hole."  The method by which an LS is aware of black-holes is   not within the scope of TRIP, but if an LS has such knowledge, it can   use the knowledge when aggregating.5.3. NextHopServer   Conditional Mandatory: True (if ReachableRoutes and/or   WithdrawnRoutes attribute is present).   Required Flags: Well-known.   Potential Flags: None.   TRIP Type Code: 3.Rosenberg, et. al.          Standards Track                    [Page 29]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   Given a route with application protocol A and destinations D, the   NextHopServer indicates to the next-hop that messages of protocol A   destined for D should be sent to it.  This may or may not represent   the ultimate destination of those messages.5.3.1. NextHopServer Syntax   For generality, the address of the next-hop server may be of various   types (domain name, IPv4, IPv6, etc).  The NextHopServer attribute   includes the ITAD number of next-hop server, a length field, and a   next-hop name or address.   The syntax for the NextHopServer is given in Figure 13.    0                   1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +---------------+---------------+--------------+----------------+   |                         Next Hop ITAD                         |   +---------------+---------------+--------------+----------------+   |             Length            |         Server (variable)    ...   +---------------+---------------+--------------+----------------+                  Figure 13: NextHopServer Syntax   The Next-Hop ITAD indicates the domain of the next-hop.  Length field   gives the number of octets in the Server field, and the Server field   contains the name or address of the next-hop server.  The server   field is represented as a string of ASCII characters.  It is defined   as follows:   Server  = host [":" port ]   host    = <   A legal Internet host domain name              or an IPv4 address using the textual representation                 defined inSection 2.1 of RFC 1123 [9]              or an IPv6 address using the textual representation                 defined inSection 2.2 of RFC 2373 [10].  The IPv6                 address MUST be enclosed in "[" and "]"                 characters.>   port    = *DIGIT   If the port is empty or not given, the default port is assumed (e.g.,   port 5060 if the application protocol is SIP).5.3.2. Route Origination and NextHopServer   When an LS originates a routing object into TRIP, it MUST include a   NextHopServer within its domain.  The NextHopServer could be an   address of the egress gateway or of a signaling proxy.Rosenberg, et. al.          Standards Track                    [Page 30]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.3.3. Route Selection and NextHopServer   LS policy may prefer certain next-hops or next-hop domains over   others.5.3.4. Aggregation and NextHopServer   When aggregating multiple routing objects into a single routing   object, an LS MUST insert a new signaling server from within its   domain as the new NextHopServer unless all of the routes being   aggregated have the same next-hop.5.3.5. Route Dissemination and NextHopServer   When propagating routing objects to peers, an LS may choose to insert   a signaling proxy within its domain as the new next-hop, or it may   leave the next-hop unchanged.  Inserting a new next-hop will cause   the signaling messages to be sent to that address, and will provide   finer control over the signaling path.  Leaving the next-hop   unchanged will yield a more efficient signaling path (fewer hops).   It is a local policy decision of the LS to decide whether to   propagate or change the NextHopServer.5.4. AdvertisementPath   Conditional Mandatory: True (if ReachableRoutes and/or   WithdrawnRoutes attribute is present).   Required Flags: Well-known.   Potential Flags: None.   TRIP Type Code: 4.   This attribute identifies the ITADs through which routing information   carried in an advertisement has passed.  The AdvertisementPath   attribute is analogous to the AS_PATH attribute in BGP.  The   attributes differ in that BGP's AS_PATH also reflects the path to the   destination.  In TRIP, not every domain need modify the next-hop, so   the AdvertisementPath may include many more hops than the actual path   to the destination.  The RoutedPath attribute (Section 5.5) reflects   the actual signaling path to the destination.5.4.1. AdvertisementPath Syntax   AdvertisementPath is a variable length attribute that is composed of   a sequence of ITAD path segments.  Each ITAD path segment is   represented by a type-length-value triple.   The path segment type is a 1-octet long field with the following   values defined:Rosenberg, et. al.          Standards Track                    [Page 31]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002      Value      Segment Type      1          AP_SET: unordered set of ITADs a route in the                 advertisement message has traversed      2          AP_SEQUENCE: ordered set of ITADs a route in                 the advertisement message has traversed   The path segment length is a 1-octet long field containing the number   of ITADs in the path segment value field.   The path segment value field contains one or more ITAD numbers, each   encoded as a 4-octets long field.  ITAD numbers uniquely identify an   Internet Telephony Administrative Domain, and must be obtained from   IANA.  SeeSection 13 for procedures to obtain an ITAD number from   IANA.5.4.2. Route Origination and AdvertisementPath   When an LS originates a route then:      -  The originating LS shall include its own ITAD number in the         AdvertisementPath attribute of all advertisements sent to LSs         located in neighboring ITADs.  In this case, the ITAD number of         the originating LS's ITAD will be the only entry in the         AdvertisementPath attribute.      -  The originating LS shall include an empty AdvertisementPath         attribute in all advertisements sent to LSs located in its own         ITAD.  An empty AdvertisementPath attribute is one whose length         field contains the value zero.5.4.3. Route Selection and AdvertisementPath   The AdvertisementPath may be used for route selection.  Possible   criteria to be used are the number of hops on the path and the   presence or absence of particular ITADs on the path.   As discussed inSection 10, the AdvertisementPath is used to prevent   routing information from looping.  If an LS receives a route with its   own ITAD already in the AdvertisementPath, the route MUST be   discarded.5.4.4. Aggregation and AdvertisementPath   The rules for aggregating AdvertisementPath attributes are given in   the following sections, where the term "path" used inSection 5.4.4.1   and 5.4.4.2 is understood to mean AdvertisementPath.Rosenberg, et. al.          Standards Track                    [Page 32]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.4.4.1. Aggregating Routes with Identical Paths   If all routes to be aggregated have identical path attributes, then   the aggregated route has the same path attribute as the individual   routes.5.4.4.2. Aggregating Routes with Different Paths   For the purpose of aggregating path attributes we model each ITAD   within the path as a pair <type, value>, where "type" identifies a   type of the path segment (AP_SEQUENCE or AP_SET), and "value" is the   ITAD number.  Two ITADs are said to be the same if their   corresponding <type, value> are the same.   If the routes to be aggregated have different path attributes, then   the aggregated path attribute shall satisfy all of the following   conditions:      -  All pairs of the type AP_SEQUENCE in the aggregated path MUST         appear in all of the paths of routes to be aggregated.      -  All pairs of the type AP_SET in the aggregated path MUST appear         in at least one of the paths of the initial set (they may         appear as either AP_SET or AP_SEQUENCE types).      -  For any pair X of the type AP_SEQUENCE that precedes pair Y in         the aggregated path, X precedes Y in each path of the initial         set that contains Y, regardless of the type of Y.      -  No pair with the same value shall appear more than once in the         aggregated path, regardless of the pair's type.   An implementation may choose any algorithm that conforms to these   rules.  At a minimum, a conformant implementation MUST be able to   perform the following algorithm that meets all of the above   conditions:      -  Determine the longest leading sequence of tuples (as defined         above) common to all the paths of the routes to be aggregated.         Make this sequence the leading sequence of the aggregated path.      -  Set the type of the rest of the tuples from the paths of the         routes to be aggregated to AP_SET, and append them to the         aggregated path.      -  If the aggregated path has more than one tuple with the same         value (regardless of tuple's type), eliminate all but one such         tuple by deleting tuples of the type AP_SET from the aggregated         path.   An implementation that chooses to provide a path aggregation   algorithm that retains significant amounts of path information may   wish to use the procedure ofSection 5.4.4.3.Rosenberg, et. al.          Standards Track                    [Page 33]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.4.4.3. Example Path Aggregation Algorithm   An example algorithm to aggregate two paths works as follows:      -  Identify the ITADs (as defined inSection 5.4.1) within each         path attribute that are in the same relative order within both         path attributes.  Two ITADs, X and Y, are said to be in the         same order if either X precedes Y in both paths, or if Y         precedes X in both paths.      -  The aggregated path consists of ITADs identified in (a) in         exactly the same order as they appear in the paths to be         aggregated.  If two consecutive ITADs identified in (a) do not         immediately follow each other in both of the paths to be         aggregated, then the intervening ITADs (ITADs that are between         the two consecutive ITADs that are the same) in both attributes         are combined into an AP_SET path segment that consists of the         intervening ITADs from both paths; this segment is then placed         in between the two consecutive ITADs identified in (a) of the         aggregated attribute.  If two consecutive ITADs identified in         (a) immediately follow each other in one attribute, but do not         follow in another, then the intervening ITADs of the latter are         combined into an AP_SET path segment; this segment is then         placed in between the two consecutive ITADs identified in (a)         of the aggregated path.   If as a result of the above procedure a given ITAD number appears   more than once within the aggregated path, all but the last instance   (rightmost occurrence) of that ITAD number should be removed from the   aggregated path.5.4.5. Route Dissemination and AdvertisementPath   When an LS propagates a route which it has learned from another LS,   it shall modify the route's AdvertisementPath attribute based on the   location of the LS to which the route will be sent.      -  When a LS advertises a route to another LS located in its own         ITAD, the advertising LS MUST NOT modify the AdvertisementPath         attribute associated with the route.      -  When a LS advertises a route to an LS located in a neighboring         ITAD, then the advertising LS MUST update the AdvertisementPath         attribute as follows:Rosenberg, et. al.          Standards Track                    [Page 34]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002         *  If the first path segment of the AdvertisementPath is of            type AP_SEQUENCE, the local system shall prepend its own            ITAD number as the last element of the sequence (put it in            the leftmost position).         *  If the first path segment of the AdvertisementPath is of            type AP_SET, the local system shall prepend a new path            segment of type AP_SEQUENCE to the AdvertisementPath,            including its own ITAD number in that segment.5.5. RoutedPath   Conditional Mandatory: True   (if ReachableRoutes attribute is present).   Required Flags: Well-known.   Potential Flags: None.   TRIP Type Code: 5.   This attribute identifies the ITADs through which messages sent using   this route would pass.  The ITADs in this path are a subset of those   in the AdvertisementPath.5.5.1. RoutedPath Syntax   The syntax of the RoutedPath attribute is the same as that of the   AdvertisementPath attribute.  SeeSection 5.4.1.5.5.2. Route Origination and RoutedPath   When an LS originates a route it MUST include the RoutedPath   attribute.      -  The originating LS shall include its own ITAD number in the         RoutedPath attribute of all advertisements sent to LSs located         in neighboring ITADs.  In this case, the ITAD number of the         originating LS's ITAD will be the only entry in the RoutedPath         attribute.      -  The originating LS shall include an empty RoutedPath attribute         in all advertisements sent to LSs located in its own ITAD.  An         empty RoutedPath attribute is one whose length field contains         the value zero.5.5.3. Route Selection and RoutedPath   The RoutedPath MAY be used for route selection, and in most cases is   preferred over the AdvertisementPath for this role.  Some possible   criteria to be used are the number of hops on the path and the   presence or absence of particular ITADs on the path.Rosenberg, et. al.          