rfc2814.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                        R. Yavatkar
Request for Comments: 2814                                         Intel
Category: Standards Track                                     D. Hoffman
                                                               Teledesic
                                                               Y. Bernet
                                                               Microsoft
                                                                F. Baker
                                                                   Cisco
                                                                M. Speer
                                                        Sun Microsystems
                                                                May 2000


                    SBM (Subnet Bandwidth Manager):
A Protocol for RSVP-based Admission Control over IEEE 802-style networks

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   This document describes a signaling method and protocol for RSVP-
   based admission control over IEEE 802-style LANs.  The protocol is
   designed to work both with the current generation of IEEE 802 LANs as
   well as with the recent work completed by the IEEE 802.1 committee.

1. Introduction

   New extensions to the Internet architecture and service models have
   been defined for an integrated services Internet [RFC-1633, RFC-2205,
   RFC-2210] so that applications can request specific qualities or
   levels of service from an internetwork in addition to the current IP
   best-effort service.  These extensions include RSVP, a resource
   reservation setup protocol, and definition of new service classes to
   be supported by Integrated Services routers.  RSVP and service class
   definitions are largely independent of the underlying networking
   technologies and it is necessary to define the mapping of RSVP and
   Integrated Services specifications onto specific subnetwork
   technologies.  For example, a definition of service mappings and



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   reservation setup protocols is needed for specific link-layer
   technologies such as shared and switched IEEE-802-style LAN
   technologies.

   This document defines SBM, a signaling protocol for RSVP-based
   admission control over IEEE 802-style networks.  SBM provides a
   method for mapping an internet-level setup protocol such as RSVP onto
   IEEE 802 style networks.  In particular, it describes the operation
   of RSVP-enabled hosts/routers and link layer devices (switches,
   bridges) to support reservation of LAN resources for RSVP-enabled
   data flows.  A framework for providing Integrated Services over
   shared and switched IEEE-802-style LAN technologies and a definition
   of service mappings have been described in separate documents [RFC-
   FRAME, RFC-MAP].

2. Goals and Assumptions

   The SBM (Subnet Bandwidth Manager) protocol and its use for admission
   control and bandwidth management in IEEE 802 level-2 networks is
   based on the following architectural goals and assumptions:

      I. Even though the current trend is towards increased use of
      switched LAN topologies consisting of newer switches that support
      the priority queuing mechanisms specified by IEEE 802.1p, we
      assume that the LAN technologies will continue to be a mix of
      legacy shared/ switched LAN segments and newer switched segments
      based on IEEE 802.1p specification.  Therefore, we specify a
      signaling protocol for managing bandwidth over both legacy and
      newer LAN topologies and that takes advantage of the additional
      functionality (such as an explicit support for different traffic
      classes or integrated service classes) as it becomes available in
      the new generation of switches, hubs, or bridges.  As a result,
      the SBM protocol would allow for a range of LAN bandwidth
      management solutions that vary from one that exercises purely
      administrative control (over the amount of bandwidth consumed by
      RSVP-enabled traffic flows) to one that requires cooperation (and
      enforcement) from all the end-systems or switches in a IEEE 802
      LAN.

      II. This document specifies only a signaling method and protocol
      for LAN-based admission control over RSVP flows.  We do not define
      here any traffic control mechanisms for the link layer; the
      protocol is designed to use any such mechanisms defined by IEEE
      802.  In addition, we assume that the Layer 3 end-systems (e.g., a
      host or a router) will exercise traffic control by policing
      Integrated Services traffic flows to ensure that each flow stays
      within its traffic specifications stipulated in an earlier
      reservation request submitted for admission control.  This then



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      allows a system using SBM admission control combined with per flow
      shaping at end systems and IEEE-defined traffic control at link
      layer to realize some approximation of Controlled Load (and even
      Guaranteed) services over IEEE 802-style LANs.

      III. In the absence of any link-layer traffic control or priority
      queuing mechanisms in the underlying LAN (such as a shared LAN
      segment), the SBM-based admission control mechanism only limits
      the total amount of traffic load imposed by RSVP-enabled flows on
      a shared LAN. In such an environment, no traffic flow separation
      mechanism exists to protect the RSVP-enabled flows from the best-
      effort traffic on the same shared media and that raises the
      question of the utility of such a mechanism outside a topology
      consisting only of 802.1p-compliant switches.  However, we assume
      that the SBM-based admission control mechanism will still serve a
      useful purpose in a legacy, shared LAN topology for two reasons.
      First, assuming that all the nodes that generate Integrated
      Services traffic flows utilize the SBM-based admission control
      procedure to request reservation of resources before sending any
      traffic, the mechanism will restrict the total amount of traffic
      generated by Integrated Services flows within the bounds desired
      by a LAN administrator (see discussion of the NonResvSendLimit
      parameter in Appendix C).  Second, the best-effort traffic
      generated by the TCP/IP-based traffic sources is generally rate
      adaptive (using a TCP-style "slow start" congestion avoidance
      mechanism or a feedback-based rate adaptation mechanism used by
      audio/video streams based on RTP/RTCP protocols) and adapts to
      stay within the available network bandwidth.  Thus, the
      combination of admission control and rate adaptation should avoid
      persistent traffic congestion.  This does not, however, guarantee
      that non-Integrated-Services traffic will not interfere with the
      Integrated Services traffic in the absence of traffic control
      support in the underlying LAN infrastructure.

