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Network Working Group                                     C. RichardsRequest for Comments: 2125                          Shiva CorporationCategory: Standards Track                                    K. Smith                                          Ascend Communications, Inc.                                                           March 1997The PPP Bandwidth Allocation Protocol (BAP)The PPP Bandwidth Allocation Control Protocol (BACP)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.Abstract   This document proposes a method to manage the dynamic bandwidth   allocation of implementations supporting the PPP multilink protocol   [2].  This is done by defining the Bandwidth Allocation Protocol   (BAP), as well as its associated control protocol, the Bandwidth   Allocation Control Protocol (BACP).  BAP can be used to manage the   number of links in a multilink bundle.  BAP defines datagrams to co-   ordinate adding and removing individual links in a multilink bundle,   as well as specifying which peer is responsible for which decisions   regarding managing bandwidth during a multilink connection.Table of Contents1.     Introduction ..........................................21.1       Specification of Requirements ...................21.2       Terminology .....................................32.     New LCP Configuration Option ..........................32.1       Link Discriminator ..............................33.     BACP Operation ........................................44.     BACP Configuration Options ............................54.1       Favored-Peer ....................................55.     BAP Operation .........................................75.1       Link Management .................................75.2       Bandwidth Management ............................85.3       BAP Packets .....................................85.4       Race Conditions .................................95.5       BAP Datagram Format .............................95.5.1  Call-Request ....................................125.5.2  Call-Response ...................................12Richards & Smith            Standards Track                     [Page 1]

RFC 2125                       PPP BACP                       March 19975.5.3  Callback-Request ................................135.5.4  Callback-Response ...............................135.5.5  Link-Drop-Query-Request .........................135.5.6  Link-Drop-Query-Response ........................135.5.7  Call-Status-Indication ..........................145.5.8  Call-Status-Response ............................146.     BAP Datagram Options ..................................146.1       Link-Type .......................................156.2       Phone-Delta .....................................176.2.1  Phone-Delta Sub-Options .........................186.3       No-Phone-Number-Needed ..........................196.4       Reason ..........................................206.5       Link-Discriminator ..............................216.6       Call-Status .....................................21   Appendix - List of BAP datagrams and associated fields .......23   ACKNOWLEDEMENTS ..............................................23   SECURITY CONSIDERATIONS ......................................23   REFERENCES ...................................................24   CHAIR'S ADDRESS ..............................................24   EDITORS'S ADDRESSES ..........................................241.  Introduction   As PPP multilink implementations become increasingly common, there is   a greater need for some conformity in how to manage bandwidth over   such links. BACP and BAP provide a flexible yet robust way of   managing bandwidth between 2 peers.  BAP does this by defining Call-   Control packets and a protocol that allows peers to co-ordinate the   actual bandwidth allocation and de-allocation.  Phone number deltas   may be passed in the Call-Control packets to minimize the end user's   configuration.1.1.  Specification of Requirements   In this document, several words are used to signify the requirements   of the specification.  These words are often capitalized.   MUST      This word, or the adjective "required", means that the             definition is an absolute requirement of the specification.   MUST NOT  This phrase means that the definition is an absolute             prohibition of the specification.   SHOULD    This word, or the adjective "recommended", means that there             may exist valid reasons in particular circumstances to             ignore this item, but the full implications must be             understood and carefully weighed before choosing a             different course.Richards & Smith            Standards Track                     [Page 2]

RFC 2125                       PPP BACP                       March 1997   MAY       This word, or the adjective "optional", means that this             item is one of an allowed set of alternatives.  An             implementation which does not include this option MUST be             prepared to interoperate with another implementation which             does include the option.1.2.  Terminology   This document frequently uses the following terms:   peer      The other end of the point-to-point link   silently discard         This means the implementation discards the packet without         further processing.  The implementation SHOULD provide the         capability of logging the error, including the contents of the         silently discarded packet, and SHOULD record the event in a         statistics counter.   BOD (bandwidth on demand)         BOD refers to the ability of a system to allocate and remove         links in a multilink system to change the bandwidth of a         multilink bundle.  This may be done in response to changing         line conditions and it also may be done in response to changing         resource conditions.  In either case, changing bandwidth         dynamically during a multilink connection is referred to as         BOD.2.  New LCP Configuration Option   Implementations MUST implement LCP as defined in [1].  LCP MUST be in   the Network-Layer Protocol phase before BACP can be negotiated.2.1.  Link Discriminator   Description      This LCP Configuration Option is used to declare a unique      discriminator for the link that the option is sent over.  This      option MUST be negotiated by LCP on every link.  BAP uses the link      discriminator to differentiate the various links in a multilink      bundle. Each link in a multilink bundle MUST have a unique      discriminator.  The discriminator is independent for each peer, so      each link may have 2 different LCP Link Discriminator values, one      for each peer. When the Link Discriminator is sent in a BAP      packet, the transmitter sends the Link Discriminator Option value      received from its peer in the peer's LCP Configure Request packet.Richards & Smith            Standards Track                     [Page 3]