Standards Track                    [Page 35]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.5.4. Aggregation and RoutedPath   The rules for aggregating RoutedPath attributes are given inSection5.4.4.1 and 5.4.4.2, where the term "path" used inSection 5.4.4.1   and 5.4.4.2 is understood to mean RoutedPath.5.5.5. Route Dissemination and RoutedPath   When an LS propagates a route that it learned from another LS, it   modifies the route's RoutedPath attribute based on the location of   the LS to which the route is sent.      -  When an LS advertises a route to another LS located in its own         ITAD, the advertising LS MUST NOT modify the RoutedPath         attribute associated with the route.      -  If the LS has not changed the NextHopServer attribute, then the         LS MUST NOT change the RoutedPath attribute.      -  Otherwise, the LS changed the NextHopServer and is advertising         the route to an LS in another ITAD.  The advertising LS MUST         update the RoutedPath attribute as follows:         *  If the first path segment of the RoutedPath is of type            AP_SEQUENCE, the local system shall prepend its own ITAD            number as the last element of the sequence (put it in the            leftmost position).         *  If the first path segment of the RoutedPath is of type            AP_SET, the local system shall prepend a new path segment of            type AP_SEQUENCE to the RoutedPath, including its own ITAD            number in that segment.5.6. AtomicAggregate   Conditional Mandatory: False.   Required Flags: Well-known.   Potential Flags: None.   TRIP Type Code: 6.   The AtomicAggregate attribute indicates that a route may traverse   domains not listed in the RoutedPath.  If an LS, when presented with   a set of overlapping routes from a peer LS, selects the less specific   route without selecting the more specific route, then the LS includes   the AtomicAggregate attribute with the routing object.5.6.1. AtomicAggregate Syntax   This attribute has length zero (0); the value field is empty.Rosenberg, et. al.          Standards Track                    [Page 36]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.6.2. Route Origination and AtomicAggregate   Routes are never originated with the AtomicAggregate attribute.5.6.3. Route Selection and AtomicAggregate   The AtomicAggregate attribute may be used in route selection - it   indicates that the RoutedPath may be incomplete.5.6.4. Aggregation and AtomicAggregate   If any of the routes to aggregate has the AtomicAggregate attribute,   then so MUST the resultant aggregate.5.6.5. Route Dissemination and AtomicAggregate   If an LS, when presented with a set of overlapping routes from a peer   LS, selects the less specific route (seeSection 0) without selecting   the more specific route, then the LS MUST include the AtomicAggregate   attribute with the routing object (if it is not already present).   An LS receiving a routing object with an AtomicAggregate attribute   MUST NOT make the set of destinations more specific when advertising   it to other LSs, and MUST NOT remove the attribute when propagating   this object to a peer LS.5.7. LocalPreference   Conditional Mandatory: False.   Required Flags: Well-known.   Potential Flags: None.   TRIP Type Code: 7.   The LocalPreference attribute is only used intra-domain, it indicates   the local LS's preference for the routing object to other LSs within   the same domain.  This attribute MUST NOT be included when   communicating to an LS in another domain, and MUST be included over   intra-domain links.5.7.1. LocalPreference Syntax   The LocalPreference attribute is a 4-octet unsigned numeric value.  A   higher value indicates a higher preference.Rosenberg, et. al.          Standards Track                    [Page 37]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.7.2. Route Origination and LocalPreference   Routes MUST NOT be originated with the LocalPreference attribute to   inter-domain peers.  Routes to intra-domain peers MUST be originated   with the LocalPreference attribute.5.7.3. Route Selection and LocalPreference   The LocalPreference attribute allows one LS in a domain to calculate   a preference for a route, and to communicate this preference to other   LSs within the domain.5.7.4. Aggregation and LocalPreference   The LocalPreference attribute is not affected by aggregation.5.7.5. Route Dissemination and LocalPreference   An LS MUST include the LocalPreference attribute when communicating   with peer LSs within its own domain.  An LS MUST NOT include the   LocalPreference attribute when communicating with LSs in other   domains.  LocalPreference attributes received from inter-domain peers   MUST be ignored.5.8. MultiExitDisc   Conditional Mandatory: False.   Required Flags: Well-known.   Potential Flags: None.   TRIP Type Code: 8.   When two ITADs are connected by more than one set of peers, the   MultiExitDisc attribute may be used to specify preferences for routes   received over one of those links versus routes received over other   links.  The MultiExitDisc parameter is used only for route selection.5.8.1. MultiExitDisc Syntax   The MultiExitDisc attribute carries a 4-octet unsigned numeric value.   A higher value represents a more preferred routing object.5.8.2. Route Origination and MultiExitDisc   Routes originated to intra-domain peers MUST NOT be originated with   the MultiExitDisc attribute.  When originating a route to an inter-   domain peer, the MultiExitDisc attribute may be included.Rosenberg, et. al.          Standards Track                    [Page 38]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.8.3. Route Selection and MultiExitDisc   The MultiExitDisc attribute is used to express a preference when   there are multiple links between two domains.  If all other factors   are equal, then a route with a higher MultiExitDisc attribute is   preferred over a route with a lower MultiExitDisc attribute.5.8.4. Aggregation and MultiExitDisc   Routes with differing MultiExitDisc parameters MUST NOT be   aggregated.  Routes with the same value in the MultiExitDisc   attribute MAY be aggregated and the same MultiExitDisc attribute   attached to the aggregated object.5.8.5. Route Dissemination and MultiExitDisc   If received from a peer LS in another domain, an LS MAY propagate the   MultiExitDisc to other LSs within its domain.  The MultiExitDisc   attribute MUST NOT be propagated to LSs in other domains.   An LS may add the MultiExitDisc attribute when propagating routing   objects to an LS in another domain.  The inclusion of the   MultiExitDisc attribute is a matter of policy, as is the value of the   attribute.5.9. Communities   Conditional Mandatory: False.   Required Flags: Not Well-Known, Independent Transitive.   Potential Flags: None.   TRIP Type Code: 9.   A community is a group of destinations that share some common   property.   The Communities attribute is used to group destinations so that the   routing decision can be based on the identity of the group.  Using   the Communities attribute should significantly simplify the   distribution of routing information by providing an administratively   defined aggregation unit.   Each ITAD administrator may define the communities to which a   particular route belongs.  By default, all routes belong to the   general Internet Telephony community.   As an example, the Communities attribute could be used to define an   alliance between a group of Internet Telephony service providers for   a specific subset of routing information.  In this case, members ofRosenberg, et. al.          Standards Track                    [Page 39]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   that alliance would accept only routes for destinations in this group   that are advertised by other members of the alliance.  Other   destinations would be more freely accepted.  To achieve this, a   member would tag each route with a designated Community attribute   value before disseminating it.  This relieves the members of such an   alliance, from the responsibility of keeping track of the identities   of all other members of that alliance.   Another example use of the Communities attribute is with aggregation.   It is often useful to advertise both the aggregate route and the   component more-specific routes that were used to form the aggregate.   These information components are only useful to the neighboring TRIP   peer, and perhaps the ITAD of the neighboring TRIP peer, so it is   desirable to filter out the component routes.  This can be achieved   by specifying a Community attribute value that the neighboring peers   will match and filter on.  That way it can be assured that the more   specific routes will not propagate beyond their desired scope.5.9.1. Syntax of Communities   The Communities attribute is of variable length.  It consists of a   set of 8-octet values, each of which specifies a community.  The   first 4 octets of the Community value are the Community ITAD Number   and the next 4 octets are the Community ID.   0                   1                   2                   3   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +---------------+---------------+--------------+----------------+   |                       Community ITAD Number 1                 |   +---------------+---------------+--------------+----------------+   |                         Community ID 1                        |   +---------------+---------------+--------------+----------------+   |                       . . . . . . . . .   +---------------+---------------+--------------+----------------+                    Figure 14: Communities Syntax   For administrative assignment, the following assumptions may be made:      The Community attribute values starting with a Community ITAD      Number of 0x00000000 are hereby reserved.   The following communities have global significance and their   operation MUST be implemented in any Community attribute-aware TRIP   LS.Rosenberg, et. al.          Standards Track                    [Page 40]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002      -  NO_EXPORT (Community ITAD Number = 0x00000000 and Community ID         = 0xFFFFFF01).  Any received route with a community attribute         containing this value MUST NOT be advertised outside of the         receiving TRIP ITAD.   Other community values MUST be encoded using an ITAD number in the   four most significant octets.  The semantics of the final four octets   (the Community ID octets) may be defined by the ITAD (e.g., ITAD 690   may define research, educational, and commercial community IDs that   may be used for policy routing as defined by the operators of that   ITAD).5.9.2. Route Origination and Communities   The Communities attribute is not well-known.  If a route has a   Communities attribute associated with it, the LS MUST include that   attribute in the advertisement it originates.5.9.3. Route Selection and Communities   The Communities attribute may be used for route selection.  A route   that is a member of a certain community may be preferred over another   route that is not a member of that community.  Likewise, routes   without a certain community value may be excluded from consideration.5.9.4. Aggregation and Communities   If a set of routes is to be aggregated and the resultant aggregate   does not carry an Atomic_Aggregate attribute, then the resulting   aggregate should have a Communities attribute that contains the union   of the Community attributes of the aggregated routes.5.9.5. Route Dissemination and Communities   An LS may manipulate the Communities attribute before disseminating a   route to a peer.  Community attribute manipulation may include adding   communities, removing communities, adding a Communities attribute (if   none exists), deleting the Communities attribute, etc.5.10. ITAD Topology   Conditional Mandatory: False.   Required Flags: Well-known, Link-State encapsulated.   Potential Flags: None.   TRIP Type Code: 10.Rosenberg, et. al.          Standards Track                    [Page 41]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   Within an ITAD, each LS must know the status of other LSs so that LS   failure can be detected.  To do this, each LS advertises its internal   topology to other LSs within the domain.  When an LS detects that   another LS is no longer active, the information sourced by that LS   can be deleted (the Adj-TRIB-In for that peer may be cleared).  The   ITAD Topology attribute is used to communicate this information to   other LSs within the domain.   An LS MUST send a topology update each time it detects a change in   its internal peer set.  The topology update may be sent in an UPDATE   message by itself or it may be piggybacked on an UPDATE message which   includes ReachableRoutes and/or WithdrawnRoutes information.   When an LS receives a topology update from an internal LS, it MUST   recalculate which LSs are active within the ITAD via a connectivity   algorithm on the topology.5.10.1. ITAD Topology Syntax   The ITAD Topology attribute indicates the LSs with which the LS is   currently peering.  The attribute consists of a list of the TRIP   Identifiers with which the LS is currently peering, the format is   given in  Figure 15.  This attribute MUST use the link-state   encapsulation as defined inSection 4.3.2.4.    0                   1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +---------------+---------------+--------------+----------------+   |                        TRIP Identifier 1                      |   +---------------+---------------+--------------+----------------+   |                        TRIP Identifier 2 ...                  |   +---------------+---------------+--------------+----------------+                   Figure 15: ITAD Topology Syntax5.10.2. Route Origination and ITAD Topology   The ITAD Topology attribute is independent of any routes in the   UPDATE.  Whenever the set of internal peers of an LS changes, it MUST   create an UPDATE with the ITAD Topology Attribute included listing   the current set of internal peers.  The LS MUST include this   attribute in the first UPDATE it sends to a peer after the peering   session is established.Rosenberg, et. al.          Standards Track                    [Page 42]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.10.3. Route Selection and ITAD Topology   This attribute is independent of any routing information in the   UPDATE.  When an LS receives an UPDATE with an ITAD Topology   attribute, it MUST compute the set of LSs currently active in the   domain by performing a connectivity test on the ITAD topology as   given by the set of originated ITAD Topology attributes.  The LS MUST   locally purge the Adj-TRIB-In for any LS that is no longer active in   the domain.  The LS MUST NOT propagate this purging information to   other LSs as they will make a similar decision.5.10.4. Aggregation and ITAD Topology   This information is not aggregated.5.10.5. Route Dissemination and ITAD Topology   An LS MUST ignore the attribute if received from a peer in another   domain.  An LS MUST NOT send this attribute to an inter-domain peer.5.11. ConvertedRoute   Conditional Mandatory: False.   Required Flags: Well-known.   Potential Flags: None.   TRIP Type Code: 12.   The ConvertedRoute attribute indicates that an intermediate LS has   altered the route by changing the route's Application Protocol.  For   example, if an LS receives a route with Application Protocol X and   changes the Application Protocol to Y before advertising the route to   an external peer, the LS MUST include the ConvertedRoute attribute.   The attribute is an indication that the advertised application   protocol will not be used end-to-end, i.e., the information   advertised about this route is not complete.5.11.1. ConvertedRoute Syntax   This attribute has length zero (0); the value field is empty.5.11.2. Route Origination and ConvertedRoute   Routes are never originated with the ConvertedRoute attribute.Rosenberg, et. al.          Standards Track                    [Page 43]

RFC 3219            Telephony Routing over IP (TRIP)        January 20025.11.3. Route Selection and ConvertedRoute   The ConvertedRoute attribute may be used in route selection - it   indicates that advertised routing information is not complete.5.11.4. Aggregation and ConvertedRoute   If any of the routes to aggregate has the ConvertedRoute attribute,   then so MUST the resultant aggregate.5.11.5. Route Dissemination and ConvertedRoute   If an LS changes the Application Protocol of a route before   advertising the route to an external peer, the LS MUST include the   ConvertedRoute attribute.5.12. Considerations for Defining New TRIP Attributes   Any proposal for defining new TRIP attributes should specify the   following:      -  the use of this attribute,      -  the attribute's flags,      -  the attribute's syntax,      -  how the attribute works with route origination,      -  how the attribute works with route aggregation, and      -  how the attribute works with route dissemination and the         attribute's scope (e.g., intra-domain only like         LocalPreference)   IANA will manage the assignment of TRIP attribute type codes to new   attributes.6. TRIP Error Detection and Handling   This section describes errors to be detected and the actions to be   taken while processing TRIP messages.   When any of the conditions described here are detected, a   NOTIFICATION message with the indicated Error Code, Error Subcode,   and Data fields MUST be sent, and the TRIP connection MUST be closed.   If no Error Subcode is specified, then a zero Subcode MUST be used.   The phrase "the TRIP connection is closed" means that the transport   protocol connection has been closed and that all resources for that   TRIP connection have been de-allocated.  If the connection was   inter-domain, then routing table entries associated with the remote   peer MUST be marked as invalid.  Routing table entries MUST NOT beRosenberg, et. al.          Standards Track                    [Page 44]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   marked as invalid if an internal peering session is terminated.  The   fact that the routes have been marked as invalid is passed to other   TRIP peers before the routes are deleted from the system.   Unless specified explicitly, the Data field of the NOTIFICATION   message that is sent to indicate an error MUST be empty.6.1. Message Header Error Detection and Handling   All errors detected while processing the Message Header are indicated   by sending the NOTIFICATION message with the Error Code Message   Header Error.  The Error Subcode elaborates on the specific nature of   the error.  The error checks in this section MUST be performed by   each LS upon receipt of every message.   If the Length field of the message header is less than 3 or greater   than 4096, or if the Length field of an OPEN message is less than the   minimum length of the OPEN message, or if the Length field of an   UPDATE message is less than the minimum length of the UPDATE message,   or if the Length field of a KEEPALIVE message is not equal to 3, or   if the Length field of a NOTIFICATION message is less than the   minimum length of the NOTIFICATION message, then the Error Subcode   MUST be set to Bad Message Length.  The Data field contains the   erroneous Length field.   If the Type field of the message header is not recognized, then the   Error Subcode MUST be set to "Bad Message Type."  The Data field   contains the erroneous Type field.6.2. OPEN Message Error Detection and Handling   All errors detected while processing the OPEN message are indicated   by sending the NOTIFICATION message with the Error Code "OPEN Message   Error."  The Error Subcode elaborates on the specific nature of the   error.  The error checks in this section MUST be performed by each LS   upon receipt of every OPEN message.   If the version number contained in the Version field of the received   OPEN message is not supported, then the Error Subcode MUST be set to   "Unsupported Version Number."  The Data field is a 1-octet unsigned   integer, which indicates the largest locally supported version   number, which is less than the version of the remote TRIP peer bid   (as indicated in the received OPEN message).   If the ITAD field of the OPEN message is unacceptable, then the Error   Subcode MUST be set to "Bad Peer ITAD."  The determination of   acceptable ITAD numbers is outside the scope of this protocol.Rosenberg, et. al.          Standards Track                    [Page 45]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   If the Hold Time field of the OPEN message is unacceptable, then the   Error Subcode MUST be set to "Unacceptable Hold Time."  An   implementation MUST reject Hold Time values of one or two seconds.   An implementation MAY reject any proposed Hold Time.  An   implementation that accepts a Hold Time MUST use the negotiated value   for the Hold Time.   If the TRIP Identifier field of the OPEN message is not valid, then   the Error Subcode MUST be set to "Bad TRIP Identifier."  A TRIP   identifier is 4-octets in length and can take any value.  An LS   considers the TRIP Identifier invalid if it already has an open   connection with another peer LS that has the same ITAD and TRIP   Identifier.   Any two LSs within the same ITAD MUST NOT have equal TRIP Identifier   values.  This restriction does not apply to LSs in different ITADs   since the purpose is to uniquely identify an LS using its TRIP   Identifier and its ITAD number.   If one of the Optional Parameters in the OPEN message is not   recognized, then the Error Subcode MUST be set to "Unsupported   Optional Parameters."   If the Optional Parameters of the OPEN message include Capability   Information with an unsupported capability (unsupported in either   capability type or value), then the Error Subcode MUST be set to   "Unsupported Capability," and the entirety of the unsupported   capabilities MUST be listed in the Data field of the NOTIFICATION   message.   If the Optional Parameters of the OPEN message include Capability   Information which does not match the receiving LS's capabilities,   then the Error Subcode MUST be set to "Capability Mismatch," and the   entirety of the mismatched capabilities MUST be listed in the Data   field of the NOTIFICATION message.6.3. UPDATE Message Error Detection and Handling   All errors detected while processing the UPDATE message are indicated   by sending the NOTIFICATION message with the Error Code "UPDATE   Message Error."  The Error Subcode elaborates on the specific nature   of the error.  The error checks in this section MUST be performed by   each LS upon receipt of every UPDATE message.  These error checks   MUST occur before flooding procedures are invoked with internal   peers.Rosenberg, et. al.          Standards Track                    [Page 46]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   If any recognized attribute has Attribute Flags that conflict with   the Attribute Type Code, then the Error Subcode MUST be set to   "Attribute Flags Error."  The Data field contains the erroneous   attribute (type, length and value).   If any recognized attribute has an Attribute Length that conflicts   with the expected length (based on the attribute type code), then the   Error Subcode MUST be set to "Attribute Length Error."  The Data   field contains the erroneous attribute (type, length and value).   If any of the mandatory (i.e., conditional mandatory attribute and   the conditions for including it in the UPDATE message are fulfilled)   well-known attributes are not present, then the Error Subcode MUST be   set to "Missing Well-known Mandatory Attribute."  The Data field   contains the Attribute Type Code of the missing well-known   conditional mandatory attributes.   If any of the well-known attributes are not recognized, then the   Error Subcode MUST be set to "Unrecognized Well-known Attribute."   The Data field contains the unrecognized attribute (type, length and   value).   If any attribute has a syntactically incorrect value, or an undefined   value, then the Error Subcode is set to "Invalid Attribute."  The   Data field contains the incorrect attribute (type, length and value).   Such a NOTIFICATION message is sent, for example, when a   NextHopServer attribute is received with an invalid address.   The information carried by the AdvertisementPath attribute is checked   for ITAD loops.  ITAD loop detection is done by scanning the full   AdvertisementPath, and checking that the ITAD number of the local   ITAD does not appear in the AdvertisementPath.  If the local ITAD   number appears in the AdvertisementPath, then the route MAY be stored   in the Adj-TRIB-In.  However unless the LS is configured to accept   routes with its own ITAD in the advertisement path, the route MUST   not be passed to the TRIP Decision Process.  The operation of an LS   that is configured to accept routes with its own ITAD number in the   advertisement path are outside the scope of this document.   If the UPDATE message was received from an internal peer and either   the WithdrawnRoutes, ReachableRoutes, or ITAD Topology attribute does   not have the Link-State Encapsulation flag set, then the Error   Subcode is set to "Invalid Attribute" and the data field contains the   attribute.  Likewise, the attribute is invalid if received from an   external peer and the Link-State Flag is set.   If any attribute appears more than once in the UPDATE message, then   the Error Subcode is set to "Malformed Attribute List."Rosenberg, et. al.          Standards Track                    [Page 47]

