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Network Working Group                                 E. Crawley, EditorRequest for Comments: 2382                                Argon NetworksCategory: Informational                                        L. Berger                                                            Fore Systems                                                               S. Berson                                                                    ISI                                                                F. Baker                                                           Cisco Systems                                                               M. Borden                                                            Bay Networks                                                             J. Krawczyk                                               ArrowPoint Communications                                                             August 1998A Framework for Integrated Services and RSVP over ATMStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1998).  All Rights Reserved.Abstract   This document outlines the issues and framework related to providing   IP Integrated Services with RSVP over ATM. It provides an overall   approach to the problem(s) and related issues.  These issues and   problems are to be addressed in further documents from the ISATM   subgroup of the ISSLL working group.1. Introduction   The Internet currently has one class of service normally referred to   as "best effort."  This service is typified by first-come, first-   serve scheduling at each hop in the network.  Best effort service has   worked well for electronic mail, World Wide Web (WWW) access, file   transfer (e.g. ftp), etc.  For real-time traffic such as voice and   video, the current Internet has performed well only across unloaded   portions of the network.  In order to provide quality real-time   traffic, new classes of service and a QoS signalling protocol areCrawley, et. al.             Informational                      [Page 1]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   being introduced in the Internet [1,6,7], while retaining the   existing best effort service.  The QoS signalling protocol is RSVP   [1], the Resource ReSerVation Protocol and the service models   One of the important features of ATM technology is the ability to   request a point-to-point Virtual Circuit (VC) with a specified   Quality of Service (QoS).  An additional feature of ATM technology is   the ability to request point-to-multipoint VCs with a specified QoS.   Point-to-multipoint VCs allows leaf nodes to be added and removed   from the VC dynamically and so provides a mechanism for supporting IP   multicast. It is only natural that RSVP and the Internet Integrated   Services (IIS) model would like to utilize the QoS properties of any   underlying link layer including ATM, and this memo concentrates on   ATM.   Classical IP over ATM [10] has solved part of this problem,   supporting IP unicast best effort traffic over ATM.  Classical IP   over ATM is based on a Logical IP Subnetwork (LIS), which is a   separately administered IP subnetwork.  Hosts within an LIS   communicate using the ATM network, while hosts from different subnets   communicate only by going through an IP router (even though it may be   possible to open a direct VC between the two hosts over the ATM   network).  Classical IP over ATM provides an Address Resolution   Protocol (ATMARP) for ATM edge devices to resolve IP addresses to   native ATM addresses.  For any pair of IP/ATM edge devices (i.e.   hosts or routers), a single VC is created on demand and shared for   all traffic between the two devices.  A second part of the RSVP and   IIS over ATM problem, IP multicast, is being solved with MARS [5],   the Multicast Address Resolution Server.   MARS compliments ATMARP by allowing an IP address to resolve into a   list of native ATM addresses, rather than just a single address.   The ATM Forum's LAN Emulation (LANE) [17,20] and Multiprotocol Over   ATM (MPOA) [18] also address the support of IP best effort traffic   over ATM through similar means.   A key remaining issue for IP in an ATM environment is the integration   of RSVP signalling and ATM signalling in support of the Internet   Integrated Services (IIS) model.  There are two main areas involved   in supporting the IIS model, QoS translation and VC management. QoS   translation concerns mapping a QoS from the IIS model to a proper ATM   QoS, while VC management concentrates on how many VCs are needed and   which traffic flows are routed over which VCs.Crawley, et. al.             Informational                      [Page 2]

RFC 2382         Integrated Services and RSVP over ATM       August 19981.1 Structure and Related Documents   This document provides a guide to the issues for IIS over ATM.  It is   intended to frame the problems that are to be addressed in further   documents. In this document, the modes and models for RSVP operation   over ATM will be discussed followed by a discussion of management of   ATM VCs for RSVP data and control. Lastly, the topic of   encapsulations will be discussed in relation to the models presented.   This document is part of a group of documents from the ISATM subgroup   of the ISSLL working group related to the operation of IntServ and   RSVP over ATM.  [14] discusses the mapping of the IntServ models for   Controlled Load and Guaranteed Service to ATM.  [15 and 16] discuss   detailed implementation requirements and guidelines for RSVP over   ATM, respectively.  While these documents may not address all the   issues raised in this document, they should provide enough   information for development of solutions for IntServ and RSVP over   ATM.1.2 Terms   Several term used in this document are used in many contexts, often   with different meaning.  These terms are used in this document with   the following meaning:   - Sender is used in this document to mean the ingress point to the     ATM network or "cloud".   - Receiver is used in this document to refer to the egress point from     the ATM network or "cloud".   - Reservation is used in this document to refer to an RSVP initiated     request for resources. RSVP initiates requests for resources based     on RESV message processing. RESV messages that simply refresh state     do not trigger resource requests.  Resource requests may be made     based on RSVP sessions and RSVP reservation styles.  RSVP styles     dictate whether the reserved resources are used by one sender or     shared by multiple senders. See [1] for details of each. Each new     request is referred to in this document as an RSVP reservation, or     simply reservation.   - Flow is used to refer to the data traffic associated with a     particular reservation.  The specific meaning of flow is RSVP style     dependent. For shared style reservations, there is one flow per     session. For distinct style reservations, there is one flow per     sender (per session).2. Issues Regarding the Operation of RSVP and IntServ over ATM   The issues related to RSVP and IntServ over ATM fall into several   general classes:Crawley, et. al.             Informational                      [Page 3]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   - How to make RSVP run over ATM now and in the future   - When to set up a virtual circuit (VC) for a specific Quality of     Service (QoS) related to RSVP   - How to map the IntServ models to ATM QoS models   - How to know that an ATM network is providing the QoS necessary for     a flow   - How to handle the many-to-many connectionless features of IP     multicast and RSVP in the one-to-many connection-oriented world of     ATM2.1 Modes/Models for RSVP and IntServ over ATM   [3] Discusses several different models for running IP over ATM   networks.  [17, 18, and 20] also provide models for IP in ATM   environments.  Any one of these models would work as long as the RSVP   control packets (IP protocol 46) and data packets can follow the same   IP path through the network.  It is important that the RSVP PATH   messages follow the same IP path as the data such that appropriate   PATH state may be installed in the routers along the path.  For an   ATM subnetwork, this means the ingress and egress points must be the   same in both directions for the RSVP control and data messages.  Note   that the RSVP protocol does not require symmetric routing.  The PATH   state installed by RSVP allows the RESV messages to "retrace" the   hops that the PATH message crossed.  Within each of the models for IP   over ATM, there are decisions about using different types of data   distribution in ATM as well as different connection initiation.  The   following sections look at some of the different ways QoS connections   can be set up for RSVP.2.1.1 UNI 3.x and 4.0   In the User Network Interface (UNI) 3.0 and 3.1 specifications [8,9]   and 4.0 specification, both permanent and switched virtual circuits   (PVC and SVC) may be established with a specified service category   (CBR, VBR, and UBR for UNI 3.x and VBR-rt and ABR for 4.0) and   specific traffic descriptors in point-to-point and point-to-   multipoint configurations.  Additional QoS parameters are not   available in UNI 3.x and those that are available are vendor-   specific.  Consequently, the level of QoS control available in   standard UNI 3.x networks is somewhat limited.  However, using these   building blocks, it is possible to use RSVP and the IntServ models.   ATM 4.0 with the Traffic Management (TM) 4.0 specification [21]   allows much greater control of QoS.  [14] provides the details of   mapping the IntServ models to UNI 3.x and 4.0 service categories and   traffic parameters.Crawley, et. al.             Informational                      [Page 4]

