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Network Working Group                                        Y. KatsubeRequest for Comments: 2098                                    K. NagamiCategory: Informational                                        H. Esaki                                                     Toshiba R&D Center                                                          February 1997Toshiba's Router Architecture Extensions for ATM : OverviewStatus of this Memo   This memo provides information for the Internet community.  This memo   does not specify an Internet standard of any kind.  Distribution of   this memo is unlimited.Abstract   This memo describes a new internetworking architecture which makes   better use of the property of ATM.  IP datagrams are transferred   along hop-by-hop path via routers, but datagram assembly/disassembly   and IP header processing are not necessarily carried out at   individual routers in the proposed architecture.  A concept of "Cell   Switch Router (CSR)" is introduced as a new internetworking   equipment, which has ATM cell switching capabilities in addition to   conventional IP datagram forwarding.  Proposed architecture can   provide applications with high-throughput and low-latency ATM pipes   while retaining current router-based internetworking concept.  It   also provides applications with specific QoS/bandwidth by cooperating   with internetworking level resource reservation protocols such as   RSVP.1.  Introduction   The Internet is growing both in its size and its traffic volume. In   addition, recent applications often require guaranteed bandwidth and   QoS rather than best effort.  Such changes make the current hop-by-   hop datagram forwarding paradigm inadequate, then accelerate   investigations on new internetworking architectures.   Roughly two distinct approaches can be seen as possible solutions;   the use of ATM to convey IP datagrams, and the revision of IP to   support flow concept and resource reservation.  Integration or   interworking of these approaches will be necessary to provide end   hosts with high throughput and QoS guaranteed internetworking   services over any datalink platforms as well as ATM.   New internetworking architecture proposed in this draft is based on   "Cell Switch Router (CSR)" which has the following properties.Katsube, et. al.             Informational                      [Page 1]

RFC 2098          Toshiba's Router Extension for ATM       February 1997    - It makes the best use of ATM's property while retaining current      router-based internetworking and routing architecture.    - It takes into account interoperability with future IP that      supports flow concept and resource reservations.Section 2 of this draft explains background and motivations of our   proposal.Section 3 describes an overview of the proposed   internetworking architecture and its several remarkable features.Section 4 discusses control architectures for CSR, which will need to   be further investigated.2.  Background and Motivation   It is considered that the current hop-by-hop best effort datagram   forwarding paradigm will not be adequate to support future large   scale Internet which accommodates huge amount of traffic with certain   QoS requirements.  Two major schools of investigations can be seen in   IETF whose main purpose is to improve ability of the Internet with   regard to its throughput and QoS.  One is to utilize ATM technology   as much as possible, and the other is to introduce the concept of   resource reservation and flow into IP.1) Utilization of ATM   Although basic properties of ATM; necessity of connection setup,   necessity of traffic contract, etc.; is not necessarily suited to   conventional IP datagram transmission, its excellent throughput and   delay characteristics let us to investigate the realization of IP   datagram transmission over ATM.   A typical internetworking architecture is the "Classical IP Model"   [RFC1577].  This model allows direct ATM connectivities only between   nodes that share the same IP address prefix.  IP datagrams should   traverse routers whenever they go beyond IP subnet boundaries even   though their source and destination are accommodated in the same ATM   cloud.  Although an ATMARP is introduced which is not based on legacy   datalink broadcast but on centralized ATMARP servers, this model does   not require drastic changes to the legacy internetworking   architectures with regard to the IP datagram forwarding process.   This model still has problems of limited throughput and large   latency, compared with the ability of ATM, due to IP header   processing at every router.  It will become more critical when   multimedia applications that require much larger bandwidth and lower   latency become dominant in the near future.Katsube, et. al.             Informational                      [Page 2]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   Another internetworking architecture is "NHRP (Next Hop Resolution   Protocol) Model" [NHRP09].  This model aims at resolving throughput   and latency problems in the Classical IP Model and making the best   use of ATM.  ATM connections can be directly established from an   ingress point to an egress point of an ATM cloud even when they do   not share the same IP address prefix.  