RFC 3219            Telephony Routing over IP (TRIP)        January 20026.4. NOTIFICATION Message Error Detection and Handling   If a peer sends a NOTIFICATION message, and there is an error in that   message, there is unfortunately no means of reporting this error via   a subsequent NOTIFICATION message.  Any such error, such as an   unrecognized Error Code or Error Subcode, should be noticed, logged   locally, and brought to the attention of the administration of the   peer.  The means to do this, however, are outside the scope of this   document.6.5. Hold Timer Expired Error Handling   If a system does not receive successive messages within the period   specified by the negotiated Hold Time, then a NOTIFICATION message   with a "Hold Timer Expired" Error Code MUST be sent and the TRIP   connection MUST be closed.6.6. Finite State Machine Error Handling   An error detected by the TRIP Finite State Machine (e.g., receipt of   an unexpected event) MUST result in sending a NOTIFICATION message   with the Error Code "Finite State Machine Error" and the TRIP   connection MUST be closed.6.7. Cease   In the absence of any fatal errors (that are indicated in this   section), a TRIP peer MAY choose at any given time to close its TRIP   connection by sending the NOTIFICATION message with the Error Code   "Cease."  However, the Cease NOTIFICATION message MUST NOT be used   when a fatal error indicated by this section exists.6.8. Connection Collision Detection   If a pair of LSs try simultaneously to establish a transport   connection to each other, then two parallel connections between this   pair of speakers might well be formed.  We refer to this situation as   connection collision.  Clearly, one of these connections must be   closed.   Based on the value of the TRIP Identifier, a convention is   established for detecting which TRIP connection is to be preserved   when a collision occurs.  The convention is to compare the TRIP   Identifiers of the peers involved in the collision and to retain only   the connection initiated by the LS with the higher-valued TRIP   Identifier.Rosenberg, et. al.          Standards Track                    [Page 48]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   Upon receipt of an OPEN message, the local LS MUST examine all of its   connections that are in the OpenConfirm state.  An LS MAY also   examine connections in an OpenSent state if it knows the TRIP   Identifier of the peer by means outside of the protocol.  If among   these connections there is a connection to a remote LS, whose TRIP   Identifier equals the one in the OPEN message, then the local LS MUST   perform the following collision resolution procedure:   The TRIP Identifier and ITAD of the local LS is compared to the TRIP   Identifier and ITAD of the remote LS (as specified in the OPEN   message).  TRIP Identifiers are treated as 4-octet unsigned integers   for comparison.   If the value of the local TRIP Identifier is less than the remote   one, or if the two TRIP Identifiers are equal and the value of the   ITAD of the local LS is less than value of the ITAD of the remote LS,   then the local LS MUST close the TRIP connection that already exists   (the one that is already in the OpenConfirm state), and accept the   TRIP connection initiated by the remote LS:      1. Otherwise, the local LS closes the newly created TRIP         connection and continues to use the existing one (the one that         is already in the OpenConfirm state).      2. If a connection collision occurs with an existing TRIP         connection that is in the Established state, then the LS MUST         unconditionally close off the newly created connection.  Note         that a connection collision cannot be detected with connections         in Idle, Connect, or Active states.      3. To close the TRIP connection (that results from the collision         resolution procedure), an LS MUST send a NOTIFICATION message         with the Error Code "Cease" and the TRIP connection MUST be         closed.7. TRIP Version Negotiation   Peer LSs may negotiate the version of the protocol by making multiple   attempts to open a TRIP connection, starting with the highest version   number each supports.  If an open attempt fails with an Error Code   "OPEN Message Error" and an Error Subcode "Unsupported Version   Number," then the LS has available the version number it tried, the   version number its peer tried, the version number passed by its peer   in the NOTIFICATION message, and the version numbers that it   supports.  If the two peers support one or more common versions, then   this will allow them to rapidly determine the highest common version.   In order to support TRIP version negotiation, future versions of TRIP   must retain the format of the OPEN and NOTIFICATION messages.Rosenberg, et. al.          Standards Track                    [Page 49]

RFC 3219            Telephony Routing over IP (TRIP)        January 20028. TRIP Capability Negotiation   An LS MAY include the Capabilities Option in its OPEN message to a   peer to indicate the capabilities supported by the LS.  An LS   receiving an OPEN message MUST NOT use any capabilities that were not   included in the OPEN message of the peer when communicating with that   peer.9. TRIP Finite State Machine   This section specifies TRIP operation in terms of a Finite State   Machine (FSM).  Following is a brief summary and overview of TRIP   operations by state as determined by this FSM.  A condensed version   of the TRIP FSM is found in Appendix 1.  There is one TRIP FSM per   peer and these FSMs operate independently.   Idle state:   Initially TRIP is in the Idle state for each peer.  In this state,   TRIP refuses all incoming connections.  No resources are allocated to   the peer.  In response to the Start event (initiated by either the   system or the operator), the local system initializes all TRIP   resources, starts the ConnectRetry timer, initiates a transport   connection to the peer, starts listening for a connection that may be   initiated by the remote TRIP peer, and changes its state to Connect.   The exact value of the ConnectRetry timer is a local matter, but   should be sufficiently large to allow TCP initialization.   If an LS detects an error, it closes the transport connection and   changes its state to Idle.  Transitioning from the Idle state   requires generation of the Start event.  If such an event is   generated automatically, then persistent TRIP errors may result in   persistent flapping of the LS.  To avoid such a condition, Start   events MUST NOT be generated immediately for a peer that was   previously transitioned to Idle due to an error.  For a peer that was   previously transitioned to Idle due to an error, the time between   consecutive Start events, if such events are generated automatically,   MUST exponentially increase.  The value of the initial timer SHOULD   be 60 seconds, and the time SHOULD be at least doubled for each   consecutive retry up to some maximum value.   Any other event received in the Idle state is ignored.   Connect State:   In this state, an LS is waiting for a transport protocol connection   to be completed to the peer, and is listening for inbound transport   connections from the peer.Rosenberg, et. al.          Standards Track                    [Page 50]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   If the transport protocol connection succeeds, the local LS clears   the ConnectRetry timer, completes initialization, sends an OPEN   message to its peer, sets its Hold Timer to a large value, and   changes its state to OpenSent.  A Hold Timer value of 4 minutes is   suggested.   If the transport protocol connect fails (e.g., retransmission   timeout), the local system restarts the ConnectRetry timer, continues   to listen for a connection that may be initiated by the remote LS,   and changes its state to Active state.   In response to the ConnectRetry timer expired event, the local LS   cancels any outstanding transport connection to the peer, restarts   the ConnectRetry timer, initiates a transport connection to the   remote LS, continues to listen for a connection that may be initiated   by the remote LS, and stays in the Connect state.   If the local LS detects that a remote peer is trying to establish a   connection to it and the IP address of the peer is not an expected   one, then the local LS rejects the attempted connection and continues   to listen for a connection from its expected peers without changing   state.   If an inbound transport protocol connection succeeds, the local LS   clears the ConnectRetry timer, completes initialization, sends an   OPEN message to its peer, sets its Hold Timer to a large value, and   changes its state to OpenSent.  A Hold Timer value of 4 minutes is   suggested.   The Start event is ignored in the Connect state.   In response to any other event (initiated by either the system or the   operator), the local system releases all TRIP resources associated   with this connection and changes its state to Idle.   Active state:   In this state, an LS is listening for an inbound connection from the   peer, but is not in the process of initiating a connection to the   peer.   If an inbound transport protocol connection succeeds, the local LS   clears the ConnectRetry timer, completes initialization, sends an   OPEN message to its peer, sets its Hold Timer to a large value, and   changes its state to OpenSent.  A Hold Timer value of 4 minutes is   suggested.Rosenberg, et. al.          Standards Track                    [Page 51]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   In response to the ConnectRetry timer expired event, the local system   restarts the ConnectRetry timer, initiates a transport connection to   the TRIP peer, continues to listen for a connection that may be   initiated by the remote TRIP peer, and changes its state to Connect.   If the local LS detects that a remote peer is trying to establish a   connection to it and the IP address of the peer is not an expected   one, then the local LS rejects the attempted connection and continues   to listen for a connection from its expected peers without changing   state.   Start event is ignored in the Active state.   In response to any other event (initiated by either the system or the   operator), the local system releases all TRIP resources associated   with this connection and changes its state to Idle.   OpenSent state:   In this state, an LS has sent an OPEN message to its peer and is   waiting for an OPEN message from its peer.  When an OPEN message is   received, all fields are checked for correctness.  If the TRIP   message header checking or OPEN message checking detects an error   (seeSection 6.2) or a connection collision (seeSection 6.8), the   local system sends a NOTIFICATION message and changes its state to   Idle.   If there are no errors in the OPEN message, TRIP sends a KEEPALIVE   message and sets a KeepAlive timer.  The Hold Timer, which was   originally set to a large value (see above), is replaced with the   negotiated Hold Time value (seeSection 4.2).  If the negotiated Hold   Time value is zero, then the Hold Time timer and KeepAlive timers are   not started.  If the value of the ITAD field is the same as the local   ITAD number, then the connection is an "internal" connection;   otherwise, it is "external" (this will affect UPDATE processing).   Finally, the state is changed to OpenConfirm.   If the local LS detects that a remote peer is trying to establish a   connection to it and the IP address of the peer is not an expected   one, then the local LS rejects the attempted connection and continues   to listen for a connection from its expected peers without changing   state.   If a disconnect notification is received from the underlying   transport protocol, the local LS closes the transport connection,   restarts the ConnectRetry timer, continues to listen for a connection   that may be initiated by the remote TRIP peer, and goes into the   Active state.Rosenberg, et. al.          Standards Track                    [Page 52]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   If the Hold Timer expires, the local LS sends a NOTIFICATION message   with the Error Code "Hold Timer Expired" and changes its state to   Idle.   In response to the Stop event (initiated by either system or   operator) the local LS sends a NOTIFICATION message with the Error   Code "Cease" and changes its state to Idle.   The Start event is ignored in the OpenSent state.   In response to any other event the local LS sends a NOTIFICATION   message with the Error Code "Finite State Machine Error" and changes   its state to Idle.   Whenever TRIP changes its state from OpenSent to Idle, it closes the   transport connection and releases all resources associated with that   connection.   OpenConfirm state:   In this state, an LS has sent an OPEN to its peer, received an OPEN   from its peer, and sent a KEEPALIVE in response to the OPEN.  The LS   is now waiting for a KEEPALIVE or NOTIFICATION message in response to   its OPEN.   If the local LS receives a KEEPALIVE message, it changes its state to   Established.   If the Hold Timer expires before a KEEPALIVE message is received, the   local LS sends NOTIFICATION message with the Error Code "Hold Timer   Expired" and changes its state to Idle.   If the local LS receives a NOTIFICATION message, it changes its state   to Idle.   If the KeepAlive timer expires, the local LS sends a KEEPALIVE   message and restarts its KeepAlive timer.   If a disconnect notification is received from the underlying   transport protocol, the local LS closes the transport connection,   restarts the ConnectRetry timer, continues to listen for a connection   that may be initiated by the remote TRIP peer, and goes into the   Active state.   In response to the Stop event (initiated by either the system or the   operator) the local LS sends NOTIFICATION message with the Error Code   "Cease" and changes its state to Idle.   The Start event is ignored in the OpenConfirm state.Rosenberg, et. al.          Standards Track                    [Page 53]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   In response to any other event the local LS sends a NOTIFICATION   message with the Error Code "Finite State Machine Error" and changes   its state to Idle.   Whenever TRIP changes its state from OpenConfirm to Idle, it closes   the transport connection and releases all resources associated with   that connection.   Established state:   In the Established state, an LS can exchange UPDATE, NOTIFICATION,   and KEEPALIVE messages with its peer.   If the negotiated Hold Timer is zero, then no procedures are   necessary for keeping a peering session alive.  If the negotiated   Hold Time value is non-zero, the procedures of this paragraph apply.   If the Hold Timer expires, the local LS sends a NOTIFICATION message   with the Error Code "Hold Timer Expired" and changes its state to   Idle.  If the KeepAlive Timer expires, then the local LS sends a   KeepAlive message and restarts the KeepAlive Timer.  If the local LS   receives an UPDATE or KEEPALIVE message, then it restarts its Hold   Timer.  Each time the LS sends an UPDATE or KEEPALIVE message, it   restarts its KeepAlive Timer.   If the local LS receives a NOTIFICATION message, it changes its state   to Idle.   If the local LS receives an UPDATE message and the UPDATE message   error handling procedure (see Section6.3) detects an error, the local   LS sends a NOTIFICATION message and changes its state to Idle.   If a disconnect notification is received from the underlying   transport protocol, the local LS changes its state to Idle.   In response to the Stop event (initiated by either the system or the   operator), the local LS sends a NOTIFICATION message with the Error   Code "Cease" and changes its state to Idle.   The Start event is ignored in the Established state.   In response to any other event, the local LS sends a NOTIFICATION   message with Error Code "Finite State Machine Error" and changes its   state to Idle.   Whenever TRIP changes its state from Established to Idle, it closes   the transport connection and releases all resources associated with   that connection.  Additionally, if the peer is an external peer, the   LS deletes all routes derived from that connection.Rosenberg, et. al.          Standards Track                    [Page 54]