RFC 2382         Integrated Services and RSVP over ATM       August 19982.1.1.1 Permanent Virtual Circuits (PVCs)   PVCs emulate dedicated point-to-point lines in a network, so the   operation of RSVP can be identical to the operation over any point-   to-point network.  The QoS of the PVC must be consistent and   equivalent to the type of traffic and service model used.  The   devices on either end of the PVC have to provide traffic control   services in order to multiplex multiple flows over the same PVC.   With PVCs, there is no issue of when or how long it takes to set up   VCs, since they are made in advance but the resources of the PVC are   limited to what has been pre-allocated.  PVCs that are not fully   utilized can tie up ATM network resources that could be used for   SVCs.   An additional issue for using PVCs is one of network engineering.   Frequently, multiple PVCs are set up such that if all the PVCs were   running at full capacity, the link would be over-subscribed.  This   frequently used "statistical multiplexing gain" makes providing IIS   over PVCs very difficult and unreliable.  Any application of IIS over   PVCs has to be assured that the PVCs are able to receive all the   requested QoS.2.1.1.2 Switched Virtual Circuits (SVCs)   SVCs allow paths in the ATM network to be set up "on demand".  This   allows flexibility in the use of RSVP over ATM along with some   complexity.  Parallel VCs can be set up to allow best-effort and   better service class paths through the network, as shown in Figure 1.   The cost and time to set up SVCs can impact their use.  For example,   it may be better to initially route QoS traffic over existing VCs   until a SVC with the desired QoS can be set up for the flow.  Scaling   issues can come into play if a single RSVP flow is used per VC, as   will be discussed inSection 4.3.1.1. The number of VCs in any ATM   device may also be limited so the number of RSVP flows that can be   supported by a device can be strictly limited to the number of VCs   available, if we assume one flow per VC.Section 4 discusses the   topic of VC management for RSVP in greater detail.Crawley, et. al.             Informational                      [Page 5]

RFC 2382         Integrated Services and RSVP over ATM       August 1998                             Data Flow ==========>                     +-----+                     |     |      -------------->  +----+                     | Src |    -------------->    | R1 |                     |    *|  -------------->      +----+                     +-----+       QoS VCs                          /\                          ||                      VC  ||                      Initiator                    Figure 1: Data Flow VC Initiation   While RSVP is receiver oriented, ATM is sender oriented.  This might   seem like a problem but the sender or ingress point receives RSVP   RESV messages and can determine whether a new VC has to be set up to   the destination or egress point.2.1.1.3 Point to MultiPoint   In order to provide QoS for IP multicast, an important feature of   RSVP, data flows must be distributed to multiple destinations from a   given source.  Point-to-multipoint VCs provide such a mechanism.  It   is important to map the actions of IP multicasting and RSVP (e.g.   IGMP JOIN/LEAVE and RSVP RESV/RESV TEAR) to add party and drop party   functions for ATM.  Point-to-multipoint VCs as defined in UNI 3.x and   UNI 4.0 have a single service class for all destinations.  This is   contrary to the RSVP "heterogeneous receiver" concept.  It is   possible to set up a different VC to each receiver requesting a   different QoS, as shown in Figure 2. This again can run into scaling   and resource problems when managing multiple VCs on the same   interface to different destinations.Crawley, et. al.             Informational                      [Page 6]

RFC 2382         Integrated Services and RSVP over ATM       August 1998                                    +----+                           +------> | R1 |                           |        +----+                           |                           |        +----+              +-----+ -----+   +--> | R2 |              |     | ---------+    +----+  Receiver Request Types:              | Src |                       ---->  QoS 1 and QoS 2              |     | .........+    +----+  ....>  Best-Effort              +-----+ .....+   +..> | R3 |                           :        +----+                       /\  :                       ||  :        +----+                       ||  +......> | R4 |                       ||           +----+                     Single                  IP Multicast                     Group                    Figure 2: Types of Multicast Receivers   RSVP sends messages both up and down the multicast distribution tree.   In the case of a large ATM cloud, this could result in a RSVP message   implosion at an ATM ingress point with many receivers.   ATM 4.0 expands on the point-to-multipoint VCs by adding a Leaf   Initiated Join (LIJ) capability. LIJ allows an ATM end point to join   into an existing point-to-multipoint VC without necessarily   contacting the source of the VC.  This can reduce the burden on the   ATM source point for setting up new branches and more closely matches   the receiver-based model of RSVP and IP multicast.  However, many of   the same scaling issues exist and the new branches added to a point-   to-multipoint VC must use the same QoS as existing branches.2.1.1.4 Multicast Servers   IP-over-ATM has the concept of a multicast server or reflector that   can accept cells from multiple senders and send them via a point-to-   multipoint VC to a set of receivers.  This moves the VC scaling   issues noted previously for point-to-multipoint VCs to the multicast   server.  Additionally, the multicast server will need to know how to   interpret RSVP packets or receive instruction from another node so it   will be able to provide VCs of the appropriate QoS for the RSVP   flows.Crawley, et. al.             Informational                      [Page 7]

RFC 2382         Integrated Services and RSVP over ATM       August 19982.1.2 Hop-by-Hop vs. Short Cut   If the ATM "cloud" is made up a number of logical IP subnets (LISs),   then it is possible to use "short cuts" from a node on one LIS   directly to a node on another LIS, avoiding router hops between the   LISs. NHRP [4], is one mechanism for determining the ATM address of   the egress point on the ATM network given a destination IP address.   It is a topic for further study to determine if significant benefit   is achieved from short cut routes vs. the extra state required.2.1.3 Future Models   ATM is constantly evolving.  If we assume that RSVP and IntServ   applications are going to be wide-spread, it makes sense to consider   changes to ATM that would improve the operation of RSVP and IntServ   over ATM.  Similarly, the RSVP protocol and IntServ models will   continue to evolve and changes that affect them should also be   considered.  The following are a few ideas that have been discussed   that would make the integration of the IntServ models and RSVP easier   or more complete.  They are presented here to encourage continued   development and discussion of ideas that can help aid in the   integration of RSVP, IntServ, and ATM.2.1.3.1 Heterogeneous Point-to-MultiPoint   The IntServ models and RSVP support the idea of "heterogeneous   receivers"; e.g., not all receivers of a particular multicast flow   are required to ask for the same QoS from the network, as shown in   Figure 2.   