Subject: Internet-D. co/cl ip over atm

From: [email-masked] (Hiroshi Esaki)
Date: Wed, 1 Mar 1995 22:50:43 -0500

Hi all, 

 The attached Internet-Draft will be soon put in IETF directry. 

 We intend to discuss this Internet-Draft at colip-BoF in April 
 meeting, as one of discussion items.  

 >> Tuesday, April 4, 1995
 >>   1300-1500
 >> TSV CO and CL IP Transport over ATM BOF                     

 The proposed architectural framework will be able to work over 
 all of architectural models discussed in IETF associated with ATM. 
 Though this proposal is an other alternative for NHRP approach, 
 this approach will also work for the routers in NHRP-based NBMA 
 platform. 

 Regards, 

 Yasuhiro Katsube 
 Hiroshi Esaki 
 (Toshiba Corp.) 

    ----------------- included Internet-Draft -----------------

Internet Draft                                          Yasuhiro Katsube
                                                         Ken-ichi Nagami
                                                           Hiroshi Esaki
                                                    (Toshiba R&D Center)

                                                         March 1st, 1995

         Router Architecture Extensions for ATM : Overview 
           <draft-katsube-router-atm-overview-00.txt>                

Status of this memo 

   This document is an Internet-Draft.  Internet-Drafts are working 
   documents of the Internet Engineering task Force (IETF), its areas, 
   and its working groups.  Note that other groups may also distribute 
   working documents as Internet-Drafts. 

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference 
   material or to cite them other than as "work in progress". 

   To learn the current status of any Internet-Draft, please check the
   "1id-abstract.txt" listing contained in the Internet-Drafts Shadow
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   munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
   ftp.isi.edu (US West Coast).

Abstract 

   This memo describes new internetworking architecture which makes 
   better use of the property of ATM.  IP datagrams are transferred 
   along hop-by-hop path via routers similar to the Classical IP Model
   [RFC1577], 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.  
   CSR can concatenate one incoming VC and another outgoing VC in order
   to provide a certain communication with an ATM level connectivity 
   even when its endpoints do not share a common IP address prefix. 

   Proposed architecture can provide applications with desired QOS and 
   as much bandwidth as current ATM switch networks provide while 
   retaining current router-based internetworking concept.  In addition,
   it is interoperable with IP level resource reservation protocol such
   as RSVP. 

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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.  Both approaches do 
   not seem to take each other's approach into account although 
   integration or interworking of them may 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" which has the following properties.

    - It makes the best use of ATM's property while retaining current
      router-based internetworking and routing architecture. 

    - It takes into account intereoperability 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 various issues which would have close 
   relationship to the design of the detailed architecture. 

2.  Backgrounds and Motivations 

   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
   desired quality.  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 

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   delay characteristics let us to investigate the realization of IP
   datagram transmission over ATM.  

   A typical internetworking architecture specified by IETF IPoverATM WG
   is "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 due to IP header processing at every 
   router.  It will become more critical when multimedia applications 
   that require much larger bandwidth and smaller latency will become 
   dominant in the near future. 

   Another internetworking model is currently under discussion in IETF 
   ROLC WG[KAT94] and the ATM Forum Multiprotocol-over-ATM SWG.  The 
   model, that we call "NHRP (Next Hop Resolution Protocol) Model" here,
   aims at resolving throughput and latency problems in the Classical IP
   Model and making the best use of the ability 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 entity of Next Hop Server[KAT94] 
   (or Route Server) 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 will be 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]  IP datagram forwarding function and 
   routing protocol processing function, both of which are provided by 
   conventional routers, are distributed to the ATM cloud and server(s)
   respectively.  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 that go beyond IP subnet boundaries. 

   In this model, ATM is utilized not only as a datalink function but 
   also as a replacement of current hop-by-hop IP forwarding function. 
   However, 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: 

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   - 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[REK95]

   - 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 STII[STII] and RSVP[RSVP]. 