RFC 3219            Telephony Routing over IP (TRIP)        January 200210. UPDATE Message Handling   An UPDATE message may be received only in the Established state.   When an UPDATE message is received, each field is checked for   validity as specified inSection 6.3.  The rest of this section   presumes that the UPDATE message has passed the error-checking   procedures ofSection 6.3.   If the UPDATE message was received from an internal peer, the   flooding procedures ofSection 10.1 MUST be applied.  The flooding   process synchronizes the Loc-TRIBs of all LSs within the domain.   Certain routes within the UPDATE may be marked as old or duplicates   by the flooding process and are ignored during the rest of the UPDATE   processing.   If the UPDATE message contains withdrawn routes, then the   corresponding previously advertised routes shall be removed from the   Adj-TRIB-In.  This LS MUST rerun its Decision Process since the   previously advertised route is no longer available for use.   If the UPDATE message contains a route, then the route MUST be placed   in the appropriate Adj-TRIB-In, and the following additional actions   MUST be taken:      1. If its destinations are identical to those of a route currently         stored in the Adj-TRIB-In, then the new route MUST replace the         older route in the Adj-TRIB-In, thus implicitly withdrawing the         older route from service.  The LS MUST rerun its Decision         Process since the older route is no longer available for use.      2. If the new route is more specific than an earlier route         contained in the Adj-TRIB-In and has identical attributes, then         no further actions are necessary.      3. If the new route is more specific than an earlier route         contained in the Adj-TRIB-In but does not have identical         attributes, then the LS MUST run its Decision Process since the         more specific route has implicitly made a portion of the less         specific route unavailable for use.      4. If the new route has destinations that are not present in any         of the routes currently stored in the Adj-TRIB-In, then the LS         MUST run its Decision Process.      5. If the new route is less specific than an earlier route         contained in the Adj-TRIB-In, the LS MUST run its Decision         Process on the set of destinations that are described only by         the less specific route.Rosenberg, et. al.          Standards Track                    [Page 55]

RFC 3219            Telephony Routing over IP (TRIP)        January 200210.1. Flooding Process   When an LS receives an UPDATE message from an internal peer, the LS   floods the new information from that message to all of its other   internal peers.  Flooding is used to efficiently synchronize all of   the LSs within a domain without putting any constraints on the   domain's internal topology.  The flooding mechanism is based on the   techniques used in OSPF [4] and SCSP [6].  One may argue that TRIP's   flooding process is in reality a controlled broadcast mechanism.10.1.1. Database Information   The LS MUST maintain the sequence number and originating TRIP   identifier for each link-state encapsulated attribute in an internal   Adj-TRIB-In.  These values are included with the route in the   ReachableRoutes, WithdrawnRoutes, and ITAD Topology attributes.  The   originating TRIP identifier gives the internal LS that originated   this route into the ITAD, the sequence number gives the version of   this route at the originating LS.10.1.2. Determining Newness   For each route in the ReachableRoutes or WithdrawnRoutes field, the   LS decides if the route is new or old.  This is determined by   comparing the Sequence Number of the route in the UPDATE with the   Sequence Number of the route saved in the Adj-TRIB-In.  The route is   new if either the route does not exist in the Adj-TRIB-In for the   originating LS, or if the route does exist in the Adj-TRIB-In but the   Sequence Number in the UPDATE is greater than the Sequence Number   saved in the Adj-TRIBs-In.  Note that the newness test is   independently applied to each link-state encapsulated attribute in   the UPDATE (WithdrawnRoutes or ReachableRoutes or ITAD Topology).10.1.3. Flooding   Each route in the ReachableRoutes or WithdrawnRoutes field that is   determined to be old is ignored in further processing.  If the route   is determined to be new then the following actions occur.   If the route is being withdrawn, then the LS MUST flood the withdrawn   route to all other internal peers, and MUST mark the route as   withdrawn.  An LS MUST maintain routes marked as withdrawn in its   databases for MaxPurgeTime seconds.   If the route is being updated, then the LS MUST update the route in   the Adj-TRIB-In and MUST flood it to all other internal peers.Rosenberg, et. al.          Standards Track                    [Page 56]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   If these procedures result in changes to the Adj-TRIB-In, then the   route is also made available for local route processing as described   early inSection 10.   To implement flooding, the following is recommended.  All routes   received in a single UPDATE message that are determined to be new   should be forwarded to all other internal peers in a single UPDATE   message.  Other variations of flooding are possible, but the local LS   MUST ensure that each new route (and any associated attributes)   received from an internal peer get forwarded to every other internal   peer.10.1.4. Sequence Number Considerations   The Sequence Number is used to determine when one version of a Route   is newer than another version of a route.  A larger Sequence Number   indicates a newer version.  The Sequence Number is assigned by the LS   originating the route into the local ITAD.  The Sequence Number is an   unsigned 4-octet integer in the range of 1 thru 2^31-1 MinSequenceNum   thru MaxSequenceNum).  The value 0 is reserved.  When an LS first   originates a route (including when the LS restarts/reboots) into its   ITAD, it MUST originate it with a Sequence Number of MinSequenceNum.   Each time the route is updated within the ITAD by the originator, the   Sequence Number MUST be increased.   If it is ever the case that the sequence number is MaxSequenceNum-1   and it needs to be increased, then the TRIP module of the LS MUST be   disabled for a period of TripDisableTime so that all routes   originated by this LS with high sequence numbers can be removed.10.1.5. Purging a Route Within the ITAD   To withdraw a route that it originated within the ITAD, an LS   includes the route in the WithdrawnRoutes field of an UPDATE message.   The Sequence Number MUST be greater than the last valid version of   the route.  The LS MAY choose to use a sequence number of   MaxSequenceNum when withdrawing routes within its ITAD, but this is   not required.   After withdrawing a route, an LS MUST mark the route as "withdrawn"   in its database, and maintain the withdrawn route in its database for   MaxPurgeTime seconds.  If the LS needs to re-originate a route that   had been purged but is still in its database, it can either re-   originate the route immediately using a Sequence Number that is   greater than that used in the withdraw, or the LS may wait until   MaxPurgeTime seconds have expired since the route was withdrawn.Rosenberg, et. al.          Standards Track                    [Page 57]

RFC 3219            Telephony Routing over IP (TRIP)        January 200210.1.6. Receiving Self-Originated Routes   It is common for an LS to receive UPDATES for routes that it   originated within the ITAD via the flooding procedure.  If the LS   receives an UPDATE for a route that it originated that is newer (has   a higher sequence number) than the LSs current version, then special   actions must be taken.  This should be a relatively rare occurrence   and indicates that a route still exists within the ITAD since the LSs   last restart/reboot.   If an LS receives a self-originated route update that is newer than   the current version of the route at the LS, then the following   actions MUST be taken.  If the LS still wishes to advertise the   information in the route, then the LS MUST increase the Sequence   Number of the route to a value greater than that received in the   UPDATE and re-originate the route.  If the LS does not wish to   continue to advertise the route, then it MUST purge the route as   described inSection 10.1.5.10.1.7. Removing Withdrawn Routes   An LS SHOULD ensure that routes marked as withdrawn are removed from   the database in a timely fashion after the MaxPurgeTime has expired.   This could be done, for example, by periodically sweeping the   database, and deleting those entries that were withdrawn more than   MaxPurgeTime seconds ago.10.2. Decision Process   The Decision Process selects routes for subsequent advertisement by   applying the policies in the local Policy Information Base (PIB) to   the routes stored in its Adj-TRIBs-In.  The output of the Decision   process is the set of routes that will be advertised to all peers;   the selected routes will be stored in the local LS's Adj-TRIBs-Out.   The selection process is formalized by defining a function that takes   the attributes of a given route as an argument and returns a non-   negative integer denoting the degree of preference for the route.   The function that calculates the degree of preference for a given   route shall not use as its inputs any of the following:  the   existence of other routes, the non-existence of other routes, or the   attributes of other routes.  Route selection then consists of an   individual application of the degree of preference function to each   feasible route, followed by the choice of the one with the highest   degree of preference.Rosenberg, et. al.          Standards Track                    [Page 58]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   All internal LSs in an ITAD MUST run the Decision Process and apply   the same decision criteria, otherwise it will not be possible to   synchronize their Loc-TRIBs.   The Decision Process operates on routes contained in each Adj-TRIBs-   In, and is responsible for:      -  selection of routes to be advertised to internal peers      -  selection of routes to be advertised to external peers      -  route aggregation and route information reduction   The Decision Process takes place in three distinct phases, each   triggered by a different event:      -  Phase 1 is responsible for calculating the degree of preference         for each route received from an external peer.      -  Phase 2 is invoked on completion of phase 1.  It is responsible         for choosing the best route out of all those available for each         distinct destination, and for installing each chosen route into         the Loc-TRIB.      -  Phase 3 is invoked after the Loc-TRIB has been modified.  It is         responsible for disseminating routes in the Loc-TRIB to each         external peer, according to the policies contained in the PIB.         Route aggregation and information reduction can optionally be         performed within this phase.10.2.1. Phase 1: Calculation of Degree of Preference   The Phase 1 decision function shall be invoked whenever the local LS   receives from a peer an UPDATE message that advertises a new route, a   replacement route, or a withdrawn route.   The Phase 1 decision function is a separate process that is completed   when it has no further work to do.   The Phase 1 decision function shall lock an Adj-TRIB-In prior to   operating on any route contained within it, and shall unlock it after   operating on all new or replacement routes contained within it.   The local LS MUST determine a degree of preference for each newly   received or replacement route.  If the route is learned from an   internal peer, the value of the LocalPreference attribute MUST be   taken as the degree of preference.  If the route is learned from an   external peer, then the degree of preference MUST be computed based   on pre-configured policy information and used as the LocalPreference   value in any intra-domain TRIP advertisement.  The exact nature of   this policy information and the computation involved is a local   matter.Rosenberg, et. al.          Standards Track                    [Page 59]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   The output of the degree of preference determination process is the   local preference of a route.  The local LS computes the local   preference of routes learned from external peers or originated   internally at that LS.  The local preference of a route learned from   an internal peer is included in the LocalPreference attribute   associated with that route.10.2.2. Phase 2: Route Selection   The Phase 2 decision function shall be invoked on completion of Phase   1.  