The most important scenario that can utilize this feature occurs when   some receivers in an RSVP session ask for a specific QoS while others   receive the flow with a best-effort service.  In some cases where   there are multiple senders on a shared-reservation flow (e.g., an   audio conference), an individual receiver only needs to reserve   enough resources to receive one sender at a time.  However, other   receivers may elect to reserve more resources, perhaps to allow for   some amount of "over-speaking" or in order to record the conference   (post processing during playback can separate the senders by their   source addresses).   In order to prevent denial-of-service attacks via reservations, the   service models do not allow the service elements to simply drop non-   conforming packets.  For example, Controlled Load service model [7]   assigns non-conformant packets to best-effort status (which may   result in packet drops if there is congestion).Crawley, et. al.             Informational                      [Page 8]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   Emulating these behaviors over an ATM network is problematic and   needs to be studied.  If a single maximum QoS is used over a point-   to-multipoint VC, resources could be wasted if cells are sent over   certain links where the reassembled packets will eventually be   dropped.  In addition, the "maximum QoS" may actually cause a   degradation in service to the best-effort branches.   The term "variegated VC" has been coined to describe a point-to-   multipoint VC that allows a different QoS on each branch.  This   approach seems to match the spirit of the Integrated Service and RSVP   models, but some thought has to be put into the cell drop strategy   when traversing from a "bigger" branch to a "smaller" one.  The   "best-effort for non-conforming packets" behavior must also be   retained.  Early Packet Discard (EPD) schemes must be used so that   all the cells for a given packet can be discarded at the same time   rather than discarding only a few cells from several packets making   all the packets useless to the receivers.2.1.3.2 Lightweight Signalling   Q.2931 signalling is very complete and carries with it a significant   burden for signalling in all possible public and private connections.   It might be worth investigating a lighter weight signalling mechanism   for faster connection setup in private networks.2.1.3.3 QoS Renegotiation   Another change that would help RSVP over ATM is the ability to   request a different QoS for an active VC.  This would eliminate the   need to setup and tear down VCs as the QoS changed.  RSVP allows   receivers to change their reservations and senders to change their   traffic descriptors dynamically.  This, along with the merging of   reservations, can create a situation where the QoS needs of a VC can   change.  Allowing changes to the QoS of an existing VC would allow   these features to work without creating a new VC.  In the ITU-T ATM   specifications [24,25], some cell rates can be renegotiated or   changed.  Specifically, the Peak Cell Rate (PCR) of an existing VC   can be changed and, in some cases, QoS parameters may be renegotiated   during the call setup phase. It is unclear if this is sufficient for   the QoS renegotiation needs of the IntServ models.2.1.3.4 Group Addressing   The model of one-to-many communications provided by point-to-   multipoint VCs does not really match the many-to-many communications   provided by IP multicasting.  A scaleable mapping from IP multicast   addresses to an ATM "group address" can address this problem.Crawley, et. al.             Informational                      [Page 9]

RFC 2382         Integrated Services and RSVP over ATM       August 19982.1.3.5 Label Switching   The MultiProtocol Label Switching (MPLS) working group is discussing   methods for optimizing the use of ATM and other switched networks for   IP by encapsulating the data with a header that is used by the   interior switches to achieve faster forwarding lookups.  [22]   discusses a framework for this work.  It is unclear how this work   will affect IntServ and RSVP over label switched networks but there   may be some interactions.2.1.4 QoS Routing   RSVP is explicitly not a routing protocol.  However, since it conveys   QoS information, it may prove to be a valuable input to a routing   protocol that can make path determinations based on QoS and network   load information.  In other words, instead of asking for just the IP   next hop for a given destination address, it might be worthwhile for   RSVP to provide information on the QoS needs of the flow if routing   has the ability to use this information in order to determine a   route.  Other forms of QoS routing have existed in the past such as   using the IP TOS and Precedence bits to select a path through the   network.  Some have discussed using these same bits to select one of   a set of parallel ATM VCs as a form of QoS routing.  ATM routing has   also considered the problem of QoS routing through the Private   Network-to-Network Interface (PNNI) [26] routing protocol for routing   ATM VCs on a path that can support their needs.  The work in this   area is just starting and there are numerous issues to consider.   [23], as part of the work of the QoSR working group frame the issues   for QoS Routing in the Internet.2.2 Reliance on Unicast and Multicast Routing   RSVP was designed to support both unicast and IP multicast   applications.  This means that RSVP needs to work closely with   multicast and unicast routing.  Unicast routing over ATM has been   addressed [10] and [11].  MARS [5] provides multicast address   resolution for IP over ATM networks, an important part of the   solution for multicast but still relies on multicast routing   protocols to connect multicast senders and receivers on different   subnets.2.3 Aggregation of Flows   Some of the scaling issues noted in previous sections can be   addressed by aggregating several RSVP flows over a single VC if the   destinations of the VC match for all the flows being aggregated.   However, this causes considerable complexity in the management of VCs   and in the scheduling of packets within each VC at the root point ofCrawley, et. al.             Informational                     [Page 10]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   the VC.  Note that the rescheduling of flows within a VC is not   possible in the switches in the core of the ATM network. Virtual   Paths (VPs) can be used for aggregating multiple VCs. This topic is   discussed in greater detail as it applies to multicast data   distribution insection 4.2.3.42.4 Mapping QoS Parameters   The mapping of QoS parameters from the IntServ models to the ATM   service classes is an important issue in making RSVP and IntServ work   over ATM.  [14] addresses these issues very completely for the   Controlled Load and Guaranteed Service models.  An additional issue   is that while some guidelines can be developed for mapping the   parameters of a given service model to the traffic descriptors of an   ATM traffic class, implementation variables, policy, and cost factors   can make strict mapping problematic.  So, a set of workable mappings   that can be applied to different network requirements and scenarios   is needed as long as the mappings can satisfy the needs of the   service model(s).2.5 Directly Connected ATM Hosts   It is obvious that the needs of hosts that are directly connected to   ATM networks must be considered for RSVP and IntServ over ATM.   Functionality for RSVP over ATM must not assume that an ATM host has   all the functionality of a router, but such things as MARS and NHRP   clients would be worthwhile features.  A host must manage VCs just   like any other ATM sender or receiver as described later insection4.2.6 Accounting and Policy Issues   Since RSVP and IntServ create classes of preferential service, some   form of administrative control and/or cost allocation is needed to   control access.  There are certain types of policies specific to ATM   and IP over ATM that need to be studied to determine how they   interoperate with the IP and IntServ policies being developed.   Typical IP policies would be that only certain users are allowed to   make reservations.  This policy would translate well to IP over ATM   due to the similarity to the mechanisms used for Call Admission   Control (CAC).   There may be a need for policies specific to IP over ATM.  For   example, since signalling costs in ATM are high relative to IP, an IP   over ATM specific policy might restrict the ability to change the   prevailing QoS in a VC.  If VCs are relatively scarce, there also   might be specific accounting costs in creating a new VC.  