RFC 2125                       PPP BACP                       March 1997   A summary of the Link Discriminator LCP Option format is shown below.   The fields are transmitted from left to right.    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |     Length    |       Link Discriminator      |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      23 for Link Discriminator option.   Length      4   Link Discriminator      The Link Discriminator field is 2 octets in Length, and it      contains a unique identifier used to indicate a particular link in      a multilink bundle.  The Link Discriminator for a link MUST be      unique among the Link Discriminators assigned by this endpoint for      this bundle.  The Link Discriminator MAY be assigned in a      sequential, monotonically increasing manner.3.  BACP Operation   BACP uses the same packet exchange mechanism as the Link Control   Protocol defined in [1].  BACP packets MUST NOT be exchanged until   PPP has reached the Network-Layer Protocol phase.  BACP packets   received before this phase is reached should be silently discarded.   BACP is negotiated once per multilink bundle.  If BACP is negotiated   on any of the links in a multilink bundle, it is opened for all of   the links in the bundle.   The Bandwidth Allocation Control Protocol is exactly the same as the   Link Control Protocol [1] with the following exceptions:      Data Link Layer Protocol Field         Exactly one BACP packet is encapsulated in the Information         field of PPP Data Link Layer frames where the Protocol field         indicates Type hex c02b (Bandwidth Allocation Control         Protocol).Richards & Smith            Standards Track                     [Page 4]

RFC 2125                       PPP BACP                       March 1997      Code field         Only Codes 1 through 7 (Configure-Request, Configure-Ack,         Configure-Nak, Configure-Reject, Terminate-Request, Terminate-         Ack and Code-Reject) are used.  Other Codes should be treated         as unrecognized and should result in Code-Rejects.   Configuration Option Types         BACP has a distinct set of Configuration Options, which are         defined in the next section.4.  BACP Configuration Options   BACP Configuration Options allow negotiation of desirable BACP   parameters.  These options are used in Config-Request, Config-Ack,   Config-Nak, and Config-Reject packets.  BACP uses the same   Configuration Option format defined for LCP [1], with a seperate set   of Options.   Current values of BACP Configuration Options are assigned as follows:      1     Favored-Peer4.1.  Favored-Peer   Description      This Configuration Option is used to determine which peer is      favored in the event of a race condition in which 2 peers      simultaneously transmit the same BAP request.  Each peer      negotiates a 4 octet magic number, which is successfully      negotiated when the 2 Magic-Numbers are different.  The favored      peer is the peer that transmits the lowest Magic-Number in its      Favored-Peer Configuration Option.      The Favored-Peer Configuration Option MUST be implemented.Richards & Smith            Standards Track                     [Page 5]

RFC 2125                       PPP BACP                       March 1997      BACP will usually be negotiated after only one link of a multilink      bundle has reached the Network-Layer Protocol phase. In this      situation, it is acceptable for the peer that initiated the      connection to use a Magic-Number of 1, and the peer that responded      to the connection to use a Magic-Number of 0xFFFFFFFF.  If a      multilink bundle has been established with links that were      originated by each peer, or if it is not clear which peer has      initiated a link (on a leased line, for example), then a random      number MUST be used for the Magic-Number.  Refer to the      description of the LCP Magic-Number Configuration Option in [1]      for an explanation of how to create a useful random number.      When a Configure-Request is received with a Favored-Peer      Configuration Option, the received Magic-Number is compared with      the Magic-Number of the last Configure-Request sent to the peer.      If the two Magic-Numbers are different, then the Favored-Peer      negotiation has been successful, and the Favored-Peer Option      SHOULD be acknowledged.  If the two Magic-Numbers are equal, a      Configure-Nak MUST be sent specifying a different Magic-Number      value.  A new Configure-Request SHOULD NOT be sent to the peer      until normal processing would cause it to be sent (that is, until      a Configure-Nak is received or the Restart timer runs out).   A summary of the Favored-Peer Option format is shown below.  The   fields are transmitted from left to right.    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |          Magic-Number   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         Magic-Number (cont)       |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      1 for Favored-Peer   Length      6   Magic-Number      The Magic-Number field is four octets, and indicates a number      which is very likely to be unique to one end of the link.  A      Magic-Number of zero is illegal and MUST always be Nak'd.Richards & Smith            Standards Track                     [Page 6]

