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rfc:rfc2697

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
     down to the minimum value of 0, else
   o if Te(t)-B >= 0, the packets is yellow and Te is decremented by B
     down to the minimum value of 0, else
   o the packet is red and neither Tc nor Te is decremented.
 When a packet of size B bytes arrives at time t, the following
 happens if the srTCM is configured to operate in the Color-Aware
 mode:
   o If the packet has been precolored as green and Tc(t)-B >= 0, the
     packet is green and Tc is decremented by B down to the minimum
     value of 0, else
   o If the packet has been precolored as green or yellow and if
     Te(t)-B >= 0, the packets is yellow and Te is decremented by B
     down to the minimum value of 0, else
   o the packet is red and neither Tc nor Te is decremented.
 Note that according to the above rules, marking of a packet with a
 given color requires that there be enough tokens of that color to
 accommodate the entire packet.  Other marking policies are clearly
 possible. The above policy was chosen in order guarantee a

Heinanen & Guerin Informational [Page 3] RFC 2697 A Single Rate Three Color Marker September 1999

 deterministic behavior where the volume of green packets is never
 smaller than what has been determined by the CIR and CBS, i.e.,
 tokens of a given color are always spent on packets of that color.
 The actual implementation of a Meter doesn't need to be modeled
 according to the above formal specification.

4. Marking

 The Marker reflects the metering result by setting the DS field of
 the packet to a particular codepoint.  In case of the AF PHB
 [RFC2597], the color can be coded as the drop precedence of the
 packet.

5. Service Example

 The srTCM can be used to mark a packet stream in a service, where
 different, decreasing levels of assurances (either absolute or
 relative) are given to packets which are green, yellow, or red.  For
 example, a service may discard all red packets, because they exceeded
 both the committed and excess burst sizes, forward yellow packets as
 best effort, and forward green packets with a low drop probability.

6. Security Considerations

 The srTCM has no known security concerns.

7. References

 [RFC2698] Heinanen, J. and R. Guerin, "A Two Rate Three Color
             Marker", RFC 2698, September 1999.
 [RFC2597] Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
             "Assured Forwarding PHB Group", RFC 2597, June 1999.
 [RFC2474]   Nichols, K., Blake, S., Baker, F. and D. Black,
             "Definition of the Differentiated Services Field (DS
             Field) in the IPv4 and IPv6 Headers", RFC 2474, December
             1998.
 [RFC2475]   Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
             and W. Weiss, "An Architecture for Differentiated
             Services", RFC 2475, December 1998.

Heinanen & Guerin Informational [Page 4] RFC 2697 A Single Rate Three Color Marker September 1999

8. Authors' Addresses

 Juha Heinanen
 Telia Finland, Inc.
 Myyrmaentie 2
 01600 Vantaa, Finland
 EMail: jh@telia.fi
 Roch Guerin
 University of Pennsylvania
 Department of Electrical Engineering, Rm 376 GRW
 200 South 33rd Street
 Philadelphia, PA 19104
 EMail: guerin@ee.upenn.edu

Heinanen & Guerin Informational [Page 5] RFC 2697 A Single Rate Three Color Marker September 1999

9. Full Copyright Statement

 Copyright (C) The Internet Society (1999).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Heinanen & Guerin Informational [Page 6]

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