In order to enable it, the   Next Hop Server [KAT95] is introduced which can find an egress point   of the ATM cloud nearest to the given destination and resolves its   ATM address.  A sort of query/response protocols between the   server(s) and clients and possibly server and server are specified.   After the ATM address of a desired egress point is resolved, the   client establishes a direct ATM connection to that point through ATM   signaling procedures [ATM3.1].  Once a direct ATM connection has been   set up through this procedure, IP datagrams do not have to experience   hop-by-hop IP processing but can be transmitted over the direct ATM   connection.  Therefore, high throughput and low latency   communications become possible even if they go beyond IP subnet   boundaries.  It should be noted that the provision of such direct ATM   connections does not mean disappearance of legacy routers which   interconnect distinct ATM-based IP subnets.  For example, hop-by-hop   IP datagram forwarding function would still be required in the   following cases:   - When you want to transmit IP datagrams before direct ATM connection     from an ingress point to an egress point of the ATM cloud is     established   - When you neither require a certain QoS nor transmit large amount of     IP datagrams for some communication   - When the direct ATM connection is not allowed by security or policy     reasons2) IP level resource reservation and flow support   Apart from investigation on specific datalink technology such as ATM,   resource reservation technologies for desired IP level flows have   been studied and are still under discussion.  Their typical examples   are RSVP [RSVP13] and STII [RFC1819].   RSVP itself is not a connection oriented technology since datagrams   can be transmitted regardless of the result of the resource   reservation process.  After a resource reservation process from a   receiver (or receivers) to a sender (or senders) is successfully   completed, RSVP-capable routers along the path of the flow reserve   their resources for datagram forwarding according to the requested   flow spec.Katsube, et. al.             Informational                      [Page 3]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   STII is regarded as a connection oriented IP which requires   connection setup process from a sender to a receiver (or receivers)   before transmitting datagrams.  STII-capable routers along the path   of the requested connection reserve their resources for datagram   forwarding according to the flow spec.   Neither RSVP nor STII restrict underlying datalink networks since   their primary purpose is to let routers provide each IP flow with   desired forwarding quality (by controlling their datagram scheduling   rules).  Since various datalink networks will coexist as well as ATM   in the future, these IP level resource reservation technologies would   be necessary in order to provide end-to-end IP flow with desired   bandwidth and QoS.   aking this background into consideration, we should be aware of   several issues which motivate our proposal.   - As of the time of writing, the ATM specific internetworking     architecture proposed does not take into account interoperability     with IP level resource reservation or connection setup protocols.     In particular, operating RSVP in the NHRP-based ATM cloud seems to     require much effort since RSVP is a soft-state receiver-oriented     protocol with multicast capability as a default, while ATM with     NHRP is a hard-state sender-oriented protocol which does not     support multicast yet.   - Although RSVP or STII-based routers will provide each IP flow with     a desired bandwidth and QoS, they have some native throughput     limitations due to the processor-based IP forwarding mechanism     compared with the hardware switching mechanism of ATM.   The main objective of our proposal is to resolve the above issues.   The proposed internetworking architecture makes the best use of the   property of ATM by extending legacy routers to handle future IP   features such as flow support and resource reservation with the help   of ATM's cell switching capabilities.3.  Internetworking Architecture Based On the Cell Switch Router (CSR)3.1  Overview   The Cell Switch Router (CSR) is a key network element of the proposed   internetworking architecture.  The CSR provides cell switching   functionality in addition to conventional IP datagram forwarding.   Communications with high throughput and low latency, that are native   properties of ATM, become possible by using this cell switching   functionality even when the communications pass through IP subnetworkKatsube, et. al.             Informational                      [Page 4]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   boundaries.  In an ATM internet composed of CSRs, VPI/VCI-based cell   switching which bypasses datagram assembly/disassembly and IP header   processing is possible at every CSR for communications which lend   themselves to such (e.g., communications which require certain amount   of bandwidth and QoS), while conventional hop-by-hop datagram   forwarding based on the IP header is also possible at every CSR for   other conventional communications.   