RFC 2125                       PPP BACP                       March 19975.  BAP Operation5.1.  Link Management   BAP defines packets, parameters and negotiation procedures to allow   two endpoints to negotiate gracefully adding and dropping links from   a multilink bundle.  An implementation can:      o Request permission to add a Link to a bundle (Call-Request)      o Request that the peer add a link to a bundle via a callback        (Callback-Request)      o Negotiate with the peer to drop a link from a bundle (this        implies that the peer can refuse) (Link-Drop-Query-Request)   After BACP reaches the opened state, either peer MAY request that   another link be added to the bundle by sending a BAP Call- or   Callback-Request packet.  A Call-Request packet is sent if the   implementation wishes to originate the call for the new link, and a   Callback-Request packet is sent if the implementation wishes its peer   to originate the call for the new link.  The implementation receiving   a Call- or Callback-Request MUST respond with a Call- or Callback-   Response with a valid Response Code.   After BACP reaches the opened state, either peer MAY request that a   link be dropped from the bundle.  A BAP Link-Drop-Query-Request   packet is sent to the peer to negotiate dropping a link.  The peer   MUST respond with a Link-Drop-Query-Response.   If the peer is   agreeable to dropping the link the implementation MUST issue an LCP   Terminate-Request to initiate dropping the link.   If an implementation wishes to force dropping a link without   negotiation, it should simply send an LCP Terminate-Request packet on   the link (without sending any BAP Link-Drop-Query-Request).   After an LCP Terminate-Request is sent an implementation SHOULD stop   transmitting data packets on that link, but still continue to receive   and process data packets normally until receipt of a Terminate-Ack   from the peer.  The receiver of an LCP Terminate-Request SHOULD stop   transmitting packets before issuing the Terminate-Ack.  This   procedure will insure that no data is lost in either direction.Richards & Smith            Standards Track                     [Page 7]

RFC 2125                       PPP BACP                       March 19975.2.  Bandwidth Management   BAP allows two peer implementations to manage the bandwidth available   to the protocols using the multilink bundle by negotiating when to   add and drop links (See Link Management).  Use of the negotiation   features of BAP makes it unnecessary to require a 'common' algorithm   for determining when to add and remove links in a multilink bundle.   BOD decisions can be based on link utilization.  A BAP implementation   may monitor its transmit traffic, both transmit and receive traffic,   or choose not to monitor traffic in either direction.  If a server   system implements bi-directional monitoring, it will allow BOD   operation with a client that does not monitor traffic in either   direction, which will minimize the end-user's configuration.  When an   implementation decides that it is time to remove a link due to   traffic monitoring, it MUST transmit a Link-Drop-Query-Request to   inquire if the peer agrees to drop a link from the current multilink   bundle.  When an implementation receives a Link-Drop-Query-Request,   it SHOULD base its response on the traffic it is monitoring.  It MUST   NOT base its response solely on its receive data heuristics.   The operation of the Link-Drop-Query-Request and -Response datagrams   causes a link in a multilink bundle to be left up as long as either   implementation that is monitoring link utilization determines that it   is necessary.   BOD decisions can also be based on the resources (e.g., physical   port, B-channel, etc.) available to an implementation.  For example,   an implementation might remove a link from a multilink bundle to   answer an incoming voice call, or might add a link when a line   becomes free due to the termination of a separate PPP call on another   port.  An implementation MUST use an LCP Terminate-Request to remove   a link due to a resource condition.5.3.  BAP Packets   All of the BAP Request and Indication packets require a Response   packet in response before taking any action.   An implementation MUST set a timer when sending a Request or   Indication packet. The value of this timer SHOULD depend on the type   and speed of the link or links in use.  Upon expiration of this   timer, the implementation MUST retransmit the request or indication,   with an identical identification number.  This procedure will insure   that the peer receives the proper request or indication even if a   packet is lost during transmission.  If a response packet is lost the   peer will realize that this is not a new request or indication   packet.Richards & Smith            Standards Track                     [Page 8]

