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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
+
+
+   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]
+
+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
+
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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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+
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+Heinanen & Guerin            Informational                      [Page 4]
+
+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]
+
+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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+Heinanen & Guerin            Informational                      [Page 6]
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