A Single Rate Three Color Marker
RFC 2697

Document Type RFC - Informational (September 1999; No errata)
Last updated 2013-03-02
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Network Working Group                                        J. Heinanen
Request for Comments: 2697                                 Telia Finland
Category: Informational                                        R. Guerin
                                              University of Pennsylvania
                                                          September 1999

                    A Single Rate Three Color Marker

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 (1999).  All Rights Reserved.

Abstract

   This document defines a Single Rate Three Color Marker (srTCM), which
   can be used as component in a Diffserv traffic conditioner [RFC2475,
   RFC2474].  The srTCM meters a traffic stream and marks its packets
   according to three traffic parameters, Committed Information Rate
   (CIR), Committed Burst Size (CBS), and Excess Burst Size (EBS), to be
   either green, yellow, or red.  A packet is marked green if it doesn't
   exceed the CBS, yellow if it does exceed the CBS, but not the EBS,
   and red otherwise.

1. Introduction

   The Single Rate Three Color Marker (srTCM) meters an IP packet stream
   and marks its packets either green, yellow, or red.  Marking is based
   on a Committed Information Rate (CIR) and two associated burst sizes,
   a Committed Burst Size (CBS) and an Excess Burst Size (EBS).  A
   packet is marked green if it doesn't exceed the CBS, yellow if it
   does exceed the CBS, but not the EBS, and red otherwise.  The srTCM
   is useful, for example, for ingress policing of a service, where only
   the length, not the peak rate, of the burst determines service
   eligibility.

Heinanen & Guerin            Informational                      [Page 1]
RFC 2697            A Single Rate Three Color Marker      September 1999

   The Meter meters each packet and passes the packet and the metering
   result to the Marker:

                     +------------+
                     |   Result   |
                     |            V
                 +-------+    +--------+
                 |       |    |        |
      Packet Stream ===>| Meter |===>| Marker |===> Marked Packet Stream
                 |       |    |        |
                 +-------+    +--------+

   The Meter operates in one of two modes.  In the Color-Blind mode, the
   Meter assumes that the packet stream is uncolored.  In the Color-
   Aware mode the Meter assumes that some preceding entity has pre-
   colored the incoming packet stream so that each packet is either
   green, yellow, or red.  The details of the pre-coloring process,
   including handling of error scenarios, and how the Meter determines
   the color of a pre-colored packet are DS domain specific and outside
   the scope of this document.

   The Marker (re)colors an IP packet according to the results of the
   Meter.  The color is coded in the DS field [RFC2474] of the packet in
   a PHB specific manner (see section 4 for an example).

   A companion document [RFC2698] describes another three color marker,
   called a Two Rate Three Color Maker (trTCM), where packets are marked
   based on two rates and two burst sizes.

2. Configuration

   The srTCM is configured by setting its mode and by assigning values
   to three traffic parameters: a Committed Information Rate (CIR), a
   Committed Burst Size (CBS), and an Excess Burst Size (EBS).

   The CIR is measured in bytes of IP packets per second, i.e., it
   includes the IP header, but not link specific headers.

   The CBS and the EBS and are measured in bytes.  The CBS and EBS must
   be configured so that at least one of them is larger than 0.  It is
   recommended that when the value of the CBS or the EBS is larger than
   0, it is larger than or equal to the size of the largest possible IP
   packet in the stream.

Heinanen & Guerin            Informational                      [Page 2]
RFC 2697            A Single Rate Three Color Marker      September 1999

3. Metering

   The behavior of the Meter is specified in terms of its mode and two
   token buckets, C and E, which both share the common rate CIR.  The
   maximum size of the token bucket C is CBS and the maximum size of the
   token bucket E is EBS.

   The token buckets C and E are initially (at time 0) full, i.e., the
   token count Tc(0) = CBS and the token count Te(0) = EBS.  Thereafter,
   the token counts Tc and Te are updated CIR times per second as
   follows:

     o If Tc is less than CBS, Tc is incremented by one, else

     o if Te is less then EBS, Te is incremented by one, else

     o neither Tc nor Te is incremented.

   When a packet of size B bytes arrives at time t, the following
   happens if the srTCM is configured to operate in the Color-Blind
   mode:

     o If Tc(t)-B >= 0, the packet is green and Tc is decremented by B
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