By using such cell-level switching capabilities, the CSR is able to   concatenate incoming and outgoing ATM VCs, although the concatenation   in this case is controlled outside the ATM cloud (ATM's control/   management-plane) unlike conventional ATM switch nodes.  That is, the   CSR is attached to ATM networks via an ATM-UNI instead of NNI.  By   carrying out such VPI/VCI concatenations at multiple CSRs   consecutively, ATM level connectivity composed of multiple ATM VCs,   each of which connects adjacent CSRs (or CSR and hosts/routers), can   be provided.  We call such an ATM pipe "ATM Bypass-pipe" to   differentiate it from "ATM VCC (VC connection)" provided by a single   ATM datalink cloud through ATM signaling.   Example network configurations based on CSRs are shown in figure 1.   An ATM datalink network may be a large cloud which accommodates   multiple IP subnets X, Y and Z.  Or several distinct ATM datalinks   may accommodate single IP subnet X, Y and Z respectively.  The latter   configuration would be straightforward in discussing the CSR, but the   CSR is also applicable to the former configuration as well.  In   addition, the CSR would be applicable as a router which interconnects   multiple NHRP-based ATM clouds.   Two different kinds of ATM VCs are defined between adjacent CSRs or   between CSR and ATM-attached hosts/routers.1) Default-VC   It is a general purpose VC used by any communications which select   conventional hop-by-hop IP routed paths.  All incoming cells received   from this VC are assembled to IP datagrams and handled based on their   IP headers.  VCs set up in the Classical IP Model are classified into   this category.2) Dedicated-VC   It is used by specific communications (IP flows) which are specified   by, for example, any combination of the destination IP address/port,   the source IP address/port or IPv6 flow label.  It can be   concatenated with other Dedicated-VCs which accommodate the same IP   flow as it, and can constitute an ATM Bypass-pipe for those IP flows.Katsube, et. al.             Informational                      [Page 5]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   Ingress/egress nodes of the Bypass-pipe can be either CSRs or ATM-   attached routers/hosts both of which speak a Bypass-pipe control   protocol.  (we call that "Bypass-capable nodes") On the other hand,   intermediate nodes of the Bypass-pipe should be CSRs since they need   to have cell switching capabilities as well as to speak the Bypass-   pipe control protocol.   The route for a Bypass-pipe follows IP routing information in each   CSR.  In figure 1, IP datagrams from a source host or router X.1 to a   destination host or router Z.1 are transferred over the route X.1 ->   CSR1 -> CSR2 -> Z.1 regardless of whether the communication is on a   hop-by-hop basis or Bypass-pipe basis.  Routes for individual   Dedicated-VCs which constitutes the Bypass-pipe X.1 --> Z.1 (X.1 ->   CSR1, CSR1 -> CSR2, CSR2 -> Z.1) would be determined based on ATM   routing protocols such as PNNI [PNNI1.0], and would be independent of   IP level routing.   An example of IP datagram transmission mechanism is as follows.   o The host/router X.1 checks an identifier of each IP datagram,     which may be the "destination IP address (prefix)",     "source/destination IP address (prefix) pair", "destination IP     address and port", "source IP address and Flow label (in IPv6)",     and so on.  Based on either of those identifiers, it determines     over which VC the datagram should be transmitted.   o The CSR1/2 checks the VPI/VCI value of each incoming cell.  When     the mapping from the incoming interface/VPI/VCI to outgoing     interface/VPI/VCI is found in an ATM routing table, it is directly     forwarded to the specified interface through an ATM switch module.     When the mapping in not found in the ATM routing table (or the     table shows an IP module as an output interface), the cell is     assembled to an IP datagram and then forwarded to an appropriate     outgoing interface/VPI/VCI based on an identifier of the datagram.Katsube, et. al.             Informational                      [Page 6]

RFC 2098          Toshiba's Router Extension for ATM       February 1997        IP subnet X           IP subnet Y          IP subnet Z  <---------------------> <-----------------> <--------------------->  +-------+ Default  +-------+ Default   +-------+ Default  +-------+  |       |     -VC  | CSR 1 |     -VC   | CSR 2 |     -VC  |       |  | Host +=============+   +===============+   +=============+ Host |  |  X.1 +-------------+++++---------------+++++-------------+  Z.1 |  |      +-------------+++++---------------+++++-------------+      |  |      +-------------+++++---------------+++++-------------+      |  |       |Dedicated |       | Dedicated |       |Dedicated |       |  +-------+     -VCs +-------+      -VCs +-------+     -VCs +-------+         <--------------------------------------------------->                             Bypass-pipe         Figure 1  Internetworking Architecture based on CSR3.2  Features   The main feature of the CSR-based internetworking architecture is the   same as that of the NHRP-based architecture in the sense that they   both provide direct ATM level connectivity beyond IP subnet   boundaries.  