RFC 2125                       PPP BACP                       March 1997   If the number of retransmissions exceeds the number supported by the   implementation for this packet, the implementation MAY take   appropriate recovery action. For example, if no response to a Link-   Drop-Query-Request is received after 2 retransmissions, an   implementation MAY initiate dropping the link by sending an LCP   Terminate-Request for that link.   Since BAP packets help determine the amount of bandwidth available to   an implementation, PPP SHOULD give them priority over other data   packets when transmitting.  This will help insure the prompt addition   and removal of links in a multilink bundle.  This is especially   important when adding links to a bundle due to bandwidth constraints.5.4.  Race Conditions   In order to resolve race conditions, an implementation MUST implement   the BACP Favored-Peer Configuration Option.   A race condition can occur if both implementations send a Call-   Request, Callback-Request or Link-Drop-Query-Request at the same   time.  These race conditions should be solved as follows:      If each implementation sends a Call-Request or Callback-Request at      the same time, the implementation with the lowest BACP Favored-      Peer Magic-Number value SHOULD be favored.      If each implementation sends a Link-Drop-Query-Request at the same      time, the same scheme SHOULD be used as for Call-Requests.5.5.  BAP Datagram Format   Description      Before any BAP packets may be communicated, PPP MUST reach the      Network-Layer Protocol phase, and BACP MUST reach the opened      state.      Exactly one BAP packet is encapsulated in the Information field of      PPP Data Link Layer frames where the Protocol field indicates type      hex c02d (Bandwidth Allocation Protocol).      Because ISDN Terminal Adapters sometimes are used to do multilink      with a non-multilink aware client, BAP datagrams MUST NOT be      compressed or encrypted.  Otherwise, the ISDN TA may not be able      to properly intercept BAP datagrams needed to control the      multilink connection.  This refers to compression of the whole      datagram; Address-and-Control-Field-Compression and Protocol-      Field-Compression are allowed if properly negotiated.Richards & Smith            Standards Track                     [Page 9]

RFC 2125                       PPP BACP                       March 1997      The maximum length of a BAP packet transmitted over a PPP link is      the same as the maximum length of the Information field of a PPP      data link layer frame.      Bandwidth Allocation Protocol datagrams can be catagorized as      either Request, Indication or Response packets.  Every Request and      Indication datagram has a corresponding Response packet.  Request      and Indication datagrams have a slightly different format from      Response datagrams, as the Response datagrams include a Response      Code octet.      All of the BAP datagrams MUST be supported by an implementation.      However, that does not mean an implementation must support all BAP      datagram actions.  An implementation MAY send a Request-Rej to a      Request that it does not implement.   A summary of the Bandwidth Allocation Protocol datagram Request and   Indication packet format is shown below.  The fields are transmitted   from left to right.    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |  Identifier   |            Length             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |   Data ...   +-+-+-+-+-+-+-+-+   A summary of the Bandwidth Allocation Protocol datagram Response   packet format is shown below.  The fields are transmitted from left   to right.    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |  Identifier   |            Length             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | Response Code |    Data ...   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      The Type field is one octet and identifies the type of BAP      datagram packet.  Datagram types are defined as follows.  This      field is coded in binary coded hexadecimal.Richards & Smith            Standards Track                    [Page 10]

RFC 2125                       PPP BACP                       March 1997         01       Call-Request         02       Call-Response         03       Callback-Request         04       Callback-Response         05       Link-Drop-Query-Request         06       Link-Drop-Query-Response         07       Call-Status-Indication         08       Call-Status-Response      The various types of BAP datagrams are explained in the following      sections.   Identifier      The Identifier field is one octet and is binary coded.  It aids in      matching Requests and Indications with Responses.  Call-Status-      Indication packets MUST use the same Identifier as was used by the      original Call-Request or Callback-Request that was used to      initiate the call.  All other Request or Indication packets MUST      use a unique Identifier for each new Request or Indication.  All      Response packets MUST use the same Identifier as the Identifier in      the Request or Indication packet being responded to.  When re-      transmitting a request or indication, the Identifier MUST be the      same as the Identifier used on the previous transmission of the      request or indication.   Length      The Length field is two octets and indicates the length of the      packet including the Type, Identifier, Length and Options fields.      It is binary encoded. Octets outside the range of the Length field      should be treated as Data Link Layer padding and should be ignored      on reception.   Response Code      The Response Code is only present in Response datagrams.  It is      binary coded and can have the following values:         00000000        Request-Ack         00000001        Request-Nak         00000010        Request-Rej         00000011        Request-Full-Nak      The Request-Ack Response Code is sent to indicate that the Request      or Indication command is valid and was successfully received by an      implementation. The Request-Nak Response Code is sent to indicate      that the Request command was received, but an implementation doesRichards & Smith            Standards Track                    [Page 11]

