Internet DRAFT - draft-heinanen-diffserv-tcm

draft-heinanen-diffserv-tcm



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Internet Engineering Task Force                            Juha Heinanen
INTERNET DRAFT                                             Telia Finland
Expires August 1999                                          Roch Guerin
                                              University of Pennsylvania
                                                          February, 1999


                          A Three Color Marker
                  <draft-heinanen-diffserv-tcm-01.txt>


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   Distribution of this memo is unlimited.

Abstract

   This document defines a Three Color Marker (TCM), which can be used
   as component in a Diffserv traffic conditioner [RFC2475, RFC2474].
   The TCM 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.  The TCM is useful, for example, in policing a
   service, where green, yellow, and red packets are forwarded with
   increasing discard probability.







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1. Introduction

   The Three Color Marker (TCM) meters an IP packet stream and marks its
   packets either green, yellow, or red.  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 the packet stream has been
   precolored.

   The Marker (re)colors an IP packet according to the results of the
   Meter.  The color is coded in the DS field [Nichols] of the packet in
   a PHB specific manner (see section 4 for an example).

2. Configuration

   The TCM is configured by setting its mode and by assigning values to
   the 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.

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 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,



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INTERNET DRAFT                                            February, 1999


   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 TCM 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 Tc is decremented.

   When a packet of size B bytes arrives at time t, the following
   happens if the TCM 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 Tc is decremented.

   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
   [Heinanen], the color can be coded as the drop precedence of the
   packet.

5. Service Example

   The TCM 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.



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6. Discussion

   The TCM specified in this document is by no means the only possible
   way to color packets.  Another three color marker could be defined,
   for example, by giving the green and yellow packets their own
   committed information rates.  Possible specification of other
   multicolor markers is left for future study in other documents.

7. Security Concerns

   The TCM has no known security concerns.

8. References

   [Heinanen] J. Heinanen, et al., Assured Forwarding PHB Group.
   Internet draft draft-ietf-diffserv-af-05.txt, February 1999.

   [Nichols] K. Nichols and B. Carpenter, Format for Diffserv Working
   Group Traffic Conditioner Drafts. Internet draft draft-ietf-diffserv-
   traffcon-format-00.txt, February 1999.

   [RFC2474] K. Nichols, et al., Definition of the Differentiated
   Services Field (DS Field) in the IPv4 and IPv6 Headers.  RFC 2474,
   December 1998.

   [RFC2475] S. Blake, et al., An Architecture for Differentiated
   Services. RFC 2475, December 1998.

9. Author 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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