Congestion and Pre-Congestion M. Menth Internet-Draft University of Tuebingen Intended status: Experimental R. Geib Expires: September 1, 2011 Deutsche Telekom February 28, 2011 Admission Control Using PCN-Marked Signaling draft-menth-pcn-marked-signaling-ac-00 Abstract Pre-congestion notification (PCN) is a means for protecting quality of service for inelastic traffic admitted to a Diffserv domain. The overall PCN architecture is described in RFC5559. This memo is one of a series describing possible boundary node behaviours for a PCN domain. This document proposes an admission control method. It assumes that PCN nodes perform threshold-marking configured with the PCN- admissible-rate on any link. The PCN marking state of an initial signaling message of a flow is used to determine whether the flow should be admitted or blocked. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on September 1, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents Menth & Geib Expires September 1, 2011 [Page 1] Internet-Draft AC Using PCN-Marked Signaling February 2011 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Assumed Core Network Behaviour for PCN-marked signaling . . . . 3 3. Edge Node Behaviours . . . . . . . . . . . . . . . . . . . . . 4 3.1. Prerequisites . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Behavior of PCN-Ingress-Nodes . . . . . . . . . . . . . . . 4 3.3. Behavior of PCN-Egress-Nodes . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6 8.2. Informative References . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Menth & Geib Expires September 1, 2011 [Page 2] Internet-Draft AC Using PCN-Marked Signaling February 2011 1. Introduction The objective of Pre-Congestion Notification (PCN) is to protect the quality of service (QoS) of inelastic flows within a Diffserv domain, in a simple, scalable, and robust fashion. Two mechanisms are used: admission control, to decide whether to admit or block a new flow request, and flow termination to decide whether to terminate some already admitted flows during serious congestion. To achieve this, the overall rate of PCN-traffic is metered on every link in the domain, and PCN-packets are appropriately remarked when certain configured rates are exceeded. These configured rates are below the rate of the link thus providing notification to boundary nodes about overloads before any congestion occurs (hence the "pre" part of pre- congestion notification). For more details see [RFC5559]. This document presents PCN-marked signaling as a method to perform admission control based on PCN information. It requires that all PCN-ingress-nodes perform threshold marking [RFC5670] configured with the PCN-admissible-rate as reference rate, and uses the marking state of initial signaling messages to determine whether flows should be admitted or blocked. It neither describes a corresponding flow termination behavior nor does it preclude flow termination. The proposed method has several benefits: it does not require any measurement, it blocks very quickly as soon as pre-congestion occurs [Menth08-Sub-8], and it works well with multipath routing if signaling messages are carried on the same path as future data packets. 1.1. Terminology 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 [RFC2119]. The terminology defined in [RFC5559] applies. 2. Assumed Core Network Behaviour for PCN-marked signaling Admission control using PCN-marked signaling requires that nodes of a PCN-domain perform threshold marking [RFC5670]. The reference rate must be set to the PCN-admissible-rate of a link. Either Baseline Encoding [RFC5696] or 3-in-1 Encoding [I-D.ietf-pcn-3-in-1-encoding] may be used to distinguish re-marked signaling packets from unmarked signaling packets. Menth & Geib Expires September 1, 2011 [Page 3] Internet-Draft AC Using PCN-Marked Signaling February 2011 3. Edge Node Behaviours This section explains the behavior of PCN-ingress-nodes and PCN- egress-nodes. 3.1. Prerequisites PCN-marked signaling assumes that admission control is triggered by a signaling message at the PCN-ingress-node and that this signaling message is carried across the PCN-domain to the PCN-egress-node on the same path as future data packets of the associated flow. These signaling messages are processed only by PCN-ingress-nodes and PCN- egress-nodes. An example for such a signaling is the Resource ReServation Protocol [RFC2205]. PCN-marked signaling is relatively simple to implement when either PCN-ingress-node or PCN-egress-node are involved in the signaling anyway. 