   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 its flow spec. 

   RSVP itself is not a connection oriented technology since datagrams
   can be transmitted regardless of the result of resource reservation 
   process.  After a resource reservation process from a receiver 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 its flow spec. 

   Neither STII nor RSVP 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
   datalink 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. 

   Taking these backgrounds into consideration, we should be aware of 
   several issues which motivate our proposal. 
	
   - ATM specific internetworking architecture proposed as NHRP model 
     [KAT94] does not take into account an interoperability with IP 
     level resource reservation or connection setup protocols. 
     Especially emulating RSVP in the NHRP-based ATM cloud seems to
     require much effort since RSVP is soft-state, receiver-oriented 

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     protocol.

   - Although STII or RSVP-based routers will provide each IP flow with
     a desired bandwidth and QOS, they have some native throughput
     limitations due to processor-based IP forwarding mechanism compared
     with the switching mechanism of ATM.  

   Main objective of our proposal is to resolve above issues.  Proposed
   internetworking architecture makes the best use of the property of 
   ATM by extending legacy routers which can also handle future IP such
   as flow support and resource reservation in the future. 

3.  Internetworking Architecture Based On Cell Switch Router 

3.1  Overview 

   Cell Switch Router (CSR) is a key network element of the proposed 
   internetworking architecture.  The CSR provides cell switching 
   function in addition to conventional IP datagram forwarding.  
   Communications with high throughput and small latency, that are 
   native property of ATM, become possible by using this cell switching
   function even when the communications pass through IP subnetwork 
   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 are 
   worth doing that (e.g., communications which require certain amount
   of bandwidth and QOS), while hop-by-hop datagram forwarding based on
   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 VPI/VCIs, although the 
   concatenation in this case is controlled outside the ATM cloud unlike
   conventional ATM switch nodes.  By carrying out such VPI/VCI 
   concatenations at multiple CSRs consecutively, native ATM pipe 
   composed of multiple ATM connections, each of which connects adjacent
   CSRs (and 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. 

   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 is referred as "Conventional Model" in [OHTA94]
   [ESAKI94] which would be straightforward in discussing CSR, but CSR
   is also applicable to the former configuration as well. 

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   Two different kinds of ATM VCs are defined between adjacent CSRs or 
   between CSR and ATM-attached hosts/routers. 

1) Default-VC

   It is general purpose VC used by any communications which select 
   conventional hop-by-hop IP processed route.  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 to be concatenated with other Dedicated-VCs and 
   constitutes ATM Bypass-pipe for certain communications.  The number
   of Dedicated-VCs necessary between adjacent two nodes is the same as
   the number of Bypass-pipes which pass through these nodes. 

   Ingress/egress nodes of the Bypass-pipe can be either CSRs or ATM-
   attached routers/hosts which understand 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 understand Bypass-pipe control protocol. 

   Route for a Bypass-pipe is determined when it is set up based on IP
   routing table in each CSR.  In figure 1, IP datagrams from source 
   host or router X.1 to destination host or router Z.1 are transferred
   over the route X.1 -> CSR1 -> CSR2 -> Z.1 regardless of whether the
   communication is 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 protocol [IISP][PNNI], and would be independent
   of IP level routing.  

   An example of an IP datagram transmission mechanism is as follows.

   o The host/router X.1 checks an identifier of each IP datagram, 
     which may be "destination IP address (prefix)", 
     "source/destination IP address (prefix) pair", "destination IP 
     address and port ID", "source IP address and Flow label (in 
     IPv6)", and so on.  Based on either of those identifier, it 
     determines over which VC the datagram should be transmitted. 

   o The CSR 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

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     forwarded to the specified interface through 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 then forwarded to an appropriate 
     outgoing interface/VPI/VCI.  

        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 

   Main feature of the proposed CSR-based internetworking architecture
   is the same as that of NHRP-based architecture in the sense that 
   they both provide direct ATM level connectivity beyond IP subnet 
   boundaries.  There are, however, several remarkable differences in 
   the CSR-based architecture from NHRP-based architecture as follows.

