Internet Engineering Task Force M. Menth Internet-Draft F. Lehrieder Expires: January 8, 2009 University of Wuerzburg July 7, 2008 Marking Converter for Excess-Marked Traffic draft-menth-pcn-marking-converter-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 January 8, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). Menth & Lehrieder Expires January 8, 2009 [Page 1] Internet-Draft PCN Marking Converter July 2008 Abstract This document proposes an algorithm that converts packet markings of a stream that was excess-marked based on a lower-rate into packet markings that correspond to a stream that was excess-marked based on a higher-rate. It may be applied in the PCN context to convert marked admissible-rate-overload into marked supportable-rate- overload. This allows to perform marked flow termination when packets are excess-marked based on the admissible rate only. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Algorithm for Conversion of AS-Markings into ET-Markings . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . . 10 7.3. Other References . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Intellectual Property and Copyright Statements . . . . . . . . . . 12 Menth & Lehrieder Expires January 8, 2009 [Page 2] Internet-Draft PCN Marking Converter July 2008 1. Introduction Pre-congestion notification provides information to support admission control and flow termination at the boundary nodes of a Diffserv region in order to protect the quality of service (QoS) of inelastic flows [I-D.ietf-pcn-architecture]. This is achieved by marking packets on interior nodes according to some metering function implemented at each node. Links are associated with an admissible and a supportable rate threshold (AR, SR). o When the PCN traffic rate on a link exceeds the AR of that link, the link is AR-pre-congested and the PCN rate above AR is AR- overload. o When the PCN traffic rate on a link exceeds the SR of that link, the link is SR-pre-congested and the PCN rate above SR is SR- overload. Excess marking is a mechanism marking packets exceeding a certain reference rate. If applied with AR or SR as reference rate on a link of the PCN domain, excess marking marks the AR- or SR-overload. We call the marks based on AR admission-stop (AS) marking and the marks based on SR excess-traffic (ET) marking. Admission control requires AS-marking while flow termination requires ET-marking. Having two different markers is desirable to perform admission control and flow termination based on direct feedback from the network, but it increases hardware and encoding complexity. The single-marking draft [I-D.charny-pcn-single-marking] proposes one method to perform measured rate termination based on AR-overload. It requires that SR=u*AR on all links within the PCN domain. In this document we present a conversion algorithm that converts AS- markings of a packet stream into ET-markings. Admission control can be performed based on the original AS-markings and flow termination can be performed based on the converted ET-markings. To that end, any flow termination method working with SR-overload can be applied ([Menth08-PCN-Comparison], Section 7). The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Menth & Lehrieder Expires January 8, 2009 [Page 3] Internet-Draft PCN Marking Converter July 2008 2. Terminology Most of the terminology used in this document is defined in [I-D.ietf-pcn-architecture]. The following additional terms are defined. o Admissible rate (AR) - PCN lower rate o Supportable rate (SR) - PCN upper rate o AR-overload - PCN traffic rate above AR o SR-overload - PCN traffic rate above SR o Excess marking - metering and marking mechanism marking all packets exceeding a reference rate (excess rate marking in [I-D.eardley-pcn-marking-behaviour]) o Admission-stop (AS) marking - marking based on AR as reference rate o Excess-traffic (ET) marking - marking based on SR as reference rate Menth & Lehrieder Expires January 8, 2009 [Page 4] Internet-Draft PCN Marking Converter July 2008 3. Algorithm for Conversion of AS-Markings into ET-Markings The conversion algorithm is applied by the egress node on an ingress- egress aggregate basis. It is called for each packet arrival and either converts an existing AS-mark into an ET-mark or clears it. The algorithm is based on a token bucket (TB) with size S, fill state F, and threshold T. It differs from conventional TB implementations as it does not have a constant fill rate R. Its operation is explained in Algorithm 1. Algorithm 1: Input: token bucket parameters S, F, and T, packet size B and marking M 1: if (M == unmarked) then 2: F = min(S, F + (u - 1) * B); 3: else if (F >= T) then 4: F = F - B; 5: M = unmarked; 6: else 7: M = ET; 8: end if The number of tokens in the bucket F indicates how many AS-marked bytes can be re-marked to unmarked. Initially, the token bucket should be filled. For each non-AS-marked byte, the fill state F is incremented by u-1 tokens (cf. line 1-2). When a packet arrives AS- marked and if the fill state F is larger than a certain threshold T, the packet is re-marked to unmarked and the fill state of the TB is reduced by the packet size B. Otherwise, the packet remains marked which is then interpreted as ET-marking (cf. line 3-8). The threshold T is used to achieve packet-size independent marking conversion and should be set to the maximum transfer unit. A sufficiently large TB size S is needed to tolerate short-term variations of packet markings, i.e. a burst of S AS-marked bytes should not be ET-marked. However, this tolerance also delays initial re-marking. Further experimentation and performance evaluation of this approach is required. First simulations give a proof of concept. The conversion algorithm works well if the rate of the controlled ingress-egress-aggregate is large enough and if it is a rather large fraction (>10%) of the traffic rate on the bottleneck link. If this is not the case, packets with AS-markings occur almost random which leads to a geometrically distributed distance between packet markings within an ingress-egress-aggregate such that very large bursts of AS-marked packets can occur even when the PCN rate is between AR and SR on the Menth & Lehrieder Expires January 8, 2009 [Page 5] Internet-Draft PCN Marking Converter July 2008 bottleneck link. This leads to wrong ET-markings. As a result, there is some chance for overtermination ([I-D.menth-pcn-performance]) when marked flow termination for ingress-egress-aggregates is used. This, however, is not a property of the conversion algorithm, it's rather a property of the single marking approach and also measured rate termination suffers from this phenomenon. Further evaluation is required to configure the conversion algorithm appropriately and to validate flow termination mechanisms in combination with this converter. Menth & Lehrieder Expires January 8, 2009 [Page 6] Internet-Draft PCN Marking Converter July 2008 4. IANA Considerations TBD Menth & Lehrieder Expires January 8, 2009 [Page 7] Internet-Draft PCN Marking Converter July 2008 5. Security Considerations TBD Menth & Lehrieder Expires January 8, 2009 [Page 8] Internet-Draft PCN Marking Converter July 2008 6. Conclusion This document describes an algorithm that converts marked AR-overload into marked SR-overload. It makes flow termination mechanisms requiring SR-overload applicable in networks that mark AR-overload only. This algorithm does not solve the problem that flow termination based on AR-overload does not work well for multipath routing ([Menth08-PCN-Comparison], Section 8.3). Menth & Lehrieder Expires January 8, 2009 [Page 9] Internet-Draft PCN Marking Converter July 2008 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7.2. Informative References [I-D.charny-pcn-single-marking] Charny, A., Zhang, X., Faucheur, F., and V. Liatsos, "Pre- Congestion Notification Using Single Marking for Admission and Termination", draft-charny-pcn-single-marking-03 (work in progress), November 2007. [I-D.eardley-pcn-marking-behaviour] Eardley, P., "", draft-eardley-pcn-marking-behaviour-01 (work in progress), I-D Status active, June 2008. [I-D.ietf-pcn-architecture] Eardley, P., "Pre-Congestion Notification Architecture", draft-ietf-pcn-architecture-01 (work in progress), October 2007. [I-D.menth-pcn-performance] Menth, M. and F. Lehrieder, "Performance Evaluation of PCN-Based Algorithms", draft-menth-pcn-performance-02 (work in progress), February 2008. 7.3. Other References [Menth08-PCN-Comparison] Menth, M., Lehrieder, F., Briscoe, B., Eardley, P., Moncaster, T., Babiarz, J., Chan, K., Charny, A., Karagiannis, G., and X. Zhang, "PCN-Based Admission Control and Flow Termination", 2008, . Menth & Lehrieder Expires January 8, 2009 [Page 10] Internet-Draft PCN Marking Converter July 2008 Authors' Addresses Michael Menth University of Wuerzburg Am Hubland Wuerzburg D-97074 Germany Phone: +49-931-888-6644 Email: menth@informatik.uni-wuerzburg.de Frank Lehrieder University of Wuerzburg Am Hubland Wuerzburg D-97074 Germany Phone: +49-931-888-6651 Email: lehrieder@informatik.uni-wuerzburg.de Menth & Lehrieder Expires January 8, 2009 [Page 11] Internet-Draft PCN Marking Converter July 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Menth & Lehrieder Expires January 8, 2009 [Page 12]