There are, however, several notable differences in the   CSR-based architecture compared with the NHRP-based one as follows.1) Relationship between IP routing and ATM routing   In the NHRP model, an egress point of the ATM network is first   determined in the next hop resolution phase based on IP level routing   information.  Then the actual route for an ATM-VC to the obtained   egress point is determined in the ATM connection setup phase based on   ATM level routing information.  Both kinds of routing information   would be calculated according to factors such as network topology and   available bandwidth for the large ATM cloud.  The ATM routing will be   based on PNNI phase1 [PNNI1.0] while the IP routing will be based on   OSPF, BGP, IS-IS, etc.  We need to manage two different routing   protocols over the large ATM cloud until Integtrated-PNNI [IPNNI96]   which takes both ATM level metric and IP level metric into account   will be phased in in the future.   In the CSR model, IP level routing determines an egress point of the   ATM cloud as well as determines inter-subnet level path to the point   that shows which CSRs it should pass through.  ATM level routing   determines an intra-subnet level path for ATM-VCs (both Dedicated-VC   and Default-VC) only between adjacent nodes (CSRs or ATM-attached   hosts/routers).  Since the roles of routing are hierarchically   subdivided into inter-subnet level (router level) and intra-subnet   level (ATM SW level), ATM routing does not have to operate all overKatsube, et. al.             Informational                      [Page 7]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   the ATM cloud but only in individual IP subnets independent from each   other.  This will decrease the amount of information for ATM routing   protocol handling.  But an end-to-end ATM path may not be optimal   compared with the NHRP model since the path should go through routers   at subnet boundaries in the CSR model.2) Dynamic routing and redundancy support   A CSR-based network can dynamically change routes for Bypass-pipes   when related IP level routing information changes.  Bypass-pipes   related to the routing changes do not have to be torn down nor   established from scratch since intermediate CSRs related to IP   routing changes can follow them and change routes for related   Bypass-pipes by themselves.   The same things apply when some error or outage happens in any ATM   nodes/links/routers on the route of a Bypass-pipe.  CSRs that have   noticed such errors or outages would change routes for related   Bypass-pipes by themselves.3) Interoperability with IP level resource reservation protocols in   multicast environments   As current NHRP specification assumes application of NHRP to unicast   environments only, multicast IP flows should still be carried based   on a hop-by-hop manner with multicast routers.  In addition,   realization of IP level resource reservation protocols such as RSVP   over NHRP environments requires further investigation.   The CSR-based internetworking architecture which keeps subnet-by-   subnet internetworking with regard to any control protocol sequence   can provide multicast Bypass-pipes without requiring any   modifications in IP multicast over ATM [IPMC96] or multicast routing   techniques.  In addition, since the CSR can handle RSVP messages   which are transmitted in a hop-by-hop manner, it can provide Bypass-   pipes which satisfy QoS requirements by the cooperation of the RSVP   and the Bypass-pipe control protocol.4.  Control Architecture for CSR   Several issues with regard to a control architecture for the CSR are   discussed in this section.4.1  Network Reference Model   In order to help understanding discussions in this section, the   following network reference model is assumed.  Source hosts S1, S2,   and destination hosts D1, D2 are attached to Ethernets, while S3 andKatsube, et. al.             Informational                      [Page 8]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   D3 are attached to the ATM.  Routers R1 and R5 are attached to   Ethernets only, while R2, R3 and R4 are attached to the ATM.  The ATM   datalink for subnet #3 and subnet #4 can either be physically   separated datalinks or be the same datalink.  In other words, R3 can   be either one-port or multi-port router.      Ether    Ether        ATM          ATM        Ether    Ether        |        |        +-----+      +-----+        |        |        |        |        |     |      |     |        |        |    S1--|   S2---|   S3---|     |      |     |---D3   |---D2   |--D1        |        |        |     |      |     |        |        |        |---R1---|---R2---|     |--R3--|     |---R4---|---R5---|        |        |        |     |      |     |        |        |        |        |        +-----+      +-----+        |        |     subnet   subnet      subnet       subnet      subnet   subnet       #1       #2          #3           #4          #5       #6                   Figure 2  Network Reference Model   Bypass-pipes can be configured [S3 or R2]-->R3-->[D3 or R4].  That   means that S3, D3, R2, R3 and R4 need to speak Bypass-pipe control   protocol, and means that R3 needs to be the CSR.  