The Phase 2 function is a separate process that completes when it   has no further work to do.  Phase 2 consists of two sub-phases: 2a   and 2b.  The same route selection function is applied in both sub-   phases, but the inputs to each phase are different.  The Phase 2a   process MUST consider as inputs all external routes, that are present   in the Adj-TRIBs-In of external peers, and all local routes.  The   output of Phase 2a is inserted into the Ext-TRIB.  The Phase 2b   process shall be invoked upon completion of Phase 2a and it MUST   consider as inputs all routes in the Ext-TRIB and all routes that are   present in the Adj-TRIBs-In of internal LSs.  The output of Phase 2b   is stored in the Loc-TRIB.   The Phase 2 decision function MUST be blocked from running while the   Phase 3 decision function is in process.  The Phase 2 function MUST   lock all Adj-TRIBs-In and the Ext-TRIB prior to commencing its   function, and MUST unlock them on completion.   If the LS determines that the NextHopServer listed in a route is   unreachable, then the route MAY be excluded from the Phase 2 decision   function.  The means by which such a determination is made is not   mandated here.   For each set of destinations for which one or more routes exist, the   local LS's route selection function MUST identify the route that has:      -  the highest degree of preference, or      -  is selected as a result of the tie breaking rules specified in         10.2.2.1.   Withdrawn routes MUST be removed from the Loc-TRIB, Ext-TRIB, and the   Adj-TRIBs-In.10.2.2.1. Breaking Ties (Phase 2)   Several routes to the same destination that have the same degree of   preference may be input to the Phase 2 route selection function.  The   local LS can select only one of these routes for inclusion in theRosenberg, et. al.          Standards Track                    [Page 60]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   associated Ext-TRIB (Phase 2a) or Loc-TRIB (Phase 2b).  The local LS   considers all routes with the same degrees of preference.  The   following algorithm shall be used to break ties.      -  If the local LS is configured to use the MultiExitDisc         attribute to break ties, and candidate routes received from the         same neighboring ITAD differ in the value of the MultiExitDisc         attribute, then select the route that has the larger value of         MultiExitDisc.      -  If at least one of the routes was originated by an internal LS,         select the route route that was advertised by the internal LS         that has the lowest TRIP ID.      -  Otherwise, select the route that was advertised by the neighbor         domain that has the lowest ITAD number.10.2.3. Phase 3: Route Dissemination   The Phase 3 decision function MUST be invoked upon completion of   Phase 2 if Phase 2 results in changes to the Loc-TRIB or when a new   LS-to-LS peer session is established.   The Phase 3 function is a separate process that is completed when it   has no further work to do.  The Phase 3 routing decision function   MUST be blocked from running while the Phase 2 decision function is   in process.   All routes in the Loc-TRIB shall be processed into a corresponding   entry in the associated Adj-TRIBs-Out.  Route aggregation and   information reduction techniques (see 10.3.4) MAY optionally be   applied.   When the updating of the Adj-TRIBs-Out is complete, the local LS MUST   run the external update process of 10.3.2.10.2.4. Overlapping Routes   When overlapping routes are present in the same Adj-TRIB-In, the more   specific route shall take precedence, in order, from most specific to   least specific.   The set of destinations described by the overlap represents a portion   of the less specific route that is feasible, but is not currently in   use.  If a more specific route is later withdrawn, the set of   destinations described by the more specific route will still be   reachable using the less specific route.Rosenberg, et. al.          Standards Track                    [Page 61]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   If an LS receives overlapping routes, the Decision Process MUST take   into account the semantics of the overlapping routes.  In particular,   if an LS accepts the less specific route while rejecting the more   specific route from the same peer, then the destinations represented   by the overlap may not forward along the domains listed in the   AdvertisementPath attribute of that route.  Therefore, an LS has the   following choices:      1. Install both the less and the more specific routes      2. Install the more specific route only      3. Install the non-overlapping part of the less specific route         only (that implies disaggregation of the less-specific route)      4. Aggregate the two routes and install the aggregated route      5. Install the less specific route only      6. Install neither route   If an LS chooses 5), then it SHOULD add AtomicAggregate attribute to   the route.  A route that carries AtomicAggregate attribute MUST NOT   be de-aggregated.  That is, the route cannot be made more specific.   Forwarding along such a route does not guarantee that route traverses   only domains listed in the RoutedPath of the route.  If an LS chooses   1), then it MUST NOT advertise the less specific route without the   more specific route.10.3. Update-Send Process   The Update-Send process is responsible for advertising UPDATE   messages to all peers.  For example, it distributes the routes chosen   by the Decision Process to other LSs that may be located in either   the same ITAD or a neighboring ITAD.  Rules for information exchange   between peer LSs located in different ITADs are given in 10.3.2;   rules for information exchange between peer LSs located in the same   ITAD are given in 10.3.1.   Before forwarding routes to peers, an LS MUST determine which   attributes should be forwarded along with that route.  If a not   well-known non-transitive attribute is unrecognized, it is quietly   ignored.  If a not well-known dependent-transitive attribute is   unrecognized, and the NextHopServer attribute has been changed by the   LS, the unrecognized attribute is quietly ignored.  If a not well-   known dependent-transitive attribute is unrecognized, and the   NextHopServer attribute has not been modified by the LS, the Partial   bit in the attribute flags octet is set to 1, and the attribute is   retained for propagation to other TRIP speakers.  Similarly, if an   not well-known independent-transitive attribute is unrecognized, the   Partial bit in the attribute flags octet is set to 1, and the   attribute is retained for propagation to other TRIP speakers.Rosenberg, et. al.          Standards Track                    [Page 62]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   If a not well-known attribute is recognized, and has a valid value,   then, depending on the type of the not well-known attribute, it is   updated, if necessary, for possible propagation to other TRIP   speakers.10.3.1. Internal Updates   The Internal update process is concerned with the distribution of   routing information to internal peers.   When an LS receives an UPDATE message from another TRIP LS located in   its own ITAD, it is flooded as described inSection 10.1.   When an LS receives a new route from an LS in a neighboring ITAD, or   if a local route is injected into TRIP, the LS determines the   preference of that route.  If the new route has the highest degree of   preference for all external routes and local routes to a given   destination (or if the route was selected via a tie-breaking   procedure as specified in 10.3.1.1), the LS MUST insert that new   route into the Ext-TRIB database and the LS MUST advertise that route   to all other LSs in its ITAD by means of an UPDATE message.  The LS   MUST advertise itself as the Originator of that route within the   ITAD.   When an LS receives an UPDATE message with a non-empty   WithdrawnRoutes attribute from an external peer, or if a local route   is withdrawn from TRIP, the LS MUST remove from its Adj-TRIB-In all   routes whose destinations were carried in this field.  If the   withdrawn route was previously selected into the Ext-TRIB, the LS   MUST take the following additional steps:      -  If a new route is selected for advertisement for those         destinations, then the LS MUST insert the replacement route         into Ext-TRIB to replace the withdrawn route and advertise it         to all internal LSs.      -  If a replacement route is not available for advertisement, then         the LS MUST include the destinations of the route in the         WithdrawnRoutes attribute of an UPDATE message, and MUST send         this message to each internal peer.  The LS MUST also remove         the withdrawn route from the Ext-TRIB.10.3.1.1. Breaking Ties (Routes Received from External Peers)   If an LS has connections to several external peers, there will be   multiple Adj-TRIBs-In associated with these peers.  These databases   might contain several equally preferable routes to the sameRosenberg, et. al.          Standards Track                    [Page 63]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   destination, all of which were advertised by external peers.  The   local LS shall select one of these routes according to the following   rules:      -  If the LS is configured to use the MultiExitDisc attribute to         break ties, and the candidate routes differ in the value of the         MultiExitDisc attribute, then select the route that has the         lowest value of MultiExitDisc, else      -  Select the route that was advertised by the external LS that         has the lowest TRIP Identifier.10.3.2. External Updates   The external update process is concerned with the distribution of   routing information to external peers.  As part of the Phase 3 route   selection process, the LS has updated its Adj-TRIBs-Out.  All newly   installed routes and all newly unfeasible routes for which there is   no replacement route MUST be advertised to external peers by means of   UPDATE messages.   Any routes in the Loc-TRIB marked as withdrawn MUST be removed.   Changes to the reachable destinations within its own ITAD SHALL also   be advertised in an UPDATE message.10.3.3. Controlling Routing Traffic Overhead   The TRIP protocol constrains the amount of routing traffic (that is,   UPDATE messages) in order to limit both the link bandwidth needed to   advertise UPDATE messages and the processing power needed by the   Decision Process to digest the information contained in the UPDATE   messages.10.3.3.1. Frequency of Route Advertisement   The parameter MinRouteAdvertisementInterval determines the minimum   amount of time that must elapse between advertisements of routes to a   particular destination from a single LS.  This rate limiting   procedure applies on a per-destination basis, although the value of   MinRouteAdvertisementInterval is set on a per LS peer basis.   Two UPDATE messages sent from a single LS that advertise feasible   routes to some common set of destinations received from external   peers MUST be separated by at least MinRouteAdvertisementInterval.   Clearly, this can only be achieved precisely by keeping a separate   timer for each common set of destinations.  This would be unwarranted   overhead.  Any technique which ensures that the interval between two   UPDATE messages sent from a single LS that advertise feasible routesRosenberg, et. al.          Standards Track                    [Page 64]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   to some common set of destinations received from external peers will   be at least MinRouteAdvertisementInterval, and will also ensure that   a constant upper bound on the interval is acceptable.   Two UPDATE messages, sent from a single LS to an external peer, that   advertise feasible routes to some common set of destinations received   from internal peers MUST be separated by at least   MinRouteAdvertisementInterval.   Since fast convergence is needed within an ITAD, this rate limiting   procedure does not apply to routes received from internal peers and   being broadcast to other internal peers.  To avoid long-lived black   holes, the procedure does not apply to the explicit withdrawal of   routes (that is, routes whose destinations explicitly withdrawn by   UPDATE messages).   This procedure does not limit the rate of route selection, but only   the rate of route advertisement.  If new routes are selected multiple   times while awaiting the expiration of MinRouteAdvertisementInterval,   the last route selected shall be advertised at the end of   MinRouteAdvertisementInterval.10.3.3.2. Frequency of Route Origination   The parameter MinITADOriginationInterval determines the minimum   amount of time that must elapse between successive advertisements of   UPDATE messages that report changes within the advertising LS's own   ITAD.10.3.3.3. Jitter   To minimize the likelihood that the distribution of TRIP messages by   a given LS will contain peaks, jitter should be applied to the timers   associated with MinITADOriginationInterval, KeepAlive, and   MinRouteAdvertisementInterval.  A given LS shall apply the same   jitter to each of these quantities regardless of the destinations to   which the updates are being sent; that is, jitter will not be applied   on a "per peer" basis.   The amount of jitter to be introduced shall be determined by   multiplying the base value of the appropriate timer by a random   factor that is uniformly distributed in the range from 0.75 to 1.0.Rosenberg, et. al.          Standards Track                    [Page 65]