RFC 2125                       PPP BACP                       March 1997      not want the requested action performed at this time.  If a      Response containing a Request-Nak Response Code is received, the      original Request MAY be retried after an implementation determines      that sufficient time has elapsed.  The Request-Rej Response Code      is sent to indicate that the Request command received by an      implementation is not implemented (i.e., if reception of a      particular request type is not supported by the peer.) The      Request-Full-Nak Response Code is sent to indicate that the      Request command was received, but an implementation does not want      the requested action performed.  The Request-Full-Nak is used to      indicate that an implementation has reached the maximum (for a      Call- or Callback-Request) or the minimum (for a Link-Drop-Query-      Request) bandwidth configured or available for this multilink      bundle.  If a Response containing a Request-Full-Nak Response Code      is received, the original Request SHOULD NOT be retried until the      total bandwidth of the multilink bundle has changed.   Data      The Data field is variable in length, and will usually contain the      list of zero or more BAP Options that the sender desires to      transmit. The format of BAP Options is described in a later      chapter.5.5.1.  Call-Request   Before originating a call to add another link to a multilink bundle,   an implementation MUST transmit a Call-Request packet.  This will   inform the receiver of the request to add another link to the bundle   and give the receiver a chance to inform the implementation of the   phone number of a free port that can be called.   The options field MUST include the Link-Type option.  The options   field MAY include the No-Phone-Number and/or the Reason options.   Upon reception of a Call-Request, a Call-Response datagram MUST be   transmitted.5.5.2.  Call-Response   An implementation MUST transmit a Call-Response datagram in response   to a received Call-Request datagram.  If the Call-Request is   acceptable, the Call-Response MUST have a Response Code of Request-   Ack.  The Phone-Delta option MUST be included in a Call-Response   packet with a Response Code of Request-Ack unless the Call-Request   included the No-Phone-Number option. The options field MAY include   the Reason and/or Link-Type options.Richards & Smith            Standards Track                    [Page 12]

RFC 2125                       PPP BACP                       March 19975.5.3.  Callback-Request   An implementation that wants its peer to originate another link to   add to the multilink bundle MUST transmit a Callback-Request packet   to its peer.  This will inform the receiver of the request to add   another link to the bundle along with the number to be called.   The options field MUST include the Link-Type and Phone-Delta options.   The Reason option MAY also be included.   Upon reception of a Callback-Request, a Callback-Response datagram   MUST be transmitted.5.5.4.  Callback-Response   An implementation MUST transmit a Callback-Response datagram in   response to a received Callback-Request datagram.  If the Callback-   Request is acceptable, the Callback-Response MUST have a Response   Code of Request-Ack.  A Callback-Response packet MAY include the   Link-Type option.5.5.5.  Link-Drop-Query-Request   An implementation that determines that a link is no longer needed and   wishes to negotiate dropping it (e.g., based on a throughput BOD   decision), MUST transmit a Link-Drop-Query-Request packet. The   options field MUST include the Link-Discriminator option (containing   the receiver's Link-Discriminator), and MAY include the Reason   option.   Upon reception of a Link-Drop-Query-Request, an implementation MUST   transmit a Link-Drop-Query-Response datagram.  The Response-Code will   be Request-Ack if it agrees to drop the link; if it does not agree to   drop the link the Response-Code will be Request-Nak or Request-Full-   Nak.  After the receipt of a Link-Drop-Query-Response with a Response   Code of Request-Ack, the transmitter of the Link-Drop-Query-Request   MUST initiate tear down of the indicated link by sending an LCP   Terminate-Request packet on the designated link.5.5.6.  Link-Drop-Query-Response   An implementation transmits a Link-Drop-Query-Response datagram in   response to a received Link-Drop-Query-Request datagram.  If the   implementation agrees (e.g., based on its throughput BOD algorithm)   to reduce the bandwidth of the multilink bundle, then the Response   Code MUST be set to Request-Ack.Richards & Smith            Standards Track                    [Page 13]

