<?xml version='1.0'?>

<reference anchor='RFC2474'>

<front>
<title abbrev='Differentiated Services Field'>Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers</title>
<author initials='K.' surname='Nichols' fullname='Kathleen Nichols'>
<organization>Cisco Systems</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<city>San Jose</city>
<region>CA</region>
<code>95134-1706</code>
<country>USA</country></postal>
<phone>+1 408 525 4857</phone>
<email>kmn@cisco.com</email></address></author>
<author initials='S.' surname='Blake' fullname='Steven Blake'>
<organization>Torrent Networking Technologies</organization>
<address>
<postal>
<street>3000 Aerial Center</street>
<city>Morrisville</city>
<region>NC</region>
<code>27560</code>
<country>USA</country></postal>
<phone>+1 919 468 8466 x232</phone>
<email>slblake@torrentnet.com</email></address></author>
<author initials='F.' surname='Baker' fullname='Fred Baker'>
<organization>Cisco Systems</organization>
<address>
<postal>
<street>519 Lado Drive</street>
<city> Santa Barbara</city>
<region>CA</region>
<code>93111</code>
<country>USA</country></postal>
<phone>+1 408 526 4257</phone>
<email>fred@cisco.com</email></address></author>
<author initials='D.L.' surname='Black' fullname='David L. Black'>
<organization>EMC Corporation</organization>
<address>
<postal>
<street>35 Parkwood Drive</street>
<city>Hopkinton</city>
<region>MA</region>
<code>01748</code>
<country>USA</country></postal>
<phone>+1 508 435 1000 x76140</phone>
<email>black_david@emc.com</email></address></author>
<date month='December' year='1998' />
<area>Internet</area>
<keyword>internet protocol version 4</keyword>
<keyword>IPv6</keyword>
<keyword>IPv4</keyword>
<keyword>internet protocol version 6</keyword>
<keyword>type of service</keyword>
<abstract>
<t>
   Differentiated services enhancements to the Internet protocol are
   intended to enable scalable service discrimination in the Internet
   without the need for per-flow state and signaling at every hop.  A
   variety of services may be built from a small, well-defined set of
   building blocks which are deployed in network nodes.  The services
   may be either end-to-end or intra-domain; they include both those
   that can satisfy quantitative performance requirements (e.g., peak
   bandwidth) and those based on relative performance (e.g., &quot;class&quot;
   differentiation).  Services can be constructed by a combination of:

<list>
<t>
   - setting bits in an IP header field at network boundaries
     (autonomous system boundaries, internal administrative boundaries,
     or hosts),
</t>
<t>
   - using those bits to determine how packets are forwarded by the
     nodes inside the network, and
</t>
<t>
   - conditioning the marked packets at network boundaries in accordance
     with the requirements or rules of each service.
</t></list></t>
<t>
   The requirements or rules of each service must be set through
   administrative policy mechanisms which are outside the scope of this
   document.  A differentiated services-compliant network node includes
   a classifier that selects packets based on the value of the DS field,
   along with buffer management and packet scheduling mechanisms capable
   of delivering the specific packet forwarding treatment indicated by
   the DS field value.  Setting of the DS field and conditioning of the
   temporal behavior of marked packets need only be performed at network
   boundaries and may vary in complexity.
</t>
<t>
   This document defines the IP header field, called the DS (for
   differentiated services) field.  In IPv4, it defines the layout of
   the TOS octet; in IPv6, the Traffic Class octet.  In addition, a base
   set of packet forwarding treatments, or per-hop behaviors, is
   defined.
</t>
<t>
   For a more complete understanding of differentiated services, see
   also the differentiated services architecture .
</t></abstract></front>

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