Network Working Group J. Heinanen
Request for Comments: 2698 Telia Finland
Category: Informational R. Guerin
University of Pennsylvania
September 1999

A Two 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 Two Rate Three Color Marker (trTCM), which
can be used as a component in a Diffserv traffic conditioner
[RFC2475, RFC2474]. The trTCM meters an IP packet stream and marks
its packets based on two rates, Peak Information Rate (PIR) and
Committed Information Rate (CIR), and their associated burst sizes to
be either green, yellow, or red. A packet is marked red if it
exceeds the PIR. Otherwise it is marked either yellow or green
depending on whether it exceeds or doesn't exceed the CIR.

1. IntrodUCtion

The Two Rate Three Color Marker (trTCM) meters an IP packet stream
and marks its packets either green, yellow, or red. A packet is
marked red if it exceeds the Peak Information Rate (PIR). Otherwise
it is marked either yellow or green depending on whether it exceeds
or doesn't exceed the Committed Information Rate (CIR). The trTCM is
useful, for example, for ingress policing of a service, where a peak
rate needs to be enforced separately from a committed rate.

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 [RFC2697] describes another three color marker,
called a Single Rate Three Color Maker (srTCM), where packets are
marked based on a single rate and two burst sizes.

2. Configuration

The trTCM is configured by setting its mode and by assigning values
to four traffic parameters: a Peak Information Rate (PIR) and its
associated Peak Burst Size (PBS) and a Committed Information Rate
(CIR) and its associated Committed Burst Size (CBS).

The PIR and CIR are measured in bytes of IP packets per second, i.e.,
it includes the IP header, but not link specific headers. The PIR
must be equal to or greater than the CIR.

The PBS and the CBS and are measured in bytes and both of them must
be configured to be greater than 0. It is recommended that they be
configured to be equal to or greater than the size of the largest
possible IP packet in the stream.

3. Metering

The behavior of the Meter is specified in terms of its mode and two
token buckets, P and C, with rates PIR and CIR, respectively. The
maximum size of the token bucket P is PBS and the maximum size of the
token bucket C is CBS.

The token buckets P and C are initially (at time 0) full, i.e., the
token count Tp(0) = PBS and the token count Tc(0) = CBS. Thereafter,
the token count Tp is incremented by one PIR times per second up to
PBS and the token count Tc is incremented by one CIR times per second
up to CBS.

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

o If Tp(t)-B < 0, the packet is red, else

o if Tc(t)-B < 0, the packet is yellow and Tp is decremented by B,
else

o the packet is green and both Tp and Tc are decremented by B.

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

o If the packet has been precolored as red or if Tp(t)-B < 0, the
packet is red, else

o if the packet has been precolored as yellow or if Tc(t)-B < 0,
the packet is yellow and Tp is decremented by B, else

o the packet is green and both Tp and Tc are decremented by B.

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 trTCM can be used to mark a IP 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
the peak rate, forward yellow packets as best effort, and forward
green packets with a low drop probability.

6. Security Considerations

The trTCM has no known security concerns.

7. References

[RFC2697] Heinanen, J. and R. Guerin, "A Single Rate Three Color
Marker", RFC2697, September 1999.

[RFC2597] Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
"Assured Forwarding PHB Group", RFC2597, 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", RFC2474, December
1998.

[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z
and W. Weiss, "An Architecture for Differentiated
Services", RFC2475, December 1998.

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 367 GRW
200 South 33rd Street
PhilaDelphia, PA 19104

EMail: guerin@ee.upenn.edu

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