Network Working Group B. Gaidioz Internet-Draft UCBL/ENS-Lyon Expires: August 23, 2002 P. Primet INRIA/ENS-Lyon February 22, 2002 The Equivalent Differentiated Services Model draft-gaidioz-equivalent-differentiated-services-00 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. This Internet-Draft will expire on August 23, 2002. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes EDS (Equivalent Differentiated Services), a new building-block for a simple, robust, free and scalable end-to-end service differentiation in IP networks. The EDS schema aims to provide a spectrum of "different but equal" network services that offer to the end-to-end flows a trade-off between delay and loss rate. The EDS schema can be deployed incrementally in the Internet. Gaidioz & Primet Expires August 23, 2002 [Page 1] Internet-Draft Equivalent Differentiated Services February 2002 1. Introduction and Requirements With the diversification of the Internet applications, flows sensitivity to loss or delay variations become more and more heterogeneous. There is an important need for service differentiation at the IP layer. Some flows require better delay, other better loss rate than those offered by a flat best-effort service. For example, it is well known that audio streams are perturbed by important delay variations, but different TCP flows may also react variously to loss rate or delay patterns according they are long and bulk or short and carrying interactive information. Improving the best-effort service of Internet by adding pertinent differentiation mechanisms and simultaneously remaining close to the IP philosophy [3], [4] is an important challenge. Any such improvement of the IP stack has to respect the following criteria: o the building block has to be simple, robust and scalable, o the building block can be incrementally deployed. o the various services must be freely usable as the unique best- effort service provided by today's IP networks. Neither pricing nor admission control must be performed, Queue management systems such as RED [9] or ECN [8] mechanisms tend to improve the best-effort service by having more control on congestion. Even if they do respect the IP philosophy and meet the criteria, they do not provide explicit differentiated services to applications. Pricing can be avoided only if the proposed services cannot be ordered in the sense that one is better than another. Consequently, even if flows do get different performances, when a flows gains on one side, it has to loose something on an other side. This is the underlying principle of "non-elevated services" [5] like ABE [1] or BEDS [2]. Admission control can be avoided only if guarantees are relative rather than absolute. Absolute guarantees requires resource provisioning, admission control and traffic control to ensure traffic does not exceed a given rate. If guarantees are relative, they can still be ensured, whatever the network load is. The simplicity requirement restrict the potential treatment of individual packets. The performances of the network layer must remain high and compatible with the actual link speeds. Today's router are able to classify packets and to treat them differently in Gaidioz & Primet Expires August 23, 2002 [Page 2] Internet-Draft Equivalent Differentiated Services February 2002 different queues efficiently. But, with the improvement of the optical technology and the exponential increase of the network capacity, the complexity of packet processing performed by network routers at ultra high speed cannot increase much. The robustness requirement implies that the network remains end-to- end stateless. The incremental deployment means that the schema must support service differentiation only performed partially along the end-to-end path. EDS proposes a new building block at the IP level that aims to differentiate the per hop behavior (PHB) to better meet the needs of each flows and that respect the preceding criteria. The EDS schema aims to provide a spectrum of different but equal services, said equivalent, that offer a trade-off between delay and loss rate. 2. Specifications The EDS defines an arbitrary number N of equivalent service classes (N greater or equal to 2) which are identified by numbers ranging from `1' to `N'. The services are directly used by end-to-end protocols or applications [4]. Each "EDS-capable router" differentiates among classes over the queuing delay of the packets and their loss rate. A class `i' is given two constant coefficients `d_i' (the delay coefficient) and `l_i' (the loss rate coefficient) defined as follows. Let `i' and `j' be two different classes: in each router, a ratio of d_i/d_j between the queuing delays of their packet and a ratio of l_i/l_j between their loss rates are defined. Coefficients are set so that for each i in [1,N-1], l_i+1 is higher than l_i and d_i+1 is lower than d_i. Class `1' is thus the class whose packets experience the lowest loss rate and the highest queuing delay ; packets of class `N' gets the highest loss rate and the lowest queuing delay. Packets of classes `i' where 1