The work so   far has been preliminary, and much work remains to be done.  TheCrawley, et. al.             Informational                     [Page 11]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   policy mechanisms outlined in [12] and [13] provide the basic   mechanisms for implementing policies for RSVP and IntServ over any   media, not just ATM.3. Framework for IntServ and RSVP over ATM   Now that we have defined some of the issues for IntServ and RSVP over   ATM, we can formulate a framework for solutions.  The problem breaks   down to two very distinct areas; the mapping of IntServ models to ATM   service categories and QoS parameters and the operation of RSVP over   ATM.   Mapping IntServ models to ATM service categories and QoS parameters   is a matter of determining which categories can support the goals of   the service models and matching up the parameters and variables   between the IntServ description and the ATM description(s).  Since   ATM has such a wide variety of service categories and parameters,   more than one ATM service category should be able to support each of   the two IntServ models.  This will provide a good bit of flexibility   in configuration and deployment.  [14] examines this topic   completely.   The operation of RSVP over ATM requires careful management of VCs in   order to match the dynamics of the RSVP protocol.  VCs need to be   managed for both the RSVP QoS data and the RSVP signalling messages.   The remainder of this document will discuss several approaches to   managing VCs for RSVP and [15] and [16] discuss their application for   implementations in term of interoperability requirement and   implementation guidelines.4. RSVP VC Management   This section provides more detail on the issues related to the   management of SVCs for RSVP and IntServ.4.1 VC Initiation   As discussed insection 2.1.1.2, there is an apparent mismatch   between RSVP and ATM. Specifically, RSVP control is receiver oriented   and ATM control is sender oriented.  This initially may seem like a   major issue, but really is not.  While RSVP reservation (RESV)   requests are generated at the receiver, actual allocation of   resources takes place at the subnet sender. For data flows, this   means that subnet senders will establish all QoS VCs and the subnet   receiver must be able to accept incoming QoS VCs, as illustrated in   Figure 1.  These restrictions are consistent with RSVP version 1   processing rules and allow senders to use different flow to VC   mappings and even different QoS renegotiation techniques withoutCrawley, et. al.             Informational                     [Page 12]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   interoperability problems.   The use of the reverse path provided by point-to-point VCs by   receivers is for further study. There are two related issues. The   first is that use of the reverse path requires the VC initiator to   set appropriate reverse path QoS parameters. The second issue is that   reverse paths are not available with point-to-multipoint VCs, so   reverse paths could only be used to support unicast RSVP   reservations.4.2 Data VC Management   Any RSVP over ATM implementation must map RSVP and RSVP associated   data flows to ATM Virtual Circuits (VCs). LAN Emulation [17],   Classical IP [10] and, more recently, NHRP [4] discuss mapping IP   traffic onto ATM SVCs, but they only cover a single QoS class, i.e.,   best effort traffic. When QoS is introduced, VC mapping must be   revisited. For RSVP controlled QoS flows, one issue is VCs to use for   QoS data flows.   In the Classic IP over ATM and current NHRP models, a single point-   to-point VC is used for all traffic between two ATM attached hosts   (routers and end-stations).  It is likely that such a single VC will   not be adequate or optimal when supporting data flows with multiple   .bp QoS types. RSVP's basic purpose is to install support for flows   with multiple QoS types, so it is essential for any RSVP over ATM   solution to address VC usage for QoS data flows, as shown in Figure   1.   RSVP reservation styles must also be taken into account in any VC   usage strategy.   This section describes issues and methods for management of VCs   associated with QoS data flows. When establishing and maintaining   VCs, the subnet sender will need to deal with several complicating   factors including multiple QoS reservations, requests for QoS   changes, ATM short-cuts, and several multicast specific issues. The   multicast specific issues result from the nature of ATM connections.   The key multicast related issues are heterogeneity, data   distribution, receiver transitions, and end-point identification.4.2.1 Reservation to VC Mapping   There are various approaches available for mapping reservations on to   VCs.  A distinguishing attribute of all approaches is how   reservations are combined on to individual VCs.  When mapping   reservations on to VCs, individual VCs can be used to support a   single reservation, or reservation can be combined with others on toCrawley, et. al.             Informational                     [Page 13]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   "aggregate" VCs.  In the first case, each reservation will be   supported by one or more VCs.  Multicast reservation requests may   translate into the setup of multiple VCs as is described in more   detail insection 4.2.2.  Unicast reservation requests will always   translate into the setup of a single QoS VC.  In both cases, each VC   will only carry data associated with a single reservation.  The   greatest benefit if this approach is ease of implementation, but it   comes at the cost of increased (VC) setup time and the consumption of   greater number of VC and associated resources.   When multiple reservations are combined onto a single VC, it is   referred to as the "aggregation" model. With this model, large VCs   could be set up between IP routers and hosts in an ATM network. These   VCs could be managed much like IP Integrated Service (IIS) point-to-   point links (e.g. T-1, DS-3) are managed now.  Traffic from multiple   sources over multiple RSVP sessions might be multiplexed on the same   VC.  This approach has a number of advantages. First, there is   typically no signalling latency as VCs would be in existence when the   traffic started flowing, so no time is wasted in setting up VCs.   Second, the heterogeneity problem (section 4.2.2) in full over ATM   has been reduced to a solved problem. Finally, the dynamic QoS   problem (section 4.2.7) for ATM has also been reduced to a solved   problem.   The aggregation model can be used with point-to-point and point-to-   multipoint VCs.  The problem with the aggregation model is that the   choice of what QoS to use for the VCs may be difficult, without   knowledge of the likely reservation types and sizes but is made   easier since the VCs can be changed as needed.4.2.2 Unicast Data VC Management   Unicast data VC management is much simpler than multicast data VC   management but there are still some similar issues.  If one considers   unicast to be a devolved case of multicast, then implementing the   multicast solutions will cover unicast.  However, some may want to   consider unicast-only implementations.  In these situations, the   choice of using a single flow per VC or aggregation of flows onto a   single VC remains but the problem of heterogeneity discussed in the   following section is removed.4.2.3 Multicast Heterogeneity   As mentioned insection 2.1.3.1 and shown in figure 2, multicast   heterogeneity occurs when receivers request different qualities of   service within a single session.  This means that the amount of   requested resources differs on a per next hop basis. A related type   of heterogeneity occurs due to best-effort receivers.  In any IPCrawley, et. al.             Informational                     [Page 14]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   multicast group, it is possible that some receivers will request QoS   (via RSVP) and some receivers will not. In shared media networks,   like Ethernet, receivers that have not requested resources can   typically be given identical service to those that have without   complications.  This is not the case with ATM. In ATM networks, any   additional end-points of a VC must be explicitly added. There may be   costs associated with adding the best-effort receiver, and there   might not be adequate resources.  An RSVP over ATM solution will need   to support heterogeneous receivers even though ATM does not currently   provide such support directly.   RSVP heterogeneity is supported over ATM in the way RSVP reservations   are mapped into ATM VCs.  