 1) Relationship between IP routing and ATM routing 

   In 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 IISP[IISP] or PNNI phase1[PNNI] while the IP routing will be
   based on conventional one such as OSPF/BGP.  We need to manage two 

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   different routing protocols over the large ATM cloud until 
   Integtrated-PNNI[IPNNI] which takes both ATM level metric and IP 
   level metric into account will be phased in.

   In 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 intra-subnet level path for ATM-VCs (both Dedicated-VC and
   Default-VC) only between adjacent nodes (CSRs or ATM-attached 
   hosts/routers).  Since roles of routing are hierarchically subdevided
   into IP level (router level) and ATM level (ATM SW level), ATM 
   routing does not have to manage all over the ATM cloud but only 
   individual IP subnets independent from each other.  This will 
   decrease the amount of information for ATM routing protocol handling.

 2) Dynamic routing and redundancy support 

   CSR-based network can dynamically change routes for Bypass-pipes when
   related IP level routing information changes.  Ingress points of 
   these Bypass-pipes (ATM-attached sender hosts or routers) do not have
   to be aware of such dynamic change of routes since 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 error or outage would change routes for related Bypass-
   pipes by themselves. 

 3) Support of hard-state and soft-state control

   Although direct ATM-VCs in NHRP model are controlled by ATM signaling
   which is hard-state protocol, Bypass-pipes provided by CSR-based 
   network are controlled by dedicated protocols which can be both 
   hard-state and soft-state.  A motivation of the support of soft-state
   in Bypass-pipe control is an interworking with RSVP protocol. 
   Soft-state protocol will be much more suited to the realization of 
   dynamic routing described in 2). 

4) Support of sender-initiated and receiver-initiated control 

   Although setup of direct ATM-VCs in NHRP model is sender-initiated 
   only, setup of Bypass-pipes in CSR model can be either sender-
   initiated or receiver-initiated.  Detailed procedures for receiver-
   initiated protocol will be designed to handle RSVP messages. 

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4.  Discussions for Designing Detailed Architecture

   Several issues that need further investigations in order to design
   detailed architecture are discussed in this section. 

4.1  Network Reference Model 

   In order to help understanding discussions in this section, the
   following network reference model are assumed.  Source hosts S1, S2,
   and destination hosts D1, D2 are attached to Ethernet, while S3 and 
   D3 are attached to ATM.  Routers R1 and R5 are attached to Ethernet
   only, while R2, R3 and R4 are attached to ATM.  ATM datalink for 
   subnet #3 and subnet #4 can either be physically separated datalinks
   or be the same datalink. 

   Bypass-pipes can be set up [S3 or R2]-->R3-->[D3 or R4].  That means 
   that S3, D3, R2, R3 and R4 need to speak Bypass-pipe control protocol
   described later, and means that R3 needs to be a 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 set up 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). 

      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 

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4.2  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.  Each 
   Dedicated-VC is released when the corresponding Bypass-pipe is 
   released. 

b) Picking up one from a bunch of (semi-)PVCs 

   Several Dedicated-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.  A sort of "Unused VC list" will
   be managed by a peer nodes which share these PVCs.  

c) Picking up one VCI in PVP/SVP

   A 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 kind of 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.  A sort of "Unused VC list" will be managed by the peer nodes
   which share the PVP/SVP.  The SVP can be released through ATM 
   signaling when no VCI value is active state.  That may require some 
   revision to RFC1577. 

   The best choice will be a) with regard to efficient network resource 
   usage.  However, you may go through three steps, ATMARP (in each IP 
   subnet), SVC setup (in each IP subnet) and Bypass-pipe setup in this
   case.  Whether a) is practical choice or not will depend on whether 
   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 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 

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   or ATM-attached host/router) should specify some traffic descriptors
   even for unused VCs, and the ATM datalink should reserve its resired
   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.  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 function of the ATM datalink but of each CSR or ATM-attached
   host/router if necessary.  Only function which need to be provided by
   the ATM datalink is control of VPs' bandwidth such as UPC and dynamic
   bandwidth negotiation if necessary. 

