rfc2475.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                                        S. Blake
Request for Comments: 2475            Torrent Networking Technologies
Category: Informational                                      D. Black
                                                      EMC Corporation
                                                           M. Carlson
                                                     Sun Microsystems
                                                            E. Davies
                                                            Nortel UK
                                                              Z. Wang
                                        Bell Labs Lucent Technologies
                                                             W. Weiss
                                                  Lucent Technologies
                                                        December 1998


              An Architecture for Differentiated Services

Status 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 defines an architecture for implementing scalable
   service differentiation in the Internet.  This architecture achieves
   scalability by aggregating traffic classification state which is
   conveyed by means of IP-layer packet marking using the DS field
   [DSFIELD].  Packets are classified and marked to receive a particular
   per-hop forwarding behavior on nodes along their path.  Sophisticated
   classification, marking, policing, and shaping operations need only
   be implemented at network boundaries or hosts.  Network resources are
   allocated to traffic streams by service provisioning policies which
   govern how traffic is marked and conditioned upon entry to a
   differentiated services-capable network, and how that traffic is
   forwarded within that network.  A wide variety of services can be
   implemented on top of these building blocks.









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Table of Contents

   1.  Introduction .................................................  2
     1.1  Overview  .................................................  2
     1.2  Terminology ...............................................  4
     1.3  Requirements ..............................................  8
     1.4  Comparisons with Other Approaches .........................  9
   2.  Differentiated Services Architectural Model .................. 12
     2.1  Differentiated Services Domain ............................ 12
       2.1.1  DS Boundary Nodes and Interior Nodes .................. 12
       2.1.2  DS Ingress Node and Egress Node ....................... 13
     2.2  Differentiated Services Region ............................ 13
     2.3  Traffic Classification and Conditioning ................... 14
       2.3.1  Classifiers ........................................... 14
       2.3.2  Traffic Profiles ...................................... 15
       2.3.3  Traffic Conditioners .................................. 15
         2.3.3.1  Meters ............................................ 16
         2.3.3.2  Markers ........................................... 16
         2.3.3.3  Shapers ........................................... 17
         2.3.3.4  Droppers .......................................... 17
       2.3.4  Location of Traffic Conditioners and MF Classifiers ... 17
         2.3.4.1  Within the Source Domain .......................... 17
         2.3.4.2  At the Boundary of a DS Domain .................... 18
         2.3.4.3  In non-DS-Capable Domains ......................... 18
         2.3.4.4  In Interior DS Nodes .............................. 19
     2.4  Per-Hop Behaviors ......................................... 19
     2.5  Network Resource Allocation ............................... 20
   3.  Per-Hop Behavior Specification Guidelines .................... 21
   4.  Interoperability with Non-Differentiated Services-Compliant
       Nodes ........................................................ 25
   5.  Multicast Considerations ..................................... 26
   6.  Security and Tunneling Considerations ........................ 27
     6.1  Theft and Denial of Service ............................... 28
     6.2  IPsec and Tunneling Interactions .......................... 30
     6.3  Auditing .................................................. 32
   7.  Acknowledgements ............................................. 32
   8.  References ................................................... 33
   Authors' Addresses ............................................... 34
   Full Copyright Statement ......................................... 36

1.  Introduction

1.1  Overview

   This document defines an architecture for implementing scalable
   service differentiation in the Internet.  A "Service" defines some
   significant characteristics of packet transmission in one direction
   across a set of one or more paths within a network.  These



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   characteristics may be specified in quantitative or statistical terms
   of throughput, delay, jitter, and/or loss, or may otherwise be
   specified in terms of some relative priority of access to network
   resources.  Service differentiation is desired to accommodate
   heterogeneous application requirements and user expectations, and to
   permit differentiated pricing of Internet service.