We use term   "Bypass-capable nodes" for hosts/routers which can speak Bypass-pipe   control protocol but are not necessarily CSRs.   As shown in this reference model, Bypass-pipe can be configured from   host to host (S3-->R3-->D3), router to host (R2-->R3-->D3), host to   router (S3-->R3-->R4), and router to router (R2-->R3-->R4).4.2  Possible Use of Bypass-pipe   Possible use (or purposes) of Bypass-pipe provided by CSRs, in other   words, possible triggers that initiate Bypass-pipe setup procedure,   is discussed in this subsection.   Following two purposes for Bypass-pipe setup are assumed at present;a) Provision of low latency path   This indicates cases in which end hosts or routers initiate a   Bypass-pipe setup procedure when they will transmit large amount of   datagrams toward a specific destination.  For instance,   - End hosts or routers initiate Bypass-pipe setup procedures based     on the measurement of IP datagrams transmitted toward a certain     destination.Katsube, et. al.             Informational                      [Page 9]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   - End hosts or routers initiate Bypass-pipe setup procedures when     it detects datagrams with certain higher layer protocols such as     ftp, nntp, http, etc.   Other triggers may be possible depending on the policy in each   network.  In any case, the purpose of Bypass-pipe setup in each of   these cases is to reduce IP processing burden at intermediate routers   as well as to provide a communication path with low latency for burst   data transfer, rather than to provide end host applications with   specific bandwidth/QoS.   There would be no rule for determining bandwidth for such kinds of   Bypass-pipes since no explicit information about bandwidth/QoS   requirement by end hosts is available without IP-level resource   reservation protocols such as RSVP.  Using UBR VCs as components of   the Bypass-pipe would be the easiest choice although there is no   guarantees for cell loss quality, while using other services such as   CBR/VBR/ABR with an adequate parameter tuning would be possible.b) Provision of specific bandwidth/QoS requested by hosts   This indicates cases in which routers or end hosts initiate a   Bypass-pipe setup procedure by triggers related to IP-level   bandwidth/QoS request from end hosts.  The "resource management   entity" in the host or router, which has received bandwidth/QoS   requests from applications or adjacent nodes may choose to   accommodate the requested IP flow to an existing VC or choose to   allocate a new Dedicated-VC for the requested IP flow.  Selecting the   latter choice at each router can correspond to the trigger for   constituting a Bypass-pipe.  When both an incoming VC and an outgoing   VC (or VCs) are dedicated to the same IP flow(s), those VCs can be   concatenated at the CSR (ATM cut-through) to constitute a Bypass-   pipe.  Bandwidth for the Bypass-pipe (namely, individual VCs   constituting the Bypass-pipe) in this case would be determined based   on the bandwidth/QoS requirements by the end host which is conveyed   by, e.g., RSVP messages.  The ATM service classes; e.g., CBR/VBR/ABR;   that would be selected depends on the IP-level service classes   requested by the end hosts.   Bypass-pipe provision for the purpose of b) will surely be beneficial   in the near future when related IP-level resource reservation   protocol will become available as well as when definitions of   individual service classes and flow specs offered to applications   become clear.  On the other hand, Bypass-pipe setup for the purpose   of a) may be beneficial right now since it does not require   availability of IP-level resource reservation protocols.  In that   sense, a) can be regarded as a kind of short-term use while b) is a   long-term use.Katsube, et. al.             Informational                     [Page 10]

RFC 2098          Toshiba's Router Extension for ATM       February 19974.3  Variations of Bypass-pipe Control Architecture   A number of variations regarding Bypass-pipe control architecture are   introduced.  Items which are related to architectural variations are;    o Ways of providing Dedicated-VCs    o Channels for Bypass-pipe control message transfer    o Bypass-pipe control procedures   Each of these items are discussed below.4.3.1  Ways of Providing Dedicated-VCs   There are roughly three alternatives regarding the way of providing   Dedicated-VCs in individual IP subnets as components of a Bypass-   pipe.a) On-demand SVC setup   Dedicated-VCs are set up in individual IP subnets each time you want   to set up a Bypass-pipe through the ATM signaling procedure.b) Picking up one from a bunch of (semi-)PVCs   Several VCs are set up beforehand between CSR and CSR, or CSR and   other ATM-attached nodes (hosts/router) in each IP subnet. Unused VC   is picked up as a Dedicated-VC from these PVCs in each IP subnet when   a Bypass-pipe is set up.c) Picking up one VCI in PVP/SVP   PVPs or SVPs are set up between CSR and CSR, or CSR and other ATM-   attached nodes (hosts/routers) in each IP subnet.  PVPs would be set   up as a router/host initialization procedure, while SVPs, on the   other hand, would be set up through ATM signaling when the first VC   (either Default- or Dedicated-) setup request is initiated by either   of some peer nodes.  