   As a result of the above observations, we will implement c) as a
   preliminary protocol specification, but may add a) in the future 
   version if it is desirable.  

4.3  Channels for Bypass-pipe Control Message Transfer

   There are several alternatives regarding the protocol for managing 
   (setting up and releasing) a Bypass-pipe.  This subsection explains 
   these alternatives and discusses their properties from various 
   viewpoints. 

   Among alternatives of how to provide Dedicated-VCs described in 4.2, 
   "picking up an unused VCI in PVP/SVP" is assumed.  When we use "on-
   demand SVC setup", Dedicated-VC setup in each subnet through ATM 
   signaling (and possibly ATMARP before that) will be added to the 
   following procedures.  An alternative described in iii), however, 
   investigates a possibility of managing Bypass-pipes by only extending
   ATM signaling messages, and of excluding the necessity of additional 
   control messages. 

   Three alternatives are discussed, Inband message protocol, Outband 
   message protocol, and ATM signaling extension. 

i) Inband Control Message 

   When setting up a Bypass-pipe, control messages are transmitted over
   an unused Dedicated-VC which will eventually be used as a component 
   of the Bypass-pipe.  These messages are handled at each CSR and 
   forwarded over an unused Dedicated-VC along the selected route 
   (based on IP routing table) for the requested Bypass-pipe.  Unlike 
   outband message protocol described in ii), each message does not have
   to indicate VCI value used as a Dedicated-VC since the message itself
   is carried by that VC.  That leads to a possibility that existing 
   messages such as STII, RSVP, or NHRP messages itself can be utilized

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   as a Bypass-pipe control message with no modification.  However, 
   there are following shortcomings;

   - Bypass-pipe control messages transmitted after a Bypass-pipe has 
     been set up (e.g., Bypass-pipe release) cannot be identified at 
     intermediate CSRs since those messages are forwarded at cell level
     there. 

   - Bypass-incapable routers (routers which does not understand Bypass-
     pipe control protocol) would not receive and process cells 
     transmitted over "unknown VCI".  That means that Bypass-pipe 
     management massages will be discarded by Bypass-incapable routers. 

   We can manage to find solutions for the former issue.  That is, 
   intermediate CSRs can identify Bypass-pipe control messages by 
   marking cell headers, e.g., PTI bit on indicating F5 OAM cell.  It 
   would be difficult, however, to find solutions for the latter issue.
   As a  result of these observations, Inband message will not be 
   adequate as a Bypass-pipe control. 

ii) Outband Control Message 

   When both setting up and releasing a Bypass-pipe, control messages
   are transmitted over VCs which are different from Dedicated-VCs used
   as components of the Bypass-pipe.  Although each message has to 
   indicate VCI value used as a Dedicated-VC, which means that STII or
   RSVP messages received from conventional routers/hosts cannot be
   utilized as a Bypass-pipe control messages as they are, the 
   shortcomings in inband case do not exist. 

   Three 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.

   When we take into account interoperability with Bypass-incapable 
   routers, 1) will not be a good choice.  Whether we select 2) or 3) 
   depends on whether we should consider multiprotocol rather than IP 
   only.  We select 3) as a preliminary protocol specification. 

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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 Call 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, and possibly their port IDs, 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.  
   Then it transmits an ATM signaling message to the ATM network in 
   order to forward Bypass-pipe setup request to the next-hop IP node as
   well as to request Dedicated-VC setup to that.  

   Examples of Bypass-pipe setup procedure are shown in figure 3.  

