Internet Engineering Task Force Juha Heinanen INTERNET DRAFT Telia Finland Expires August 1999 Roch Guerin University of Pennsylvania February, 1999 A Three Color Marker 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 http://www.ietf.org/ietf/1id-abstracts.txt 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. Heinanen & Guerin A Three Color Marker [Page 1] INTERNET DRAFT February, 1999 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 Marker codes the color into the DS field [Nichols] of the IP packet in a PHB specific manner (see section 4 for an example). 2. Configuration The user configures the TCM using 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 metering behavior of the TCM marker is specified in terms of 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, 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 Heinanen & Guerin A Three Color Marker [Page 2] INTERNET DRAFT February, 1999 o neither Tc nor Te is incremented. When a packet of size B bytes arrives at time t, the following happens: o If Tc(t)-B >= 0, the packet is marked green and Tc is decremented by B down to the minimum value of 0, else o if Te(t)-B >= 0, the packets is marked yellow and Te is decremented by B down to the minimum value of 0, else o the packet is marked 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. 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- Heinanen & Guerin A Three Color Marker [Page 3] INTERNET DRAFT February, 1999 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 Heinanen & Guerin A Three Color Marker [Page 4]