Then, Unused VCI value is picked up as a   Dedicated-VC in the PVP/SVP in each IP subnet when a Bypass-pipe is   set up.  The SVP can be released through ATM signaling when no VCI   value is in active state.   The best choice will be a) with regard to efficient network resource   usage.  However, you may go through three steps, ATMARP (for unicast   [RFC1577] or multicast [IPMC96] in each IP subnet), SVC setup (in   each IP subnet) and exchange of Bypass-pipe control message in this   case.  Whether a) is practical choice or not will depend on whetherKatsube, et. al.             Informational                     [Page 11]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   you can allow larger Bypass-pipe setup time due to three-step   procedure mentioned above, or whether you can send datagrams over   Default-VCs in a hop-by-hop manner while waiting for the Bypass-pipe   set up.   In the case of b) or c), the issue of Bypass-pipe setup time will be   improved since SVC setup step can be skipped.  In b), each node (CSR   or ATM-attached host/router) should specify some traffic descriptors   even for unused VCs, and the ATM datalink should reserve its desired   resource (such as VCI value and bandwidth) for them.  In addition,   the ATM datalink may have to carry out UPC functions for those unused   VCs.  Such burden would be reduced when you use UBR-PVCs and set peak   cell rate for each of them equal to link rate, but bandwidth/QoS for   the Bypass-pipe is not provided in this case.  In c), on the other   hand, traffic descriptors which should be specified by each node for   the ATM datalink is not each VC's but VP's only.  Resource   reservations for individual VCs will be carried out not as a   functionality of the ATM datalink but of each CSR or ATM-attached   host/router if necessary.  A functionality which need to be provided   by the ATM datalink is control of VPs' bandwidth only such as UPC and   dynamic bandwidth negotiation if it would be widely available.4.3.2  Channels for Bypass-pipe Control Message Transfer   There are several alternatives regarding the channels for managing   (setting up, releasing, and possibly changing the route of) a   Bypass-pipe.  This subsection explains these alternatives and   discusses their properties.   Three alternatives are discussed, Inband control message, Outband   control message, and use of ATM signaling.i) Inband Control Message   When setting up a Bypass-pipe, control messages are transmitted over   a Dedicated-VC which will eventually be used as a component of the   Bypass-pipe.  These messages are handled at each CSR, and similar   messages are transmitted to the next-hop node over a Dedicated-VC   along the selected route (based on IP routing table).  Unlike outband   message protocol described in ii), each message does not have to   indicate a Dedicated-VC which will be used since the message itself   is carried over "that" VC.   The inband control message can be either "datagram dedicated for   Bypass-pipe control" or "actual IP datagram" sent by user   application.  Actual IP datagrams can be transmitted over Bypass-pipe   after it has been set up in the former case.  In the latter case, on   the other hand, the first (or several) IP datagram(s) received fromKatsube, et. al.             Informational                     [Page 12]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   an unused Dedicated-VC are analyzed at IP level and transmitted   toward adequate next hop over an unused Dedicated-VC.  Then incoming   Dedicated-VC and outgoing Dedicated-VC are concatenated to construct   a Bypass-pipe.   In inband control, Bypass-pipe control messages transmitted after a   Bypass-pipe has been set up cannot be identified at intermediate CSRs   since those messages are forwarded at cell level there.  As a   possible solution for this issue, intermediate CSRs can identify   Bypass-pipe control messages by marking cell headers, e.g., PTI bit   which indicates F5 OAM cell.  With regard to Bypass-pipe release,   explicit release message may not be necessary if individual CSRs   administer the amount of traffic over each Dedicated-VC and deletes   concatenation information for an inactive Bypass-pipe with their own   decision.ii) Outband Control Message   When a Bypass-pipe is set up or released, control messages are   transmitted over VCs which are different from Dedicated-VCs used as   components of the Bypass-pipe.  Unlike inband message protocol   described in i), each message has to indicate which Dedicated-VCs the   message would like to control.  Therefore, an identifier that   uniquely discriminates a VC, which is not a VPI/VCI that is not   identical at both endpoints of the VC, need to be defined and be   given at VC initiation phase.  However, an issue of control message   transmission after a Bypass-pipe has been set up in inband case does   not exist.   Four alternatives are possible regarding how to convey Bypass-pipe   control messages hop-by-hop over ATM datalink networks.   1) Defines VC for Bypass-pipe control messages only.   2) Uses Default-VC and discriminates Bypass-pipe control messages      from user datagrams by an LLC/SANP value inRFC1483 encapsulation.   