                     ATM                  ATM     
                +----------+          +----------+   
                |          |          |          |    
           S3---|  ATM-SW  |          |  ATM-SW  |---D3
                |    |X|   |          |    |X|   |    
        ---R2---|          |----R3----|          |---R4---
                +----------+          +----------+    
                   subnet                subnet 
                     #3                    #4

              Setup     Setup       Setup     Setup
             (S3-R3)   (S3-R3)     (R3-D3)   (R3-D3)
       (Trg)|------>|-|------>|---|------>|-|------>|
            |<------|-|-------|---|<------|-|-------|
              Conn      Conn        Conn      Conn

              Setup     Setup       Setup     Setup
             (S3-R3)   (S3-R3)     (R3-D3)   (R3-D3)
       (Trg)|------>|-|------>|-+-|------>|-|------>|
            |<------|-|-------|-+ |<------|-|-------|
              Conn      Conn        Conn      Conn

                                         (Trg) : Trigger event for 
                                                 Bypass-pipe setup
                 
             Figure 3  Use of ATM Signaling Messages 

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   A difference of the two examples is whether a CONNECT message means 
   confirmation of Bypass-pipe setup or confirmation of Dedicated-VC 
   setup.  The problems of 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 standard. 

    - It would be difficult to support soft-state operation since ATM
      signaling is naturally a hard-state protocol. 

   As a result of above observations, we will select ii) as a 
   preliminary protocol specification, while the possibility of iii) 
   will be further study issue. 

4.4  Triggers for Bypass-pipe Setup/Release 

   This subsection discusses several possible events which triggers a 
   node to set up or release a Bypass-pipe.  

4.4.1  Triggers for Bypass-pipe Setup

   As of now, following two cases should be taken into account as 
   triggers for Bypass-pipe setup.  

   1) Request by IP layer or upper layers of an end host

   2) Decision by a Bypass-capable router based on the measurement of IP
      datagrams transmitted. 

   The case 1) is further classified into the cases in which the request
   is initiated by a sender-host or a receiver-host, and the cases in 
   which the request is initiated by a Bypass-capable host or a Bypass-
   incapable host.  Therefore we should take the following four cases 
   into account. (see figure 2)

   1-1) Request by Bypass-capable sender-host (S3)

   1-2) Request by Bypass-incapable sender-host (S1, S2)

   1-3) Request by Bypass-capable receiver-host (D3)

   1-4) Request by Bypass-incapable receiver-host (D1, D2)

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   For simplicity, we mean that the Bypass-(in)capable node is equal to
   ATM-(non)attached node in figure 2, but there may be the case that an
   ATM-attached node does not support Bypass-pipe control protocol. 

   In the case of 1-1) or 1-3), sender-host(S3) or receiver-host(D3) 
   itself executes Bypass-pipe setup protocol.  IP layer or upper layers
   in S3 or D3 requests Bypass-pipe setup to its own Bypass management 
   entity directly, or via other QOS/Resource management entity such as 
   STII (in the case of sender-host) or RSVP (in the case of receiver-
   host).  Resulting Bypass-pipe will finally be S3-->R3-->D3 in this 
   case. 

   In the case of 1-2) or 1-4), neither sender-host(S1, S2) nor 
   receiver-host (D1, D2) has Bypass management entity.  IP layer or 
   upper layers in S1/S2 or D1/D2 requests resource reservation to its 
   own QOS/Resource management entity such as STII or RSVP.  Then it 
   transmits IP level resource reservation messages over whatever
   datalink network (Ethernet in figure 2).  A Bypass-capable router R2
   or R4 which has received those messages either translates those IP 
   level resource reservation messages to Bypass-pipe control messages
   or encapsulates those messages in Bypass-pipe control messages.  In 
   any case, Bypass-pipe management entities in R2 or R4 initiates 
   Bypass-pipe setup procedures triggered by IP level resource 
   management messages from S1/S2 or D1/D2.  Resulting Bypass-pipe will
   finally be R2-->R3-->R4 in this case.