RFC 3219            Telephony Routing over IP (TRIP)        January 200210.3.4. Efficient Organization of Routing Information   Having selected the routing information that it will advertise, a   TRIP speaker may use methods to organize this information in an   efficient manner.  These methods are discussed in the following   sections.10.3.4.1. Information Reduction   Information reduction may imply a reduction in granularity of policy   control - after information has collapsed, the same policies will   apply to all destinations and paths in the equivalence class.   The Decision Process may optionally reduce the amount of information   that it will place in the Adj-TRIBs-Out by any of the following   methods:      -  ReachableRoutes: A set of destinations can be usually         represented in compact form.  For example, a set of E.164 phone         numbers can be represented in more compact form using E.164         prefixes.      -  AdvertisementPath: AdvertisementPath information can be         represented as ordered AP_SEQUENCEs or unordered AP_SETs.         AP_SETs are used in the route aggregation algorithm described         inSection 5.4.4.  They reduce the size of the AP_PATH         information by listing each ITAD number only once, regardless         of how many times it may have appeared in multiple         advertisement paths that were aggregated.   An AP_SET implies that the destinations advertised in the UPDATE   message can be reached through paths that traverse at least some of   the constituent ITADs.  AP_SETs provide sufficient information to   avoid route looping; however their use may prune potentially feasible   paths, since such paths are no longer listed individually as in the   form of AP_SEQUENCEs.  In practice this is not likely to be a   problem, since once a call arrives at the edge of a group of ITADs,   the LS at that point is likely to have more detailed path information   and can distinguish individual paths to destinations.10.3.4.2. Aggregating Routing Information   Aggregation is the process of combining the characteristics of   several different routes in such a way that a single route can be   advertised.  Aggregation can occur as part of the decision process to   reduce the amount of routing information that is placed in the Adj-   TRIBs-Out.Rosenberg, et. al.          Standards Track                    [Page 66]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   Aggregation reduces the amount of information an LS must store and   exchange with other LSs.  Routes can be aggregated by applying the   following procedure separately to attributes of like type.   Routes that have the following attributes shall not be aggregated   unless the corresponding attributes of each route are identical:   MultiExitDisc, NextHopServer.   Attributes that have different type codes cannot be aggregated.   Attributes of the same type code may be aggregated.  The rules for   aggregating each attribute MUST be provided together with attribute   definition.  For example, aggregation rules for TRIP's basic   attributes, e.g., ReachableRoutes and AdvertisementPath, are given inSection 5.10.4. Route Selection Criteria   Generally speaking, additional rules for comparing routes among   several alternatives are outside the scope of this document.  There   are two exceptions:      -  If the local ITAD appears in the AdvertisementPath of the new         route being considered, then that new route cannot be viewed as         better than any other route.  If such a route were ever used, a         routing loop could result (seeSection 6.3).      -  In order to achieve successful distributed operation, only         routes with a likelihood of stability can be chosen.  Thus, an         ITAD must avoid using unstable routes, and it must not make         rapid spontaneous changes to its choice of route.  Quantifying         the terms "unstable" and "rapid" in the previous sentence will         require experience, but the principle is clear.10.5. Originating TRIP Routes   An LS may originate local routes by injecting routing information   acquired by some other means (e.g. via an intra-domain routing   protocol or through manual configuration or some dynamic registration   mechanism/protocol) into TRIP.  An LS that originates TRIP routes   shall assign the degree of preference to these routes by passing them   through the Decision Process (seeSection 10.2).  To TRIP, local   routes are identical to external routes and are subjected to the same   two phase route selection mechanism.  A local route which is selected   into the Ext-TRIB MUST be advertised to all internal LSs.  The   decision whether to distribute non-TRIP acquired routes within an   ITAD via TRIP or not depends on the environment within the ITAD (e.g.   type of intra-domain routing protocol) and should be controlled via   configuration.Rosenberg, et. al.          Standards Track                    [Page 67]

RFC 3219            Telephony Routing over IP (TRIP)        January 200211. TRIP Transport   This specification defines the use of TCP as the transport layer for   TRIP.  TRIP uses TCP port 6069.  Running TRIP over other transport   protocols is for further study.12. ITAD Topology   There are no restrictions on the intra-domain topology of TRIP LSs.   For example, LSs in an ITAD can be configured in a full mesh, star,   or any other connected topology.  Similarly, there are no   restrictions on the topology of TRIP ITADs.  For example, the ITADs   can be organized in a flat topology (mesh or ring) or in multi-level   hierarchy or any other topology.   The border between two TRIP ITADs may be located either on the link   between two TRIP LSs or it may coincide on a TRIP LS.  In the latter   case, the same TRIP LS will be member in more than one ITAD, and it   appears to be an internal peer to LSs in each ITAD it is member of.13. IANA Considerations   This document creates a new IANA registry for TRIP parameters.  The   following TRIP parameters are included in the registry:      - TRIP Capabilities      - TRIP Attributes      - TRIP Address Families      - TRIP Application Protocols      - TRIP ITAD Numbers   Protocol parameters are frequently initialized/reset to 0.  This   document reserves the value 0 of each of the above TRIP parameters in   order to clearly distinguish between an unset parameter and any other   registered values for that parameter.   The sub-registries for each of the above parameters are discussed in   the sections below.13.1. TRIP Capabilities   Requests to add TRIP capabilities other than those defined inSection4.2.1.1 must be submitted to iana@iana.org.  Following the assigned   number policies outlined in [11], Capability Codes in the range   32768-65535 are reserved for Private Use (these are the codes with   the first bit of the code value equal to 1).  This document reserves   value 0.  Capability Codes 1 and 2 have been assigned inSection4.2.1.1.  Capability Codes in the range 2-32767 are controlled byRosenberg, et. al.          Standards Track                    [Page 68]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   IANA, and are allocated subject to the Specification Required (IETF   RFC or equivalent) condition.  The specification MUST include a   description of the capability, the possible values it may take, and   what constitutes a capability mismatch.13.2. TRIP Attributes   This document reserves Attribute Type Codes 224-255 for Private Use   (these are the codes with the first three bits of the code equal to   1).  This document reserves the value 0.  Attribute Type Codes 1   through 11 have already been allocated by this document.  Attribute   Type Codes 1 through 11 are defined in Sections5.1 through5.11.   Attribute Type Codes in the range 12-223 are controlled by IANA, and   require a Specification document (RFC or equivalent).  The   specification MUST provide all information required inSection 5.12   of this document.   Attribute Type Code registration requests must be sent to   iana@iana.org.  In addition to the specification requirement, the   request MUST include an indication of who has change control over the   attribute and contact information (postal and email address).13.3. Destination Address Families   This document reserves address family 0. Requests to add TRIP address   families other than those defined inSection 5.1.1.1 ( address   families 1, 2, and 3), i.e., in the range 4-32767, must be submitted   to iana@iana.org.  The request MUST include a brief description of   the address family, its alphabet, and special processing rules and   guidelines, such as guidelines for aggregation, if any.  The requests   are subject to Expert Review.  This document reserves the address   family codes 32768-65535 for vendor-specific applications.13.4. TRIP Application Protocols   This document creates a new IANA registry for TRIP application   protocols.  This document reserves the application protocol code 0.   Requests to add TRIP application protocols other than those defined   inSection 5.1.1.1 (application protocols 1 through 4), i.e., in the   range 5-32767, must be submitted to iana@iana.org.  The request MUST   include a brief background on the application protocol, and a   description of how TRIP can be used to advertise routes for that   protocol.  The requests are subject to Expert Review.  This document   reserves the application protocol codes 32768-65535 for vendor-   specific applications.Rosenberg, et. al.          Standards Track                    [Page 69]

RFC 3219            Telephony Routing over IP (TRIP)        January 200213.5. ITAD Numbers   This document reserves the ITAD number 0.  ITAD numbers in the range   1-255 are designated for Private Use.  ITAD numbers in the range from   256 to (2**32)-1 are allocated by IANA on a First-Come-First-Serve   basis.  Requests for ITAD numbers must be submitted to iana@iana.org.   The requests MUST include the following:      -  Information about the organization that will administer the         ITAD.      -  Contact information (postal and email address).14. Security Considerations   This section covers security between peer TRIP LSs when TRIP runs   over TCP in an IP environment.   A security mechanism is clearly needed to prevent unauthorized   entities from using the protocol defined in this document for setting   up unauthorized peer sessions with other TRIP LSs or interfering with   authorized peer sessions.  The security mechanism for the protocol,   when transported over TCP in an IP network, is IPsec [12].  IPsec   uses two protocols to provide traffic security: Authentication Header   (AH) [13] and Encapsulating Security Payload (ESP) [14].   The AH header affords data origin authentication, connectionless   integrity and optional anti-replay protection of messages passed   between the peer LSs.  The ESP header provides origin authentication,   connectionless integrity, anti-replay protection, and confidentiality   of messages.   Implementations of the protocol defined in this document employing   the ESP header SHALL comply with section 5 of [14], which defines a   minimum set of algorithms for integrity checking and encryption.   Similarly, implementations employing the AH header SHALL comply with   section 5 of [13], which defines a minimum set of algorithms for   integrity checking using manual keys.   Implementations SHOULD use IKE [15] to permit more robust keying   options.  Implementations employing IKE SHOULD support authentication   with RSA signatures and RSA public key encryption.   A Security Association (SA) [12] is a simplex "connection" that   affords security services to the traffic carried by it.  Security   services are afforded to a SA by the use of AH, or ESP, but not both.   Two types of SAs are defined: transport mode and tunnel mode [12].  A   transport mode SA is a security association between two hosts, and is   appropriate for protecting the TRIP session between two peer LSs.Rosenberg, et. al.          Standards Track                    [Page 70]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002A1. Appendix 1: TRIP FSM State Transitions and Actions   This Appendix discusses the transitions between states in the TRIP   FSM in response to TRIP events.  The following is the list of these   states and events when the negotiated Hold Time value is non-zero.   TRIP States:      1 - Idle      2 - Connect      3 - Active      4 - OpenSent      5 - OpenConfirm      6 - Established   TRIP Events:      1 - TRIP Start      2 - TRIP Stop      3 - TRIP Transport connection open      4 - TRIP Transport connection closed      5 - TRIP Transport connection open failed      6 - TRIP Transport fatal error      7 - ConnectRetry timer expired      8 - Hold Timer expired      9 - KeepAlive timer expired      10 - Receive OPEN message      11 - Receive KEEPALIVE message      12 - Receive UPDATE messages      13 - Receive NOTIFICATION message   The following table describes the state transitions of the TRIP FSM   and the actions triggered by these transitions.   Event                Actions              Message Sent    Next State   --------------------------------------------------------------------   Idle (1)    1            Initialize resources            none             2                 Start ConnectRetry timer                 Initiate a transport connection    others               none                    none             1   Connect(2)    1                    none                    none             2    3            Complete initialization         OPEN             4                 Clear ConnectRetry timer    5            Restart ConnectRetry timer      none             3    7            Restart ConnectRetry timer      none             2                 Initiate a transport connection    others       Release resources               none             1Rosenberg, et. al.          