RFC 2125                       PPP BACP                       March 1997   The Reason option MAY be included in the Link-Drop-Query-Response   packet.   The Link-Drop-Query-Request datagram MUST be supported, as well as   the underlying implementation to respond to it.  This means that a   Link-Drop-Query-Response with a Response Code of Request-Rej MUST NOT   be transmitted in response to a Link-Drop-Query-Request.5.5.7.  Call-Status-Indication   After an implementation attempts to add a link to a bundle as the   result of a Call-Request or a Callback-Request, it MUST send a Call-   Status-Indication packet to its peer to indicate if the attempt to   add the link succeeded or failed.  One Indication MUST be sent for   each attempt made. For each Call-Status-Indication packet transmitted   with the Call-Status Option Action octet set to Retry, a subsequent   Call-Status-Indication packet MUST be sent to indicate the success or   failure of the retry.  The Call-Status option MUST be included to   inform the receiver of the status of the attempt to add a link and   the action the implementation will take in case of failure.  The   reason option MAY also be included in the Call-Status-Indication   packet.   Upon reception of a Call-Status-Indication packet which indicates a   failure, an implementation may log the failure and reason code.  Upon   reception of any Call-Status-Indication packet, a Call-Status-   Response datagram MUST be transmitted.5.5.8.  Call-Status-Response   An implementation transmits a Call-Status-Response datagram in   response to a received Call-Status-Indication datagram.  The Response   Code field MUST be set to Request-Ack in this packet.  The Reason   option MAY be included in this packet.6.  BAP Datagram Options   BAP Datagram Options are used in various BAP packets.  Their use in   various packets is as defined below.  The format of these options   loosely follows the formatting conventions of LCP Configuration   Options.  When there are multiple BAP Options in one BAP packet, the   options MAY be transmitted in any order.Richards & Smith            Standards Track                    [Page 14]

RFC 2125                       PPP BACP                       March 1997   A summary of the BAP Option format is shown below.  The fields are   transmitted from left to right.    0                   1    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |    Data ...   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      The type field is one octet, and indicates the type of the BAP      Datagram Option.  This field is binary coded Hexadecimal.  The      following options are currently defined:         01   Link-Type         02   Phone-Delta         03   No-Phone-Number-Needed         04   Reason         05   Link-Discriminator         06   Call-Status   Length      The Length field is one octet, and indicates the length of this      BAP Option including the Type, Length, and Data fields.   Data      The Data field is zero or more octets, and contains information      specific to the BAP Option.  The format and length of the Data      field is determined by the Type and Length fields.6.1.  Link-Type   Description      This option indicates the general type of link indicated for the      operation being performed.  This option does not indicate a      specific link type, rather it gives some general characteristics      of the desired link type.  This option MAY be used along with      other knowledge (i.e., the type of the other link(s) in the bundle      or user configuration) to determine the type of link desired to be      used in the operation.  It MUST be included in a Call- or      Callback-Request, and MAY be included in a Call- or Callback-      Response.Richards & Smith            Standards Track                    [Page 15]

RFC 2125                       PPP BACP                       March 1997   A summary of the Link-Type BAP Option format is shown below.  The   fields are transmitted from left to right.    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |       Link Speed (kbps)       |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Link Type    |   +-+-+-+-+-+-+-+-+   Type      01 for Link-Type.   Length      The Length field is one octet, and indicates the length of this      BAP Option including the Type, Length and Link Type fields.   Link Speed      The Link Speed field is 2 octets, and indicates the requested      speed of the desired link in kilobits per second.  This field is      coded as 2 binary coded hexadecimal octets, with the most      significant octet sent first.   Link Type      The Link Type field is a bit mask.  It is 1 octet in length.  Bit      0 of the Link Type field corresponds to bit 39 of the Link-Type      BAP Option as described above.  If a bit is set, it indicates      support of the corresponding link type.  If the link indicated is      different than the supported link types, no bit will be set.      Otherwise, at least one bit MUST be set.  If an implementation      supports more than one link type, more than one bit MAY be set.         Bit     Link type         ---     -------------          0      ISDN          1      X.25          2      analog          3      switched digital (non-ISDN)          4      ISDN data over voice          5-7    reserved      If the Length field contains more bits than are defined by this      specification, then any bits that are not defined should beRichards & Smith            Standards Track                    [Page 16]