There are four alternative approaches this   mapping. There are multiple models for supporting RSVP heterogeneity   over ATM.Section 4.2.3.1 examines the multiple VCs per RSVP   reservation (or full heterogeneity) model where a single reservation   can be forwarded onto several VCs each with a different QoS.Section4.2.3.2 presents a limited heterogeneity model where exactly one QoS   VC is used along with a best effort VC.Section 4.2.3.3 examines the   VC per RSVP reservation (or homogeneous) model, where each RSVP   reservation is mapped to a single ATM VC.Section 4.2.3.4 describes   the aggregation model allowing aggregation of multiple RSVP   reservations into a single VC.4.2.3.1 Full Heterogeneity Model   RSVP supports heterogeneous QoS, meaning that different receivers of   the same multicast group can request a different QoS.  But   importantly, some receivers might have no reservation at all and want   to receive the traffic on a best effort service basis.  The IP model   allows receivers to join a multicast group at any time on a best   effort basis, and it is important that ATM as part of the Internet   continue to provide this service. We define the "full heterogeneity"   model as providing a separate VC for each distinct QoS for a   multicast session including best effort and one or more qualities of   service.   Note that while full heterogeneity gives users exactly what they   request, it requires more resources of the network than other   possible approaches. The exact amount of bandwidth used for duplicate   traffic depends on the network topology and group membership.4.2.3.2 Limited Heterogeneity Model   We define the "limited heterogeneity" model as the case where the   receivers of a multicast session are limited to use either best   effort service or a single alternate quality of service.  The   alternate QoS can be chosen either by higher level protocols or byCrawley, et. al.             Informational                     [Page 15]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   dynamic renegotiation of QoS as described below.   In order to support limited heterogeneity, each ATM edge device   participating in a session would need at most two VCs.  One VC would   be a point-to-multipoint best effort service VC and would serve all   best effort service IP destinations for this RSVP session.   The other VC would be a point to multipoint VC with QoS and would   serve all IP destinations for this RSVP session that have an RSVP   reservation established.   As with full heterogeneity, a disadvantage of the limited   heterogeneity scheme is that each packet will need to be duplicated   at the network layer and one copy sent into each of the 2 VCs.   Again, the exact amount of excess traffic will depend on the network   topology and group membership. If any of the existing QoS VC end-   points cannot upgrade to the new QoS, then the new reservation fails   though the resources exist for the new receiver.4.2.3.3 Homogeneous and Modified Homogeneous Models   We define the "homogeneous" model as the case where all receivers of   a multicast session use a single quality of service VC. Best-effort   receivers also use the single RSVP triggered QoS VC.  The single VC   can be a point-to-point or point-to-multipoint as appropriate. The   QoS VC is sized to provide the maximum resources requested by all   RSVP next- hops.   This model matches the way the current RSVP specification addresses   heterogeneous requests. The current processing rules and traffic   control interface describe a model where the largest requested   reservation for a specific outgoing interface is used in resource   allocation, and traffic is transmitted at the higher rate to all   next-hops. This approach would be the simplest method for RSVP over   ATM implementations.   While this approach is simple to implement, providing better than   best-effort service may actually be the opposite of what the user   desires.  There may be charges incurred or resources that are   wrongfully allocated.  There are two specific problems. The first   problem is that a user making a small or no reservation would share a   QoS VC resources without making (and perhaps paying for) an RSVP   reservation. The second problem is that a receiver may not receive   any data.  This may occur when there is insufficient resources to add   a receiver.  The rejected user would not be added to the single VC   and it would not even receive traffic on a best effort basis.Crawley, et. al.             Informational                     [Page 16]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   Not sending data traffic to best-effort receivers because of another   receiver's RSVP request is clearly unacceptable.  The previously   described limited heterogeneous model ensures that data is always   sent to both QoS and best-effort receivers, but it does so by   requiring replication of data at the sender in all cases.  It is   possible to extend the homogeneous model to both ensure that data is   always sent to best-effort receivers and also to avoid replication in   the normal case.  This extension is to add special handling for the   case where a best- effort receiver cannot be added to the QoS VC.  In   this case, a best effort VC can be established to any receivers that   could not be added to the QoS VC. Only in this special error case   would senders be required to replicate data.  We define this approach   as the "modified homogeneous" model.4.2.3.4 Aggregation   The last scheme is the multiple RSVP reservations per VC (or   aggregation) model. With this model, large VCs could be set up   between IP routers and hosts in an ATM network. These VCs could be   managed much like IP Integrated Service (IIS) point-to-point links   (e.g. T-1, DS-3) are managed now. Traffic from multiple sources over   multiple RSVP sessions might be multiplexed on the same VC. This   approach has a number of advantages. First, there is typically no   signalling latency as VCs would be in existence when the traffic   started flowing, so no time is wasted in setting up VCs.   Second,   the heterogeneity problem in full over ATM has been reduced to a   solved problem. Finally, the dynamic QoS problem for ATM has also   been reduced to a solved problem.  This approach can be used with   point-to-point and point-to-multipoint VCs. The problem with the   aggregation approach is that the choice of what QoS to use for which   of the VCs is difficult, but is made easier if the VCs can be changed   as needed.4.2.4 Multicast End-Point Identification   Implementations must be able to identify ATM end-points participating   in an IP multicast group.  The ATM end-points will be IP multicast   receivers and/or next-hops.  Both QoS and best-effort end-points must   be identified.  RSVP next-hop information will provide QoS end-   points, but not best-effort end-points. Another issue is identifying   end-points of multicast traffic handled by non-RSVP capable next-   hops. In this case a PATH message travels through a non-RSVP egress   router on the way to the next hop RSVP node.  When the next hop RSVP   node sends a RESV message it may arrive at the source over a   different route than what the data is using. The source will get the   RESV message, but will not know which egress router needs the QoS.   For unicast sessions, there is no problem since the ATM end-point   will be the IP next-hop router.  Unfortunately, multicast routing mayCrawley, et. al.             Informational                     [Page 17]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   not be able to uniquely identify the IP next-hop router.  So it is   possible that a multicast end-point can not be identified.   In the most common case, MARS will be used to identify all end-points   of a multicast group.  In the router to router case, a multicast   routing protocol may provide all next-hops for a particular multicast   group.  In either case, RSVP over ATM implementations must obtain a   full list of end-points, both QoS and non-QoS, using the appropriate   mechanisms.  The full list can be compared against the RSVP   identified end-points to determine the list of best-effort receivers.   There is no straightforward solution to uniquely identifying end-   points of multicast traffic handled by non-RSVP next hops.  The   preferred solution is to use multicast routing protocols that support   unique end-point identification.  In cases where such routing   protocols are unavailable, all IP routers that will be used to   support RSVP over ATM should support RSVP.  To ensure proper   behavior, implementations should, by default, only establish RSVP-   initiated VCs to RSVP capable end-points.4.2.5 Multicast Data Distribution   Two models are planned for IP multicast data distribution over ATM.   