   In the case of 2), a Bypass-capable router R2 initiates Bypass-pipe 
   setup procedures with its own decision based on the measurement of IP
   datagrams transmitted toward a certain destination host or network.  
   Unlike case 1), the purpose of setting up Bypass-pipe in case 2) is 
   to reduce IP processing burden at intermediate CSRs rather than to 
   provide end hosts or applications with desired bandwidth/QOS.  For 
   example, when R2 detects large amount of datagrams bound for IP 
   subnet #6, it may initiates Bypass-pipe setup with its destination 
   set to subnet#6.  Resulting Bypass-pipe will finally be R2-->R3-->R4
   in this case.  Whether the use of this Bypass-pipe is limited to the 
   communication destined to subnet#6 or is open to communications 
   destined to other networks (e.g., subnet#5) depends on whether the 
   information about the Bypass-pipe is advertized as a routing 
   information, and requires further study. 

4.4.2  Triggers for Bypass-pipe Release 

   The same items as the case of Bypass-pipe setup applies to Bypass-
   pipe release, 1) and 2).  However, 1) will have variations of whether
   IP level resource reservation protocol which is running in Bypass-
   incapable hosts is hard-state (STII) or soft-state (RSVP).  Bypass-

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   pipe release can be initiated at R2 or R4 by the reception of 
   explicit IP level resource release messages in both cases, and by the
   detection of "no resource keep message" for a predetermined timeout 
   period in the case of soft-state.  Detailed discussion will be given
   later. 

   It should be noted that the trigger for setup/release of Bypass-pipe
   is not limited to examples given in this subsection although we 
   assume them in specifying version 1 protocol.  Actual Bypass-pipe 
   control protocol, therefore, should not be dependent on what the 
   trigger is.  

4.5  Bypass-pipe Control Protocol 

   It  is desirable that the Bypass-pipe can be set up in response to 
   triggers at least described in 4.4.  That is, a Bypass-capable node 
   (host or router) should initiate Bypass-pipe setup when, 

   - It (router) has received IP level resource reservation messages 
     from its upstream (e.g., STII) or downstream (e.g., RSVP) node.
     [1-2) or 1-4) in 4.4]

   - It (host) has received IP level resource reservation primitives 
     from its own IP level resource reservation entities such as STII 
     or RSVP. 
     [1-1) or 1-3) in 4.4]

   - It (router) has decided to set up a Bypass-pipe for a 
     communication to a certain host or network based on the result of
     IP level traffic measurement. 
     [2) in 4.4] 

   Taking them into account, the protocol should be designed to support

    - both hard-state (STII) and soft-state (RSVP) control
    - both sender-initiated (STII) and receiver-initiated (RSVP) control

   Since currently available IP level protocols are sender-initiated 
   hard-state (STII) and receiver-initiated soft-state (RSVP), we 
   investigate brief examples of those two as a preliminary protocol 
   specification. 

4.5.1  Sender-Initiated Hard-State Control 

   Examples of sender-initiated hard-state control protocol are shown in

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   figure 4.  A Bypass-capable node (R2 or S3) which has been triggered
   by an upstream node (S1 or S2) or by an internal entity (S3) 
   transmits a Bypass-pipe setup message (BP-Setup) toward target 
   destination node which may or may not be Bypass-capable. 

   BP-Setup includes at least target host or network address, identifier
   of a Bypass-pipe which is being set up, identifier of a Dedicated-VC 
   which is being used as a component of the Bypass-pipe, and desirable 
   bandwidth.  A node which has received BP-Setup from the previous node
   obtains next-hop node based on IP routing table, decides whether 
   requested bandwidth is available to the obtained node, and picks up 
   an available Dedicated-VC to the node when the bandwidth is 
   available.  Then it transmits BP-Setup to the next-hop node over a 
   Default-VC.  This procedure is repeated all the way to the target 
   node until whether the BP-Setup reaches the target node or some 
   intermediate node recognizes that it cannot extend Bypass-pipe 
   anymore (e.g., by the policy restriction or bandwidth shortage).  
   Such a node creates a Bypass-pipe setup ack message (BP-SetupAck) 
   over the reverse route toward the requesting node.  Bypass-pipe setup
   procedure completes when the BP-SetupAck has returned to the 
   requesting node.  