RFC 2125                       PPP BACP                       March 1997      ignored.  In order to allow for future expansion of this field, it      is important to properly support receiving a Link Type field      longer than what is defined by this specification.  If the Length      field is shorter than the number of bits defined, then the      implementation should set all bits not received to 0.6.2.  Phone-Delta   Description      The BAP Phone-Delta Option is used by an implementation to give      its peer the information needed to make a call.  Due to the      difficulty of determining which dialing prefixes (if any) are      necessary to dial a given phone number/national destination      code/country code combination, the phone number to be dialed will      be based on a previously known number.  This MAY be the original      number used to establish the first link of the multilink bundle, a      number configured by the user, the phone number used to make a      callback connection, or a number determined in some other way.      The Phone-Delta Option will consist of a Subscriber-Number Sub-      Option along with a Unique-Digits Sub-Option that indicates how      many of the digits of the Subscriber-Number are unique among the      ports in use, previously used, and to be used in the multilink      bundle.  There is also an optional Phone-Number-Sub-Address Sub-      Option.      An implementation MAY include more than one Phone-Delta option in      a response.  This indicates that there is more than one phone      number that can be used for the requested operation.  The Phone-      Delta option MUST appear in a Callback-Request.  It also MUST      appear in a Call-Response with a Response Code set to Request-Ack      if the Call-Request did not contain the No-Phone-Number option.      It MAY be included in the Call-Status-Indication packet.   A summary of the Phone-Delta BAP Option format is shown below.  The   fields are transmitted from left to right.    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |Sub-Option Type| Sub-Option Len|   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Sub-Option...   +-+-+-+-+-+-+-+-+   Type      02 for Phone-Delta.Richards & Smith            Standards Track                    [Page 17]

RFC 2125                       PPP BACP                       March 1997   Length      The Length field is one octet, and indicates the length of this      BAP Option including the Type, Length, and Sub-Option fields.   Sub-Option Type      The following Sub-Option Types are defined for the Phone-Delta      option.          01   Unique-Digits          02   Subscriber-Number          03   Phone-Number-Sub-Address   Sub-Option Length      The Sub-Option Length field is one octet, and indicates the length      of this BAP Sub-Option including the Sub-Option Type, Sub-Option      Length, and Sub-Option fields.6.2.1.  Phone-Delta Sub-Options   Unique-Digits      The Unique-Digits Sub-Option field consists of one octet that is a      count of the number of rightmost digits of the Subscriber-Number      that are different from the set of phone numbers of the ports used      in this multilink connection.  (For example, if the first port of      a multilink bundle has a phone number of 123456789, and an      implementation wanted its peer to call a port with a phone number      of 123456888, the Unique-Digits octet would be 3.) If the Phone-      Number-Sub-Address Sub-Option is present, the Unique-Digits Sub-      Option MUST NOT include any of the Sub Address digits in its count      of different rightmost digits.      This field is required.   Subscriber-Number      This field is the phone number of the port that should be called      by the peer. Any digits that precede the rightmost unique digits      of the Subscriber-Number are provided for informational purposes      only, and do not need to be included in this field.  This field is      an ASCII string and MUST contain only ASCII characters indicating      valid phone number digits.  This field is required.Richards & Smith            Standards Track                    [Page 18]

RFC 2125                       PPP BACP                       March 1997   Phone-Number-Sub-Address      This field is the sub address of the port to be called by the      peer.  This sub-option SHOULD only be used for an ISDN call. This      field is an ASCII string and only contains valid phone number      digits. This field is optional.6.3.  No-Phone-Number-Needed   Description      The No-Phone-Number option indicates that the calling      implementation is already configured with the phone number of its      multilink peer and the answering implementation MUST NOT include      the Phone Number option in the response.  This may be for security      reasons, for configuration reasons, or for any other reason.      This option MAY be used in a Call-Request packet.   A summary of the No-Phone-Number BAP Option format is shown below.   The fields are transmitted from left to right.    0                   1    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      03 for No-Phone-Number.   Length      2Richards & Smith            Standards Track                    [Page 19]

RFC 2125                       PPP BACP                       March 19976.4.  Reason   Description      This option is used to indicate a reason for the Request or      Response.  It is meant to be used for informational purposes only.      This option MAY be used in any BAP packet.   A summary of the Reason BAP Option format is shown below.  The fields   are transmitted from left to right.    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |         Reason String...   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      04 for Reason.   Length      The Length field is one octet, and indicates the length of this      BAP Option including the Type, Length and Reason String fields.   Reason String      This is an ASCII string.  The content of the field is      implementation dependent.  An implementation MAY ignore the Reason      String field.Richards & Smith            Standards Track                    [Page 20]

