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rfc:rfc2098

Network Working Group Y. Katsube Request for Comments: 2098 K. Nagami Category: Informational H. Esaki

                                                   Toshiba R&D Center
                                                        February 1997
    Toshiba's Router Architecture Extensions for ATM : Overview

Status 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

  1. It makes the best use of ATM's property while retaining current

router-based internetworking and routing architecture.

  1. 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:
  1. 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
  1. When you neither require a certain QoS nor transmit large amount of

IP datagrams for some communication

  1. When the direct ATM connection is not allowed by security or policy

reasons

2) 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.
  1. 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.
  1. 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 subnetwork

Katsube, 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 CSR

3.2 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 over

Katsube, 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 and

Katsube, 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,
  1. 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

  1. 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 1997

4.3 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 whether

Katsube, 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 from

Katsube, 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 in RFC1483 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,
  1. 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.
  1. 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 1997

b) 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 1997

6. 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 1997

8. 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.jp

Katsube, et. al. Informational [Page 18]

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