3) Uses Default-VC and discriminates Bypass-pipe control messages      from user datagrams by a protocol field value in IP header.   4) Uses Default-VC and discriminates Bypass-pipe control messages      from user datagrams by a port ID in the UDP frame.   When we take into account interoperability with Bypass-incapable   routers, 1) will not be a good choice.  Whether we select 2) or 3) 4)   depends on whether we should consider multiprotocol rather than IP   only.Katsube, et. al.             Informational                     [Page 13]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   In the case of IP multicast, point-to-multipoint VCs in individual   subnets are concatenated at CSRs consecutively in order to constitute   end-to-end multicast tree.  Above four alternatives may require the   same number of point-to-multipoint Defalut-VCs as the number of   requested point-to-multipoint Dedicated-VCs in multicast case.  The   fifth alternative which can reduce the necessary number of VCs to   convey control messages in a multicast environment is;   5) Defines point-to-multipoint VC whose leaves are members of      multicast group 224.0.0.1.  All nodes which are members of at      least one of active multicast group would become leaves of this      point-to-multipoint VC.   Each upstream node may become a root of the point-to-multipoint VC,   or a sort of multicast server to which each upstream node transmits   cells over a point-to-point VC may become a root of that.  In any   case, Bypass-pipe control messages for every multicast group are   transmitted to all nodes which are members of either of the group.   When a downstream node has received control messages which are not   related to a multicast group it belongs, it should discard them by   referring to a destination group address on their IP header.   Donwstream node would still need to use point-to-point VC to send   control messages toward upstream.iii)  Use of ATM Signaling Message   Supposing that ATM signaling messages can convey IP addresses (and   possibly port IDs) of source and destination, it may be possible that   ATM signaling messages be used as Bypass-pipe control messages also.   In that case, an ATM connection setup message indicates a setup of a   Dedicated-VC to an ATM address of a desirable next-hop IP node, and   also indicates a setup of a Bypass-pipe to an IP address (and   possibly port ID) of a target destination node.  Information elements   for the Dedicated-VC setup (ATM address of a next-hop node,   bandwidth, QoS, etc.) are handled at ATM nodes, while information   elements for the Bypass-pipe setup (source and destination IP   addresses, possibly their port IDs, or flow label for IPv6, etc.) are   transparently transferred to the next-hop IP node.  The next-hop IP   node accepts Dedicated-VC setup and handles such IP level information   elements.   ATM signaling messages can be transferred from receiver to sender as   well as sender to receiver when you set zero Forward Cell Rate and   non-zero Backward Cell Rate as an ATM traffic descriptor information   element in unicast case, or when Leaf Initiated Join capabilities   will become available in multicast case.Katsube, et. al.             Informational                     [Page 14]

RFC 2098          Toshiba's Router Extension for ATM       February 1997   Issues in this method are,    - Information elements which specify IP level (and port level)      information need to be defined, e.g., B-HLI or B-UUI, as an ATM      signaling specification.    - It would be difficult to support soft-state Bypass-pipe control      which transmits control messages periodically since ATM signaling      is a hard-state protocol.4.3.3  Bypass-pipe Control Procedures   This subsection discusses several items with regard to actual   procedures for Bypass-pipe control.a) Distributed trigger vs. Centralized (restricted) trigger   The first item to be discussed is whether the functionality of   detecting a trigger of Dedicated-VC/Bypass-pipe control is   distributed to all the nodes (including CSRs and hosts/edge devices)   or restricted to specific nodes.   In the case of the distributed trigger, every node is regarded as   having a capability of detecting a trigger of Bypass-pipe setup or   termination.  For example, every node detects datagrams for ftp, and   sets up (or fetches) a Dedicated-VC individually to construct a   Bypass-pipe.  After setting up or fetching the Dedicated-VCs,   messages which informs (or requests) the transmission of the IP flow   over the Dedicated-VC are exchanged between adjacent nodes.  That   enables peer nodes to share the same knowledge about the mapping   relationship between the IP flow and the Dedicated-VC.  There is no   end-to-end message transmission in the Bypass-pipe control procedure   itself, but transmission between adjacent nodes only.   In the case of the centralized (or restricted) trigger, capability of   detecting a trigger of Bypass-pipe setup or termination is restricted   to nodes which are located at "the boundary of the CSR-cloud".  The   boundary of the CSR-cloud signifies, for individual IP flows, the   node which is the first-hop or the last-hop CSR-capable node.  For   example, a node which detects datagrams for ftp can initiate Bypass-   pipe setup procedure only when its previous hop is non-ATM or CSR-   incapable.  In this case, Bypass-pipe control messages are originated   at the boundary of the CSR-cloud, and forwarded hop-by-hop toward   another side of the boundary, which is similar to ATM signaling   messages.  The semantics of the messages may be the request of end-   to-end Bypass-pipe setup as well as notification or request of   mapping relationship between the IP flow and the Dedicated-VC.Katsube, et. al.             Informational                     [Page 15]