In one model, senders establish point-to-multipoint VCs to all ATM   attached destinations, and data is then sent over these VCs.  This   model is often called "multicast mesh" or "VC mesh" mode   distribution.  In the second model, senders send data over point-to-   point VCs to a central point and the central point relays the data   onto point-to-multipoint VCs that have been established to all   receivers of the IP multicast group.  This model is often referred to   as "multicast server" mode distribution. RSVP over ATM solutions must   ensure that IP multicast data is distributed with appropriate QoS.   In the Classical IP context, multicast server support is provided via   MARS [5].  MARS does not currently provide a way to communicate QoS   requirements to a MARS multicast server.  Therefore, RSVP over ATM   implementations must, by default, support "mesh-mode" distribution   for RSVP controlled multicast flows.  When using multicast servers   that do not support QoS requests, a sender must set the service, not   global, break bit(s).4.2.6 Receiver Transitions   When setting up a point-to-multipoint VCs for multicast RSVP   sessions, there will be a time when some receivers have been added to   a QoS VC and some have not.  During such transition times it is   possible to start sending data on the newly established VC.  The   issue is when to start send data on the new VC.  If data is sent both   on the new VC and the old VC, then data will be delivered with properCrawley, et. al.             Informational                     [Page 18]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   QoS to some receivers and with the old QoS to all receivers.  This   means the QoS receivers can get duplicate data.  If data is sent just   on the new QoS VC, the receivers that have not yet been added will   lose information.  So, the issue comes down to whether to send to   both the old and new VCs, or to send to just one of the VCs.  In one   case duplicate information will be received, in the other some   information may not be received.   This issue needs to be considered for three cases:   - When establishing the first QoS VC   - When establishing a VC to support a QoS change   - When adding a new end-point to an already established QoS VC   The first two cases are very similar.  It both, it is possible to   send data on the partially completed new VC, and the issue of   duplicate versus lost information is the same. The last case is when   an end-point must be added to an existing QoS VC.  In this case the   end-point must be both added to the QoS VC and dropped from a best-   effort VC.  The issue is which to do first.  If the add is first   requested, then the end-point may get duplicate information.  If the   drop is requested first, then the end-point may loose information.   In order to ensure predictable behavior and delivery of data to all   receivers, data can only be sent on a new VCs once all parties have   been added.  This will ensure that all data is only delivered once to   all receivers.  This approach does not quite apply for the last case.   In the last case, the add operation should be completed first, then   the drop operation.  This means that receivers must be prepared to   receive some duplicate packets at times of QoS setup.4.2.7 Dynamic QoS   RSVP provides dynamic quality of service (QoS) in that the resources   that are requested may change at any time. There are several common   reasons for a change of reservation QoS.   1. An existing receiver can request a new larger (or smaller) QoS.   2. A sender may change its traffic specification (TSpec), which can      trigger a change in the reservation requests of the receivers.   3. A new sender can start sending to a multicast group with a larger      traffic specification than existing senders, triggering larger      reservations.   4. A new receiver can make a reservation that is larger than existing      reservations.Crawley, et. al.             Informational                     [Page 19]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   If the limited heterogeneity model is being used and the merge node   for the larger reservation is an ATM edge device, a new larger   reservation must be set up across the ATM network. Since ATM service,   as currently defined in UNI 3.x and UNI 4.0, does not allow   renegotiating the QoS of a VC, dynamically changing the reservation   means creating a new VC with the new QoS, and tearing down an   established VC. Tearing down a VC and setting up a new VC in ATM are   complex operations that involve a non-trivial amount of processing   time, and may have a substantial latency.  There are several options   for dealing with this mismatch in service.  A specific approach will   need to be a part of any RSVP over ATM solution.   The default method for supporting changes in RSVP reservations is to   attempt to replace an existing VC with a new appropriately sized VC.   During setup of the replacement VC, the old VC must be left in place   unmodified. The old VC is left unmodified to minimize interruption of   QoS data delivery.  Once the replacement VC is established, data   transmission is shifted to the new VC, and the old VC is then closed.   If setup of the replacement VC fails, then the old QoS VC should   continue to be used. When the new reservation is greater than the old   reservation, the reservation request should be answered with an   error.  When the new reservation is less than the old reservation,   the request should be treated as if the modification was successful.   While leaving the larger allocation in place is suboptimal, it   maximizes delivery of service to the user. Implementations should   retry replacing the too large VC after some appropriate elapsed time.   One additional issue is that only one QoS change can be processed at   one time per reservation. If the (RSVP) requested QoS is changed   while the first replacement VC is still being setup, then the   replacement VC is released and the whole VC replacement process is   restarted. To limit the number of changes and to avoid excessive   signalling load, implementations may limit the number of changes that   will be processed in a given period.  One implementation approach   would have each ATM edge device configured with a time parameter T   (which can change over time) that gives the minimum amount of time   the edge device will wait between successive changes of the QoS of a   particular VC.  Thus if the QoS of a VC is changed at time t, all   messages that would change the QoS of that VC that arrive before time   t+T would be queued. If several messages changing the QoS of a VC   arrive during the interval, redundant messages can be discarded. At   time t+T, the remaining change(s) of QoS, if any, can be executed.   This timer approach would apply more generally to any network   structure, and might be worthwhile to incorporate into RSVP.Crawley, et. al.             Informational                     [Page 20]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   The sequence of events for a single VC would be   - Wait if timer is active   - Establish VC with new QoS   - Remap data traffic to new VC   - Tear down old VC   - Activate timer   There is an interesting interaction between heterogeneous   reservations and dynamic QoS. In the case where a RESV message is   received from a new next-hop and the requested resources are larger   than any existing reservation, both dynamic QoS and heterogeneity   need to be addressed. A key issue is whether to first add the new   next-hop or to change to the new QoS. This is a fairly straight   forward special case. Since the older, smaller reservation does not   support the new next-hop, the dynamic QoS process should be initiated   first. Since the new QoS is only needed by the new next-hop, it   should be the first end-point of the new VC.  This way signalling is   minimized when the setup to the new next-hop fails.4.2.8 Short-Cuts   Short-cuts [4] allow ATM attached routers and hosts to directly   establish point-to-point VCs across LIS boundaries, i.e., the VC   end-points are on different IP subnets.  The ability for short-cuts   and RSVP to interoperate has been raised as a general question.  An   area of concern is the ability to handle asymmetric short-cuts.   Specifically how RSVP can handle the case where a downstream short-   cut may not have a matching upstream short-cut.  In this case, PATH   and RESV messages following different paths.   Examination of RSVP shows that the protocol already includes   mechanisms that will support short-cuts.  The mechanism is the same   one used to support RESV messages arriving at the wrong router and   the wrong interface.  