Standards Track                    [Page 71]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   Active (3)    1                    none                    none             3    3            Complete initialization         OPEN             4                 Clear ConnectRetry timer    5            Close connection                                 3                 Restart ConnectRetry timer    7            Restart ConnectRetry timer      none             2                 Initiate a transport connection    others       Release resources               none             1   OpenSent(4)    1                    none                    none             4    4            Close transport connection      none             3                 Restart ConnectRetry timer    6            Release resources               none             1   10            Process OPEN is OK            KEEPALIVE          5                 Process OPEN failed           NOTIFICATION       1   others        Close transport connection    NOTIFICATION       1                 Release resources   OpenConfirm (5)    1                   none                     none             5    4            Release resources               none             1    6            Release resources               none             1    9            Restart KeepAlive timer       KEEPALIVE          5   11            Complete initialization         none             6                 Restart Hold Timer   13            Close transport connection                       1                 Release resources   others        Close transport connection    NOTIFICATION       1                 Release resources   Established (6)    1                   none                     none             6    4            Release resources               none             1    6            Release resources               none             1    9            Restart KeepAlive timer       KEEPALIVE          6   11            Restart Hold Timer              none             6   12            Process UPDATE is OK          UPDATE             6                 Process UPDATE failed         NOTIFICATION       1   13            Close transport connection                       1                 Release resources   others        Close transport connection    NOTIFICATION       1                 Release resources   -----------------------------------------------------------------Rosenberg, et. al.          Standards Track                    [Page 72]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   The following is a condensed version of the above state transition   table.   Events| Idle | Connect | Active | OpenSent | OpenConfirm | Estab         | (1)  |   (2)   |  (3)   |    (4)   |     (5)     |   (6)         |----------------------------------------------------------    1    |  2   |    2    |   3    |     4    |      5      |    6         |      |         |        |          |             |    2    |  1   |    1    |   1    |     1    |      1      |    1         |      |         |        |          |             |    3    |  1   |    4    |   4    |     1    |      1      |    1         |      |         |        |          |             |    4    |  1   |    1    |   1    |     3    |      1      |    1         |      |         |        |          |             |    5    |  1   |    3    |   3    |     1    |      1      |    1         |      |         |        |          |             |    6    |  1   |    1    |   1    |     1    |      1      |    1         |      |         |        |          |             |    7    |  1   |    2    |   2    |     1    |      1      |    1         |      |         |        |          |             |    8    |  1   |    1    |   1    |     1    |      1      |    1         |      |         |        |          |             |    9    |  1   |    1    |   1    |     1    |      5      |    6         |      |         |        |          |             |   10    |  1   |    1    |   1    |  1 or 5  |      1      |    1         |      |         |        |          |             |   11    |  1   |    1    |   1    |     1    |      6      |    6         |      |         |        |          |             |   12    |  1   |    1    |   1    |     1    |      1      | 1 or 6         |      |         |        |          |             |   13    |  1   |    1    |   1    |     1    |      1      |    1         |      |         |        |          |             |         --------------------------------------------------------------A2. Appendix 2: Implementation Recommendations   This section presents some implementation recommendations.A.2.1: Multiple Networks Per Message   The TRIP protocol allows for multiple address prefixes with the same   advertisement path and next-hop server to be specified in one   message.  Making use of this capability is highly recommended.  With   one address prefix per message there is a substantial increase in   overhead in the receiver.  Not only does the system overhead increase   due to the reception of multiple messages, but the overhead of   scanning the routing table for updates to TRIP peers is incurred   multiple times as well.  One method of building messages containingRosenberg, et. al.          Standards Track                    [Page 73]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   many address prefixes per advertisement path and next hop from a   routing table that is not organized per advertisement path is to   build many messages as the routing table is scanned.  As each address   prefix is processed, a message for the associated advertisement path   and next hop is allocated, if it does not exist, and the new address   prefix is added to it.  If such a message exists, the new address   prefix is just appended to it.  If the message lacks the space to   hold the new address prefix, it is transmitted, a new message is   allocated, and the new address prefix is inserted into the new   message.  When the entire routing table has been scanned, all   allocated messages are sent and their resources released.  Maximum   compression is achieved when all the destinations covered by the   address prefixes share the same next hop server and common   attributes, making it possible to send many address prefixes in one   4096-byte message.   When peering with a TRIP implementation that does not compress   multiple address prefixes into one message, it may be necessary to   take steps to reduce the overhead from the flood of data received   when a peer is acquired or a significant network topology change   occurs.  One method of doing this is to limit the rate of updates.   This will eliminate the redundant scanning of the routing table to   provide flash updates for TRIP peers.  A disadvantage of this   approach is that it increases the propagation latency of routing   information.  By choosing a minimum flash update interval that is not   much greater than the time it takes to process the multiple messages,   this latency should be minimized.  A better method would be to read   all received messages before sending updates.A.2.2: Processing Messages on a Stream Protocol   TRIP uses TCP as a transport mechanism.  Due to the stream nature of   TCP, all the data of a received message does not necessarily arrive   at the same time.  This can make it difficult to process the data as   messages, especially on systems where it is not possible to determine   how much data has been received but not yet processed.   One method that can be used in this situation is to first try to read   just the message header.  For the KEEPALIVE message type, this is a   complete message; for other message types, the header should first be   verified, in particular the total length.  If all checks are   successful, the specified length, minus the size of the message   header is the amount of data left to read.  An implementation that   would "hang" the routing information process while trying to read   from a peer could set up a message buffer (4096 bytes) per peer and   fill it with data as available until a complete message has been   received.Rosenberg, et. al.          Standards Track                    [Page 74]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002A.2.3: Reducing Route Flapping   To avoid excessive route flapping an LS which needs to withdraw a   destination and send an update about a more specific or less specific   route SHOULD combine them into the same UPDATE message.A.2.4: TRIP Timers   TRIP employs seven timers: ConnectRetry, Hold Time, KeepAlive,   MaxPurgeTime, TripDisableTime, MinITADOriginationInterval, and   MinRouteAdvertisementInterval.  The suggested value for the   ConnectRetry timer is 120 seconds.  The suggested value for the Hold   Time is 90 seconds.  The suggested value for the KeepAlive timer is   30 seconds.  The suggested value for the MaxPurgeTime timer is 10   seconds.  The suggested value for the TripDisableTime timer is 180   seconds.  The suggested value for the MinITADOriginationInterval is   30 seconds.  The suggested value for the   MinRouteAdvertisementInterval is 30 seconds.   An implementation of TRIP MUST allow these timers to be configurable.A.2.5: AP_SET Sorting   Another useful optimization that can be done to simplify this   situation is to sort the ITAD numbers found in an AP_SET.  This   optimization is entirely optional.Acknowledgments   We wish to thank Dave Oran for his insightful comments and   suggestions.References   [1]   Bradner, S., "Keywords for use in RFCs to Indicate Requirement         Levels",BCP 14,RFC 2119, March 1997.   [2]   Rosenberg, J. and H. Schulzrinne, "A Framework for a Gateway         Location Protocol",RFC 2871, June 2000.   [3]   Rekhter, Y. and T. Li, "Border Gateway Protocol 4 (BGP-4),"RFC1771, March 1995.   [4]   Moy, J., "Open Shortest Path First Version 2", STD 54,RFC2328, April 1998.Rosenberg, et. al.          Standards Track                    [Page 75]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002   [5]   "Intermediate System to Intermediate System Intra-Domain         Routing Exchange Protocol for use in Conjunction with the         Protocol for Providing the Connectionless-mode Network Service         (ISO 8473)," ISO DP 10589, February 1990.   [6]   Luciani, J., Armitage, G., Halpern, J. and N. Doraswamy,         "Server Cache Synchronization Protocol (SCSP)",RFC 2334, April         1998.   [7]   International Telecommunication Union, "Packet-Based Multimedia         Communication Systems," Recommendation H.323, Version 3         Telecommunication Standardization Sector of ITU, Geneva,         Switzerland, November 2000.   [8]   Handley, H., Schulzrinne, H., Schooler, E. and J. Rosenberg,         "SIP:  Session Initiation Protocol",RFC 2543, March 1999.   [9]   Braden, R., "Requirements for Internet Hosts -- Application and         Support", STD 3,RFC 1123, October 1989.   [10]  Hinden, R. and S. Deering, "IP Version 6 Addressing         Architecture",RFC 2373, July 1998.   [11]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA         Considerations Section in RFCs",BCP 26,RFC 2434, October         1998.   [12]  Kent, S. and R. Atkinson, "Security Architecture for the         Internet Protocol",RFC 2401, November 1998.   [13]  Kent, S. and R. Atkinson, "IP Authentication Header",RFC 2402,         November 1998.   [14]  Kent, S. and R. Atkinson, "IP Encapsulating Security Payload         (ESP)",RFC 2406, November 1998.   [15]  Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",RFC 2409, November 1998.Rosenberg, et. al.          Standards Track                    [Page 76]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002Intellectual Property Notice   The IETF takes no position regarding the validity or scope of any   intellectual property or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; neither does it represent that it   has made any effort to identify any such rights.  Information on the   IETF's procedures with respect to rights in standards-track and   standards-related documentation can be found inBCP 11.  Copies of   claims of rights made available for publication and any assurances of   licenses to be made available, or the result of an attempt made to   obtain a general license or permission for the use of such   proprietary rights by implementers or users of this specification can   be obtained from the IETF Secretariat.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights which may cover technology that may be required to practice   this standard.  Please address the information to the IETF Executive   Director.   The IETF has been notified of intellectual property rights claimed in   regard to some or all of the specification contained in this   document.  For more information consult the online list of claimed   rights.Rosenberg, et. al.          Standards Track                    [Page 77]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002Authors' Addresses   Jonathan Rosenberg   dynamicsoft   72 Eagle Rock Avenue   First Floor   East Hanover, NJ 07936   Phone: 973-952-5000   EMail: jdrosen@dynamicsoft.com   Hussein F. Salama   Cisco Systems   170 W. Tasman Drive   San Jose, CA 95134   Phone: 408-527-7147   EMail: hsalama@cisco.com   Matt Squire   Hatteras Networks   639 Davis Drive   Suite 200   Durham, NC 27713   EMail: mattsquire@acm.orgRosenberg, et. al.          Standards Track                    [Page 78]

RFC 3219            Telephony Routing over IP (TRIP)        January 2002Full Copyright Statement   Copyright (C) The Internet Society (2002).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Rosenberg, et. al.          Standards Track                    [Page 79]