A Differentiated Service Two-Rate, Three-Color Marker with Efficient Handling of in-Profile Traffic
RFC 4115

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Network Working Group                                      O. Aboul-Magd
Request for Comments: 4115                                      S. Rabie
Category: Informational                                  Nortel Networks
                                                               July 2005

       A Differentiated Service Two-Rate, Three-Color Marker with
               Efficient Handling of in-Profile Traffic

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 (2005).

IESG Note

   This RFC is not a candidate for any level of Internet Standard.  The
   IETF disclaims any knowledge of the fitness of this RFC for any
   purpose and in particular notes that the decision to publish is not
   based on IETF review for such things as security, congestion control,
   or inappropriate interaction with deployed protocols.  The RFC Editor
   has chosen to publish this document at its discretion.  Readers of
   this document should exercise caution in evaluating its value for
   implementation and deployment.  See RFC 3932 for more information.

Abstract

   This document describes a two-rate, three-color marker that has been
   in use for data services including Frame Relay services.  This marker
   can be used for metering per-flow traffic in the emerging IP and L2
   VPN services.  The marker defined here is different from previously
   defined markers in the handling of the in-profile traffic.
   Furthermore, this marker doesn't impose peak-rate shaping
   requirements on customer edge (CE) devices.

1.  Introduction

   The differentiated service defines a quality-of-service (QoS)
   architecture for the Internet [RFC2475].  Two integral components of
   this architecture are traffic metering and marking.  This document
   describes a two-rate, three-color metering/marker algorithm that is

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RFC 4115        Efficient Handling of in-Profile Traffic       July 2005

   suitable for the differentiated service applications such as IP and
   L2 VPNs.  This algorithm has been in use for data services including
   Frame Relay Service.

   The metering/marker defined here is different from those in [RFC2697]
   and [RFC2698].  It is different from [RFC2697] in that it is a two-
   rate, three-color marker.  In contrast, [RFC2697] is a single-rate
   marker.  It is different from [RFC2698] in the way its parameters are
   defined, which allows a better handling of in-profile traffic for
   predominant service scenarios over a wider range of traffic
   parameters.

   Furthermore, the algorithm described here eliminates the need for the
   CE to shape its traffic to a certain peak information rate (PIR), as
   might be the case for the marker defined in [RFC2698] when the value
   for the peak burst size (PBS) is smaller than that for the committed
   burst size (CBS).

   The marker described here operates for both color-blind and color-
   aware modes, as defined in [RFC2698].

2.  Configuration

   The operation of the marker is described by two rate values.  The
   committed information rate (CIR) and the excess information rate
   (EIR).  CIR and EIR define the token generation rate of a token
   bucket with size that is equal to committed burst size (CBS) and
   excess burst size (EBS), respectively.

   The CBS and EBS are measured in bytes and must configure to be
   greater than the expected maximum length of the incoming PDU.  The
   CIR and EIR are both measured in bits/s.  The CIR and EIR can be set
   independently of each other.  Alternatively, the CIR and EIR can be
   linked together by defining a burst duration parameter, T, where
   T=CBS/CIR=EBS/EIR.

3.  Metering and Marking

   The behavior of the meter is defined in terms of its mode and two
   token buckets, C and E, with the rates, CIR and EIR, respectively,
   and maximum sizes CBS and EBS.

   The token buckets C and E are initially (at time 0) full; i.e., the
   token count Tc(0) = CBS and Te(0) = EBS.  Thereafter, the token count
   Tc is incremented by one CIR times per second (up to CBS), and the
   token count Te is incremented by one EIR times per second (up to
   EBS).

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RFC 4115        Efficient Handling of in-Profile Traffic       July 2005

   In the color-aware operation, it is assumed that the algorithm can
   recognize the color of the incoming packet (green, yellow, or red).
   The color-aware operation of the metering is described below.

   When a green packet of size B arrives at time t, then

      o  if Tc(t)- B > 0, the packet is green, and Tc(t) is decremented
         by B; else

      o  if Te(t)- B > 0, the packet is yellow, and Te(t) is decremented
         by B; else

      o  the packet is red.