                       ATM                ATM     
                   +---------+        +---------+   
                   |         |        |         |   
              S3---|         |        |         |---D3
                   |         |        |         |    
           ---R2---|         |---R3---|         |---R4---
                   |         |        |         |    
                   +---------+        +---------+    
                      subnet            subnet    
                        #3                #4      

   [Setup]           BP-Setup          BP-Setup
           (Trg)|-------------->|--|-------------->|
                |<--------------|--|<--------------|
                   BP-SetupAck        BP-SetupAck 
 
  [Release]        BP-Release         BP-Release
           (Trg)|-------------->|  |-------------->|
                |<--------------|  |<--------------|
                    BP-RelAck          BP-RelAck

                                            (Trg): Trigger event for
                                                   Bypass-pipe setup

          Figure 4  Sender-Initiated Hard-State Control

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   With regard to Bypass-pipe release, BP-Release message is issued by 
   either of nodes on the route of the Bypass-pipe by its own trigger or
   by the indirect trigger (e.g., the reception of STII Disconnect from 
   Bypass-incapable host which uses the Bypass-pipe).  

4.5.2  Receiver-Initiated Soft-State Control

   Examples of receiver-initiated soft-state control protocol are shown
   in figure 5.  In soft-state, sender node periodically transmits Path 
   messages (BP-Path) over the Default-VC forward along the route 
   specified by the IP routing table.  These BP-Path messages are 
   necessary in order that the resource reservation messages (BP-Resv)
   transmitted by the receiver node are routed in the reverse direction
   toward the sender node. 

   A Bypass-capable node which has been triggered by a downstream node 
   or by an its internal entity transmits a resource reservation message
   (BP-Resv) toward the sender node along the reverse route given by the
   BP-Path. 

   Contents of the BP-Resv message will be the same as that of the RSVP 
   Resv message with the addition of Bypass-pipe specific information 
   such as an identifier of a Dedicated-VC which is being used as a 
   component of the Bypass-pipe.  A node which has received BP-Resv from
   the downstream node obtains previous-hop node based on the Path state
   given by the BP-Path messages, decides whether requested bandwidth to
   the previous node is available, and picks up an available Dedicated-
   VC to that node.  Then it transmits the BP-Resv to that node over a 
   Default-VC.   This procedure is repeated all the way to the sender 
   node.  If the BP-Resv message fails to be transmitted at an 
   intermediate node, that node would become an ingress point of the 
   Bypass-pipe or send back an error message. 

   After setting up a Bypass-pipe, the sender node still continues to 
   send BP-Path messages, and the receiver node continues to send BP-
   Resv messages periodically.  When individual nodes along the Bypass-
   pipe route have not received BP-Resv messages for a predetermined 
   timeout period, they would decide that the Bypass-pipe can be 
   released.  The Bypass-pipe can be released by an explicit Teardown 
   message as well as the above-mentioned timeout-based release. 

   When some IP routing change happens to nodes related to a Bypass-
   pipe, BP-Path messages will be automatically transferred along the 
   new route.  BP-Resv messages from the receiver node then will be sent
   back along the new route, that will lead to removal of the Bypass-
   pipe from old route and creation of the Bypass-pipe over the new 
   route. 