   This architecture is composed of a number of functional elements
   implemented in network nodes, including a small set of per-hop
   forwarding behaviors, packet classification functions, and traffic
   conditioning functions including metering, marking, shaping, and
   policing.  This architecture achieves scalability by implementing
   complex classification and conditioning functions only at network
   boundary nodes, and by applying per-hop behaviors to aggregates of
   traffic which have been appropriately marked using the DS field in
   the IPv4 or IPv6 headers [DSFIELD].  Per-hop behaviors are defined to
   permit a reasonably granular means of allocating buffer and bandwidth
   resources at each node among competing traffic streams.  Per-
   application flow or per-customer forwarding state need not be
   maintained within the core of the network.  A distinction is
   maintained between:

   o  the service provided to a traffic aggregate,

   o  the conditioning functions and per-hop behaviors used to realize
      services,

   o  the DS field value (DS codepoint) used to mark packets to select a
      per-hop behavior, and

   o  the particular node implementation mechanisms which realize a
      per-hop behavior.

   Service provisioning and traffic conditioning policies are
   sufficiently decoupled from the forwarding behaviors within the
   network interior to permit implementation of a wide variety of
   service behaviors, with room for future expansion.

   This architecture only provides service differentiation in one
   direction of traffic flow and is therefore asymmetric.  Development
   of a complementary symmetric architecture is a topic of current
   research but is outside the scope of this document; see for example
   [EXPLICIT].

   Sect. 1.2 is a glossary of terms used within this document.  Sec. 1.3
   lists requirements addressed by this architecture, and Sec. 1.4
   provides a brief comparison to other approaches for service
   differentiation.  Sec. 2 discusses the components of the architecture



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   in detail.  Sec. 3 proposes guidelines for per-hop behavior
   specifications.  Sec. 4 discusses interoperability issues with nodes
   and networks which do not implement differentiated services as
   defined in this document and in [DSFIELD].  Sec. 5 discusses issues
   with multicast service delivery.  Sec. 6 addresses security and
   tunnel considerations.

1.2  Terminology

   This section gives a general conceptual overview of the terms used in
   this document.  Some of these terms are more precisely defined in
   later sections of this document.

   Behavior Aggregate (BA)   a DS behavior aggregate.

   BA classifier             a classifier that selects packets based
                             only on the contents of the DS field.

   Boundary link             a link connecting the edge nodes of two
                             domains.

   Classifier                an entity which selects packets based on
                             the content of packet headers according to
                             defined rules.

   DS behavior aggregate     a collection of packets with the same DS
                             codepoint crossing a link in a particular
                             direction.

   DS boundary node          a DS node that connects one DS domain to a
                             node either in another DS domain or in a
                             domain that is not DS-capable.

   DS-capable                capable of implementing differentiated
                             services as described in this architecture;
                             usually used in reference to a domain
                             consisting of DS-compliant nodes.

   DS codepoint              a specific value of the DSCP portion of the
                             DS field, used to select a PHB.

   DS-compliant              enabled to support differentiated services
                             functions and behaviors as defined in
                             [DSFIELD], this document, and other
                             differentiated services documents; usually
                             used in reference to a node or device.





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   DS domain                 a DS-capable domain; a contiguous set of
                             nodes which operate with a common set of
                             service provisioning policies and PHB
                             definitions.

   DS egress node            a DS boundary node in its role in handling
                             traffic as it leaves a DS domain.

   DS ingress node           a DS boundary node in its role in handling
                             traffic as it enters a DS domain.

   DS interior node          a DS node that is not a DS boundary node.

   DS field                  the IPv4 header TOS octet or the IPv6
                             Traffic Class octet when interpreted in
                             conformance with the definition given in
                             [DSFIELD].  The bits of the DSCP field
                             encode the DS codepoint, while the
                             remaining bits are currently unused.

   DS node                   a DS-compliant node.

   DS region                 a set of contiguous DS domains which can
                             offer differentiated services over paths
                             across those DS domains.

   Downstream DS domain      the DS domain downstream of traffic flow on
                             a boundary link.

   Dropper                   a device that performs dropping.

   Dropping                  the process of discarding packets based on
                             specified rules; policing.

   Legacy node               a node which implements IPv4 Precedence as
                             defined in [RFC791,RFC1812] but which is
                             otherwise not DS-compliant.

   Marker                    a device that performs marking.

   Marking                   the process of setting the DS codepoint in
                             a packet based on defined rules; pre-
                             marking, re-marking.