The key aspect of this mechanism is RSVP only   processing messages that arrive at the proper interface and RSVP   forwarding of messages that arrive on the wrong interface.  The   proper interface is indicated in the NHOP object of the message.  So,   existing RSVP mechanisms will support asymmetric short-cuts. The   short-cut model of VC establishment still poses several issues when   running with RSVP. The major issues are dealing with established   best-effort short-cuts, when to establish short-cuts, and QoS only   short-cuts. These issues will need to be addressed by RSVP   implementations.   The key issue to be addressed by any RSVP over ATM solution is when   to establish a short-cut for a QoS data flow. The default behavior is   to simply follow best-effort traffic. When a short-cut has beenCrawley, et. al.             Informational                     [Page 21]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   established for best-effort traffic to a destination or next-hop,   that same end-point should be used when setting up RSVP triggered VCs   for QoS traffic to the same destination or next-hop. This will happen   naturally when PATH messages are forwarded over the best-effort   short-cut.  Note that in this approach when best-effort short-cuts   are never established, RSVP triggered QoS short-cuts will also never   be established.  More study is expected in this area.4.2.9 VC Teardown   RSVP can identify from either explicit messages or timeouts when a   data VC is no longer needed.  Therefore, data VCs set up to support   RSVP controlled flows should only be released at the direction of   RSVP. VCs must not be timed out due to inactivity by either the VC   initiator or the VC receiver.   This conflicts with VCs timing out as   described inRFC 1755 [11], section 3.4 on VC Teardown.RFC 1755   recommends tearing down a VC that is inactive for a certain length of   time. Twenty minutes is recommended. This timeout is typically   implemented at both the VC initiator and the VC receiver.   Although,section 3.1 of the update toRFC 1755 [11] states that inactivity   timers must not be used at the VC receiver.   When this timeout occurs for an RSVP initiated VC, a valid VC with   QoS will be torn down unexpectedly.  While this behavior is   acceptable for best-effort traffic, it is important that RSVP   controlled VCs not be torn down.  If there is no choice about the VC   being torn down, the RSVP daemon must be notified, so a reservation   failure message can be sent.   For VCs initiated at the request of RSVP, the configurable inactivity   timer mentioned in [11] must be set to "infinite".  Setting the   inactivity timer value at the VC initiator should not be problematic   since the proper value can be relayed internally at the originator.   Setting the inactivity timer at the VC receiver is more difficult,   and would require some mechanism to signal that an incoming VC was   RSVP initiated.  To avoid this complexity and to conform to [11]   implementations must not use an inactivity timer to clear received   connections.4.3 RSVP Control Management   One last important issue is providing a data path for the RSVP   messages themselves.  There are two main types of messages in RSVP,   PATH and RESV. PATH messages are sent to unicast or multicast   addresses, while RESV messages are sent only to unicast addresses.   Other RSVP messages are handled similar to either PATH or RESV,   although this might be more complicated for RERR messages.  So ATM   VCs used for RSVP signalling messages need to provide both unicastCrawley, et. al.             Informational                     [Page 22]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   and multicast functionality.  There are several different approaches   for how to assign VCs to use for RSVP signalling messages.   The main approaches are:      - use same VC as data      - single VC per session      - single point-to-multipoint VC multiplexed among sessions      - multiple point-to-point VCs multiplexed among sessions   There are several different issues that affect the choice of how to   assign VCs for RSVP signalling. One issue is the number of additional   VCs needed for RSVP signalling. Related to this issue is the degree   of multiplexing on the RSVP VCs. In general more multiplexing means   fewer VCs. An additional issue is the latency in dynamically setting   up new RSVP signalling VCs. A final issue is complexity of   implementation. The remainder of this section discusses the issues   and tradeoffs among these different approaches and suggests   guidelines for when to use which alternative.4.3.1 Mixed data and control traffic   In this scheme RSVP signalling messages are sent on the same VCs as   is the data traffic. The main advantage of this scheme is that no   additional VCs are needed beyond what is needed for the data traffic.   An additional advantage is that there is no ATM signalling latency   for PATH messages (which follow the same routing as the data   messages).  However there can be a major problem when data traffic on   a VC is nonconforming. With nonconforming traffic, RSVP signalling   messages may be dropped. While RSVP is resilient to a moderate level   of dropped messages, excessive drops would lead to repeated tearing   down and re-establishing of QoS VCs, a very undesirable behavior for   ATM. Due to these problems, this may not be a good choice for   providing RSVP signalling messages, even though the number of VCs   needed for this scheme is minimized. One variation of this scheme is   to use the best effort data path for signalling traffic. In this   scheme, there is no issue with nonconforming traffic, but there is an   issue with congestion in the ATM network. RSVP provides some   resiliency to message loss due to congestion, but RSVP control   messages should be offered a preferred class of service. A related   variation of this scheme that is hopeful but requires further study   is to have a packet scheduling algorithm (before entering the ATM   network) that gives priority to the RSVP signalling traffic. This can   be difficult to do at the IP layer.Crawley, et. al.             Informational                     [Page 23]

RFC 2382         Integrated Services and RSVP over ATM       August 19984.3.1.1 Single RSVP VC per RSVP Reservation   In this scheme, there is a parallel RSVP signalling VC for each RSVP   reservation. This scheme results in twice the number of VCs, but   means that RSVP signalling messages have the advantage of a separate   VC.  This separate VC means that RSVP signalling messages have their   own traffic contract and compliant signalling messages are not   subject to dropping due to other noncompliant traffic (such as can   happen with the scheme insection 4.3.1). The advantage of this   scheme is its simplicity - whenever a data VC is created, a separate   RSVP signalling VC is created.  The disadvantage of the extra VC is   that extra ATM signalling needs to be done. Additionally, this scheme   requires twice the minimum number of VCs and also additional latency,   but is quite simple.4.3.1.2 Multiplexed point-to-multipoint RSVP VCs   In this scheme, there is a single point-to-multipoint RSVP signalling   VC for each unique ingress router and unique set of egress routers.   This scheme allows multiplexing of RSVP signalling traffic that   shares the same ingress router and the same egress routers.  This can   save on the number of VCs, by multiplexing, but there are problems   when the destinations of the multiplexed point-to-multipoint VCs are   changing.  Several alternatives exist in these cases, that have   applicability in different situations. First, when the egress routers   change, the ingress router can check if it already has a point-to-   multipoint RSVP signalling VC for the new list of egress routers. If   the RSVP signalling VC already exists, then the RSVP signalling   traffic can be switched to this existing VC. If no such VC exists,   one approach would be to create a new VC with the new list of egress   routers. Other approaches include modifying the existing VC to add an   egress router or using a separate new VC for the new egress routers.   When a destination drops out of a group, an alternative would be to   keep sending to the existing VC even though some traffic is wasted.   The number of VCs used in this scheme is a function of traffic   patterns across the ATM network, but is always less than the number   used with the Single RSVP VC per data VC. In addition, existing best   effort data VCs could be used for RSVP signalling. Reusing best   effort VCs saves on the number of VCs at the cost of higher   probability of RSVP signalling packet loss.  One possible place where   this scheme will work well is in the core of the network where there   is the most opportunity to take advantage of the savings due to   multiplexing.  The exact savings depend on the patterns of traffic   and the topology of the ATM network.Crawley, et. al.             Informational                     [Page 24]

