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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.
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+Heinanen & Guerin Informational [Page 1]
+
+RFC 2697 A Single Rate Three Color Marker September 1999
+
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+ 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.
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+Heinanen & Guerin Informational [Page 2]
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+RFC 2697 A Single Rate Three Color Marker September 1999
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+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
+
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+Heinanen & Guerin Informational [Page 3]
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+RFC 2697 A Single Rate Three Color Marker September 1999
+
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+ 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.
+
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+Heinanen & Guerin Informational [Page 4]
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+RFC 2697 A Single Rate Three Color Marker September 1999
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+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
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+Heinanen & Guerin Informational [Page 5]
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+RFC 2697 A Single Rate Three Color Marker September 1999
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+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.
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