3. Organization of the rest of this document

   The rest of this document provides a detailed description of the
   SBM-based admission control procedure(s) for IEEE 802 LAN
   technologies. The document is organized as follows:

   *  Section 4 first defines the various terms used in the document and
      then provides an overview of the admission control procedure with
      an example of its application to a sample network.

   *  Section 5 describes the rules for processing and forwarding PATH
      (and PATH_TEAR) messages at DSBMs (Designated Subnet Bandwidth
      Managers), SBMs, and DSBM clients.




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   *  Section 6 addresses the inter-operability issues when a DSBM may
      operate in the absence of RSVP signaling at Layer 3 or when
      another signaling protocol (such as SNMP) is used to reserve
      resources on a LAN segment.

   *  Appendix A describes the details of the DSBM election algorithm
      used for electing a designated SBM on a LAN segment when more than
      one SBM is present.  It also describes how DSBM clients discover
      the presence of a DSBM on a managed segment.

   *  Appendix B specifies the formats of SBM-specific messages used and
      the formats of new RSVP objects needed for the SBM operation.

   *  Appendix C describes usage of the DSBM to distribute configuration
      information to senders on a managed segment.

4. Overview

4.1. Definitions

   -  Link Layer or Layer 2 or L2: We refer to data-link layer
      technologies such as IEEE 802.3/Ethernet as L2 or layer 2.

   -  Link Layer Domain or Layer 2 domain or L2 domain: a set of nodes
      and links interconnected without passing through a L3 forwarding
      function. One or more IP subnets can be overlaid on a L2 domain.

   -  Layer 2 or L2 devices: We refer to devices that only implement
      Layer 2 functionality as Layer 2 or L2 devices. These include
      802.1D bridges or switches.

   -  Internetwork Layer or Layer 3 or L3: Layer 3 of the ISO 7 layer
      model. This document is primarily concerned with networks that use
      the Internet Protocol (IP) at this layer.

   -  Layer 3 Device or L3 Device or End-Station: these include hosts
      and routers that use L3 and higher layer protocols or application
      programs that need to make resource reservations.

   -  Segment: A L2 physical segment that is shared by one or more
      senders. Examples of segments include (a) a shared Ethernet or
      Token-Ring wire resolving contention for media access using CSMA
      or token passing ("shared L2 segment"), (b) a half duplex link
      between two stations or switches, (c) one direction of a switched
      full-duplex link.






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   -  Managed segment: A managed segment is a segment with a DSBM
      present and responsible for exercising admission control over
      requests for resource reservation. A managed segment includes
      those interconnected parts of a shared LAN that are not separated
      by DSBMs.

   -  Traffic Class: An aggregation of data flows which are given
      similar service within a switched network.

   -  User_priority: User_priority is a value associated with the
      transmission and reception of all frames in the IEEE 802 service
      model: it is supplied by the sender that is using the MAC service.
      It is provided along with the data to a receiver using the MAC
      service. It may or may not be actually carried over the network:
      Token-Ring/802.5 carries this value (encoded in its FC octet),
      basic Ethernet/802.3 does not, 802.12 may or may not depending on
      the frame format in use. 802.1p defines a consistent way to carry
      this value over the bridged network on Ethernet, Token Ring,
      Demand-Priority, FDDI or other MAC-layer media using an extended
      frame format. The usage of user_priority is fully described in
      section 2.5 of 802.1D [IEEE8021D] and 802.1p [IEEE8021P] "Support
      of the Internal Layer Service by Specific MAC Procedures".

   -  Subnet: used in this memo to indicate a group of L3 devices
      sharing a common L3 network address prefix along with the set of
      segments making up the L2 domain in which they are located.

   -  Bridge/Switch: a layer 2 forwarding device as defined by IEEE
      802.1D. The terms bridge and switch are used synonymously in this
      document.

   -  DSBM: Designated SBM (DSBM) is a protocol entity that resides in a
      L2 or L3 device and manages resources on a L2 segment. At most one
      DSBM exists for each L2 segment.

   -  SBM: the SBM is a protocol entity that resides in a L2 or L3
      device and is capable of managing resources on a segment. However,
      only a DSBM manages the resources for a managed segment. When more
      than one SBM exists on a segment, one of the SBMs is elected to be
      the DSBM.

   -  Extended segment: An extended segment includes those parts of a
      network which are members of the same IP subnet and therefore are
      not separated by any layer 3 devices. Several managed segments,
      interconnected by layer 2 devices, constitute an extended segment.