RFC 2382         Integrated Services and RSVP over ATM       August 19984.3.1.3 Multiplexed point-to-point RSVP VCs   In this scheme, multiple point-to-point RSVP signalling VCs are used   for a single point-to-multipoint data VC.  This scheme allows   multiplexing of RSVP signalling traffic but requires the same traffic   to be sent on each of several VCs. This scheme is quite flexible and   allows a large amount of multiplexing.   Since point-to-point VCs can set up a reverse channel at the same   time as setting up the forward channel, this scheme could save   substantially on signalling cost.  In addition, signalling traffic   could share existing best effort VCs.  Sharing existing best effort   VCs reduces the total number of VCs needed, but might cause   signalling traffic drops if there is congestion in the ATM network.   This point-to-point scheme would work well in the core of the network   where there is much opportunity for multiplexing. Also in the core of   the network, RSVP VCs can stay permanently established either as   Permanent Virtual Circuits (PVCs) or  as long lived Switched Virtual   Circuits (SVCs). The number of VCs in this scheme will depend on   traffic patterns, but in the core of a network would be approximately   n(n-1)/2 where n is the number of IP nodes in the network.  In the   core of the network, this will typically be small compared to the   total number of VCs.4.3.2 QoS for RSVP VCs   There is an issue of what QoS, if any, to assign to the RSVP   signalling VCs. For other RSVP VC schemes, a QoS (possibly best   effort) will be needed.  What QoS to use partially depends on the   expected level of multiplexing that is being done on the VCs, and the   expected reliability of best effort VCs. Since RSVP signalling is   infrequent (typically every 30 seconds), only a relatively small QoS   should be needed. This is important since using a larger QoS risks   the VC setup being rejected for lack of resources. Falling back to   best effort when a QoS call is rejected is possible, but if the ATM   net is congested, there will likely be problems with RSVP packet loss   on the best effort VC also. Additional experimentation is needed in   this area.5. Encapsulation   Since RSVP is a signalling protocol used to control flows of IP data   packets, encapsulation for both RSVP packets and associated IP data   packets must be defined. The methods for transmitting IP packets over   ATM (Classical IP over ATM[10], LANE[17], and MPOA[18]) are all based   on the encapsulations defined inRFC1483 [19].RFC1483 specifies two   encapsulations, LLC Encapsulation and VC-based multiplexing.  The   former allows multiple protocols to be encapsulated over the same VCCrawley, et. al.             Informational                     [Page 25]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   and the latter requires different VCs for different protocols.   For the purposes of RSVP over ATM, any encapsulation can be used as   long as the VCs are managed in accordance to the methods outlined inSection 4.  Obviously, running multiple protocol data streams over   the same VC with LLC encapsulation can cause the same problems as   running multiple flows over the same VC.   While none of the transmission methods directly address the issue of   QoS,RFC1755 [11] does suggest some common values for VC setup for   best-effort traffic.  [14] discusses the relationship of theRFC1755   setup parameters and those needed to support IntServ flows in greater   detail.6. Security Considerations   The same considerations stated in [1] and [11] apply to this   document.  There are no additional security issues raised in this   document.7. References   [1] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. Jamin,       "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional       Specification",RFC 2209, September 1997.   [2] Borden, M., Crawley, E., Davie, B., and S. Batsell, "Integration       of Realtime Services in an IP-ATM Network Architecture",RFC1821, August 1995.   [3] Cole, R., Shur, D., and C. Villamizar, "IP over ATM: A Framework       Document",RFC 1932, April 1996.   [4] Luciani, J., Katz, D., Piscitello, D., Cole, B., and N.       Doraswamy, "NBMA Next Hop Resolution Protocol (NHRP)",RFC 2332,       April 1998.   [5] Armitage, G., "Support for Multicast over UNI 3.0/3.1 based ATM       Networks",RFC 2022, November 1996.   [6] Shenker, S., and C. Partridge, "Specification of Guaranteed       Quality of Service",RFC 2212, September 1997.   [7] Wroclawski, J., "Specification of the Controlled-Load Network       Element Service",RFC 2211, September 1997.   [8] ATM Forum. ATM User-Network Interface Specification Version 3.0.       Prentice Hall, September 1993.Crawley, et. al.             Informational                     [Page 26]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   [9] ATM Forum. ATM User Network Interface (UNI) Specification Version       3.1. Prentice Hall, June 1995.   [10] Laubach, M., "Classical IP and ARP over ATM",RFC 2225, April        1998.   [11] Perez, M., Mankin, A., Hoffman, E., Grossman, G., and A. Malis,        "ATM Signalling Support for IP over ATM",RFC 1755, February        1995.   [12] Herzog, S.,"RSVP Extensions for Policy Control", Work in        Progress.   [13] Herzog, S., "Local Policy Modules (LPM): Policy Control for        RSVP", Work in Progress.   [14] Borden, M., and M. Garrett, "Interoperation of Controlled-Load        and Guaranteed Service with ATM",RFC 2381, August 1998.   [15] Berger, L., "RSVP over ATM Implementation Requirements",RFC2380, August 1998.   [16] Berger, L., "RSVP over ATM Implementation Guidelines",RFC 2379,        August 1998.   [17] ATM Forum Technical Committee. LAN Emulation over ATM, Version        1.0 Specification, af-lane-0021.000, January 1995.   [18] ATM Forum Technical Committee. Baseline Text for MPOA, af-95-        0824r9, September 1996.   [19] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaptation        Layer 5",RFC 1483, July 1993.   [20] ATM Forum Technical Committee. LAN Emulation over ATM Version 2        - LUNI Specification, December 1996.   [21] ATM Forum Technical Committee. Traffic Management Specification        v4.0, af-tm-0056.000, April 1996.   [22] Callon, R., et al., "A Framework for Multiprotocol Label        Switching, Work in Progress.   [23] Rajagopalan, B., Nair, R., Sandick, H., and E. Crawley, "A        Framework for QoS-based Routing in the Internet",RFC 2386,        August 1998.Crawley, et. al.             Informational                     [Page 27]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   [24] ITU-T. Digital Subscriber Signaling System No. 2-Connection        modification: Peak cell rate modification by the connection        owner, ITU-T Recommendation Q.2963.1, July 1996.   [25] ITU-T. Digital Subscriber Signaling System No. 2-Connection        characteristics negotiation during call/connection establishment        phase, ITU-T Recommendation Q.2962, July 1996.   [26] ATM Forum Technical Committee. Private Network-Network Interface        Specification v1.0 (PNNI), March 1996.8. Authors' Addresses   Eric S. Crawley   Argon Networks   25 Porter Road   Littleton, Ma 01460   Phone: +1 978 486-0665   EMail: esc@argon.com   Lou Berger   FORE Systems   6905 Rockledge Drive   Suite 800   Bethesda, MD 20817   Phone: +1 301 571-2534   EMail: lberger@fore.com   Steven Berson   USC Information Sciences Institute   4676 Admiralty Way   Marina del Rey, CA 90292   Phone: +1 310 822-1511   EMail: berson@isi.edu   Fred Baker   Cisco Systems   519 Lado Drive   Santa Barbara, California 93111   Phone: +1 805 681-0115   EMail: fred@cisco.comCrawley, et. al.             Informational                     [Page 28]

RFC 2382         Integrated Services and RSVP over ATM       August 1998   Marty Borden   Bay Networks   125 Nagog Park   Acton, MA 01720   Phone: +1 978 266-1011   EMail: mborden@baynetworks.com   John J. Krawczyk   ArrowPoint Communications   235 Littleton Road   Westford, Massachusetts 01886   Phone: +1 978 692-5875   EMail: jj@arrowpoint.comCrawley, et. al.             Informational                     [Page 29]

RFC 2382         Integrated Services and RSVP over ATM       August 19989.  Full Copyright Statement   Copyright (C) The Internet Society (1998).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Crawley, et. al.             Informational                     [Page 30]