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                       ATM                ATM     
                   +---------+        +---------+   
                   |         |        |         |   
              S3---|         |        |         |---D3
                   |         |        |         |    
           ---R2---|         |---R3---|         |---R4---
                   |         |        |         |    
                   +---------+        +---------+    
                      subnet            subnet    
                        #3                #4      

   [Setup]           BP-Path           BP-Path
                |-------------->|--|-------------->|
                |<--------------|--|<--------------|(Trg)
                |    BP-Resv    |  |   BP-Resv     |
                |               |  |               |
               %%% Communications over Bypass-pipe %%%
   [Keep]       |               |  |               |
                |   BP-Path     |  |   BP-Path     |
                |-------------->|--|-------------->|
                |<--------------|--|<--------------|
                |   BP-Resv     |  |   BP-Resv     |
 
                                           (Trg): Trigger event for
                                                  Bypass-pipe setup

         Figure 5   Receiver-Initiated Soft-State Control

5.  Security Considerations 

   Security issues are not discussed in this memo. 

6.  Open Issues

   o Detailed protocol sequences and proposed message formats. 
     It should be interoperable with conventional IP level resource
     management protocols such as STII and RSVP. 

   o Mapping of IP level filter specs to ATM cell level control
     mechanisms, especially in multicast cases. 

   o Do we support any combination of both hard-state/soft-state and
     sender-initiated/receiver-initiation control? 

   o Support of source route option on the CSR-based network. 

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7.  References 

   [ATM3.1] The ATM-Forum, "ATM User-Network Interface Specification,
   v.3.1", Sept. 1994. 

   [ESAKI94] H. Esaki, et al., "Connection Oriented and Connectionless
   IP Forwarding over ATM Networks", IETF Internet Draft (work in 
   progress), draft-esaki-co-cl-ip-forw-atm-01.txt, Oct. 1994. 

   [IISP] The ATM-Forum, "Interim Inter-switch Signaling Protocol (IISP)
   Protocol Specification, Version 1.0", Dec. 1994.

   [IPNNI] R. Callon, "Integrated PNNI for Multi-Protocol Routing", The
   ATM Forum Contribution No. 94-0789, Sept. 1994. 

   [KAT94]  D. Katz and D. Piscitello, "NBMA Next Hop Resolution 
   Protocol(NHRP)", IETF Internet Draft (work in progress), draft-ietf-
   rolc-nhrp-03.txt, Nov. 1994. 

   [OHTA94] M. Ohta, et al., "Conventional IP over ATM", IETF Internet
   Draft (work in progress), draft-ohta-ip--over-atm-01.txt, July 1994.

   [PNNI] The ATM-Forum, "P-NNI Draft Specification R5", Jan. 1995. 

   [REK95] Y. Rekhter and D. Kandlur, "IP Architecture Extensions over
   ATM", IETF Internet Draft (work in progress), draft-rekhter-ip-atm-
   architecture.txt, Jan. 1995. 

   [RFC1483] J. Heinanen, "Multiprotocol Encapsulation over ATM
   Adaptation Layer 5", IETF RFC 1483, July 1993. 

   [RFC1577] M. Laubach, "Classical IP and ARP over ATM", IETF RFC 1577,
   Oct. 1993. 

   [RSVP] L. Zhang, et al., "Resource ReSerVation Protocol (RSVP), 
   Version 1 Functional Specification", IETF Internet Draft (work in 
   progress), draft-ietf-rsvp-spec-04.ps, Nov. 1994. 

   [STII] L. Delgrossi and L. Berger, "Internet STream Protocol Version
   2(STII)", Internet Draft (work in progress), 
   draft-ietf-st2-spec-02.ps, Feb. 1995. 

8.  Authors' Address

   Yasuhiro Katsube
   R&D Center, Toshiba 
   1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210

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   Japan 
   Phone : +81-44-549-2238
   Email : [email-masked]

   Ken-ichi Nagami
   R&D Center, Toshiba 
   1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210
   Japan 
   Phone : +81-44-549-2238
   Email : [email-masked]

   Hiroshi Esaki
   R&D Center, Toshiba
   801 Schapiro Research Building, c/o CTR, Columbia Univ.
   530 West, 120th St., New York, NY 10027
   Phone : 212-854-2365
   Email : [email-masked]

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