RFC 2098          Toshiba's Router Extension for ATM       February 1997b) Upstream-initiated control vs. Downstream-initiated control   The second item to be discussed is whether the setup of a Dedicated-   VC and the control procedure for constructing a Bypass-pipe are   initiated by upstream side or downstream side.   In the case of the upstream-initiated control, the upstream node   takes the initiative when setting up a Dedicated-VC for a specific IP   flow and creating the mapping relationship between the IP flow and   the Dedicated-VC.  For example, a CSR which detects datagrams for ftp   sets up (or fetches) a Dedicated-VC toward its downstream neighbor   and notifies its downstream neighbor that it will transmit a specific   IP flow over the Dedicated-VC.  This means that the downstream node   is requested to receive datagrams from the Dedicated-VC.   In the case of the downstream-initiated control, the downstream node   takes the initiative when setting up a Dedicated-VC for a specific IP   flow and creating the mapping relationship between the IP flow and   the Dedicated-VC.  For example, a CSR which detects datagrams for ftp   sets up (or fetches) a Dedicated-VC toward its upstream neighbor and   requests its upstream neighbor to transmit a specific IP flow over   the Dedicated-VC.  This means that the upstream node is requested to   transmit the IP flow over the Dedicated-VC.c) Hard-state management vs. Soft-state management   The third item to be discussed is whether the control (setup,   maintain, and release) of the Bypass-pipe is based on hard-state or   soft-state.   In hard-state management, individual nodes transmit Bypass-pipe   control messages only when they want to notify or request any change   in their neighbors' state.  They should wait for an acknowledgement   of the message before they change their internal state.  For example,   after setting up a Bypass-pipe, it is maintained until either of a   peer nodes transmits a message to release the Bypass-pipe.   In soft-state management, individual nodes periodically transmit   Bypass-pipe control messages in order to maintain their neighbors'   state.  They do not have to wait for an acknowledgement of the   message before they changes its internal state.  For example, even   after setting up a Bypass-pipe, either of a peer nodes is required to   periodically transmit refresh messages to its neighbor in order to   maintain the Bypass-pipe.5.  Security Considerations   Security issues are not discussed in this memo.Katsube, et. al.             Informational                     [Page 16]

RFC 2098          Toshiba's Router Extension for ATM       February 19976.  Summary   Basic concept of Cell Switch Router (CSR) are clarified and control   architecture for CSR is discussed.  A number of methods to control   Bypass-pipe will be possible each of which has its own advantages and   disadvantages.  Further investigation and discussion will be   necessary to design control protocol which may depend on the   requirements by users.7.  References   [IPMC96] Armitage, G., "Support for Multicast over UNI 3.0/3.1 based   ATM Networks",RFC 2022, November 1996.   [ATM3.1] The ATM-Forum, "ATM User-Network Interface Specification,   v.3.1", Sept. 1994.   [RSVP13] Braden, R., et al., "Resource ReSerVation Protocol (RSVP),   Version 1 Functional Specification", Work in Progress.   [IPNNI96] R. Callon, et al., "Issues and Approaches for Integrated   PNNI", The ATM Forum Contribution No. 96-0355, April 1996.   [NHRP09]  Luciani, J., et al., "NBMA Next Hop Resolution Protocol   (NHRP)", Work in Progress.   [PNNI1.0] The ATM-Forum, "P-NNI Specification Version 1.0", March   1996.   [RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM   Adaptation Layer 5",RFC 1483, July 1993.   [RFC1577] Laubach, M., "Classical IP and ARP over ATM",RFC 1577,   October 1993.   [RFC1819] Delgrossi, L, and L. Berger, "Internet STream Protocol   Version 2 (STII) Protocol Specification Version ST2+",RFC 1819,   August 1995.Katsube, et. al.             Informational                     [Page 17]

RFC 2098          Toshiba's Router Extension for ATM       February 19978.  Authors' Addresses   Yasuhiro Katsube   R&D Center, Toshiba   1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210   Japan   Phone : +81-44-549-2238   EMail : katsube@isl.rdc.toshiba.co.jp   Ken-ichi Nagami   R&D Center, Toshiba   1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210   Japan   Phone : +81-44-549-2238   EMail : nagami@isl.rdc.toshiba.co.jp   Hiroshi Esaki   R&D Center, Toshiba   1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210   Japan   Phone : +81-44-549-2238   EMail : hiroshi@isl.rdc.toshiba.co.jpKatsube, et. al.             Informational                     [Page 18]