RFC 2125                       PPP BACP                       March 19976.5.  Link-Discriminator   Description      The Link-Discriminator option MUST be used in a Link-Drop-Query-      Request datagram.  This option is used to inform the receiver of a      Link-Drop-Query-Request of which link will be dropped.   A summary of the Link-Discriminator BAP Option format is shown below.   The fields are transmitted from left to right.    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |       Link Discriminator      |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      05 for Link-Discriminator   Length      4   Link Discriminator      The Link Discriminator field is 2 octets in length.  It contains      the Link Discriminator that was contained in the LCP Link-      Discriminator Configuration Option sent by the receiver of the      packet containing the Link Discriminator.6.6.  Call-Status   Description      The Call-Status option MUST be used in a Call-Status-Indication      datagram.  This option is used to inform the receiver of the      Call-Status-Indication datagram of the status of the completed      call attempt, as well as a possible action that will be taken (if      the call failed).Richards & Smith            Standards Track                    [Page 21]

RFC 2125                       PPP BACP                       March 1997   A summary of the Call-Status BAP Option format is shown below.  The   fields are transmitted from left to right.    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |     Status    |     Action    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      06 for Call-Status.   Length      4   Status      The Status field is 1 octet in length.  If the call was      successful, the value MUST be set to 0.  A non-zero value      indicates a call failure.  A value of 255 indicates a non-specific      failure, and a more specific call status MAY be indicated by using      the same number as the Q.931 cause value (i.e., 1 is unassigned      number, 17 is user busy, etc.)   Action   The Action octet indicates what action the calling implementation is   taking after a failed call.  If the call was sucessful, the Action   octet MUST be set to 0.   The Action octet can have the following values:      0 - No retry      1 - RetryRichards & Smith            Standards Track                    [Page 22]

RFC 2125                       PPP BACP                       March 1997AppendixList of BAP datagrams and associated fields.datagram                      mandatory fields           allowed options--------                      -----------------          ---------------Call-Request                  Link-Type                  No-Phone-NumberCall-Response                                            Phone-Delta                                                         Link-TypeCallback-Request              Link-Type                              Phone-DeltaCallback-Response                                        Link-TypeLink-Drop-Query-Request       Link-DiscriminatorLink-Drop-Query-ResponseCall-Status-Indication        Call-Status                Phone-DeltaCall-Status-Response   The Reason option is allowed to be included with any BAP datagram.History of BACP   The first version of BACP was written by Craig Richards of Shiva   Corporation.  This version was enhanced and improved by the MPCP   Working Group, a collaborative effort of 3Com, Ascend, Bay Networks,   Cisco, Microsoft, Shiva, US Robotics and Xylogics.Acknowledgements   Kevin Smith of Ascend for his contributions based on his work on the   MP+ Specification.  Gerry Meyer and Robert Myhill of Shiva for their   early comments and improvements.  Andy Nicholson of Microsoft for his   improvements to the bandwidth management scheme.  Dana Blair and Andy   Valencia of Cisco, Cheng Chen and Dan Brennan of 3Com for their good   ideas as part of the MPCP Working Group. All of the members of the   MPCP working group for their ability to work with their competitors   with enthusiasm to produce a better protocol for the industry.Security Considerations   Security issues are not discussed in this memo.Richards & Smith            Standards Track                    [Page 23]

RFC 2125                       PPP BACP                       March 1997References[1]   Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD      51,RFC 1661, Daydreamer, July 1994.[2]   Sklower, Lloyd, McGregor, Carr & Coradetti, "The PPP Multilink      Protocol",RFC 1990,  University of California, Berkeley, Lloyd      Internetworking, Newbridge Networks Corporation, Sidewalk      Software, August 1996.Chair's Address   The working group can be contacted via the current chair:      Karl Fox      Ascend Communications      3518 Riverside Drive, Suite 101      Columbus, Ohio  43221      (614)451-1883      EMail: karl@ascend.comEditors' Addresses      Craig Richards      Shiva Corporation      28 Crosby Drive      Bedford, MA  01730      VOICE   +1 617 270 8419      FAX     +1 617 270 8599      EMail: crich@us.shiva.com      Kevin Smith      Ascend Communications, Inc.      1275 Harbor Bay Parkway      Alameda, CA  94501      CA      EMail: kevin@ascend.comRichards & Smith            Standards Track                    [Page 24]