3.2. Behavior of PCN-Ingress-Nodes The PCN-ingress-node re-marks signaling messages to PCN not-marked (NM) so that they are subject to metering and re-marking by PCN- interior-nodes. Note that signaling packets need to be marked as PCN not-marked (NM) only as long as the flow is not yet admitted. In case of RSVP, the PCN-ingress-node performs the following non- standard actions. If the PCN-ingress-node receives a PATH message, it re-marks it to NM. If the PCN-ingress-node receives an initial RESV message, it admits the flow for the hop over the PCN domain and forwards the RESV message to the previous RSVP-hop on the path. 3.3. Behavior of PCN-Egress-Nodes The PCN-egress-node detects signaling messages. As long as the flow is not yet admitted, the PCN-egress-node evaluates the PCN codepoint of received signaling messages. If the codepoint is NM, it takes actions so that the flow can be admitted; otherwise it takes actions so that the flow will be blocked. Finally, the PCN-egress-node resets the PCN codepoint to not-PCN. In case of RSVP, the PCN-egress-node performs the following non- standard actions. If the PCN-egress-node receives an initial not- marked PATH message, the PCN-egress-node forwards the message as usual. If the PCN-egress-node receives an initial re-marked PATH message, the PCN-egress-node drops the PATH message and returns a PATH TEAR message to the previous RSVP hop indicating insufficient resources. Menth & Geib Expires September 1, 2011 [Page 4] Internet-Draft AC Using PCN-Marked Signaling February 2011 4. IANA Considerations This document makes no request to IANA. 5. Security Considerations Please see the security considerations in [RFC2205], [RFC2474], and [RFC2475]. [RFC5559] provides a general description of the security considerations for PCN. 6. Conclusions The PCN-based admission control method proposed in this document has several benefits. It does not require any measurement and does not require any parameters except for threshold metering and re-marking. Implicit probing blocks very quickly as soon as pre-congestion occurs [Menth08-Sub-8] and leads to less over-admission than PCN-based admission control that calculates congestion level estimates per ingress-egress aggregate to derive admission decisions. Moreover, Implicit Probing works well with multipath routing when the signaling message is carried on the same path as future data packets [Menth08-Sub-8]. Admission control using PCN-marked signaling as proposed in this document is simple provided that the admission of flows is requested by a path-coupled signaling protocol (e.g. RSVP). In contrast to other approaches [I-D.ietf-pcn-cl-edge-behaviour], [I-D.ietf-pcn-sm-edge-behaviour] PCN-egress-nodes neither need to measure PCN traffic nor need to signal PCN-feedback. In particular, pcn-egress-nodes no longer need to map packets to corresponding ingress-egress-aggregates. Moreover, the presented method blocks very quickly as soon as pre-congestion occurs [Menth08-Sub-8], minimizing over-admission. It also works well with multipath routing if signaling messages are carried on the same path as future data packets [Menth08-Sub-8], minimizing under-admission. 7. Acknowledgements Joe Babiarz presented the idea documented in this memo for the first time in [I-D.babiarz-pcn-3sm]. It was further developed to be useful for restricted tunneling rules which called for a special encoding [I-D.ietf-pcn-psdm-encoding], [I-D.menth-pcn-psdm-deployment], [Menth09f]. 8. References Menth & Geib Expires September 1, 2011 [Page 5] Internet-Draft AC Using PCN-Marked Signaling February 2011 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, September 1997. [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC 2474, December 1998. [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., and W. Weiss, "An Architecture for Differentiated Services", RFC 2475, December 1998. [RFC5559] Eardley, P., "Pre-Congestion Notification (PCN) Architecture", RFC 5559, June 2009. [RFC5670] Eardley, P., "Metering and Marking Behaviour of PCN- Nodes", RFC 5670, November 2009. [RFC5696] Moncaster, T., Briscoe, B., and M. Menth, "Baseline Encoding and Transport of Pre-Congestion Information", RFC 5696, November 2009. 8.2. Informative References [I-D.babiarz-pcn-3sm] Babiarz, J., Liu, X., Chan, K., and M. Menth, "Three State PCN Marking", draft-babiarz-pcn-3sm-01 (work in progress), November 2007. [I-D.ietf-pcn-3-in-1-encoding] Briscoe, B., Moncaster, T., and M. Menth, "Encoding 3 PCN- States in the IP header using a single DSCP", draft-ietf-pcn-3-in-1-encoding-04 (work in progress), January 2011. [I-D.ietf-pcn-cl-edge-behaviour] Charny, A., Huang, F., Karagiannis, G., Menth, M., and T. Taylor, "PCN Boundary Node Behaviour for the Controlled Load (CL) Mode of Operation", draft-ietf-pcn-cl-edge-behaviour-08 (work in progress), December 2010. Menth & Geib Expires September 1, 2011 [Page 6] Internet-Draft AC Using PCN-Marked Signaling February 2011 [I-D.ietf-pcn-psdm-encoding] Menth, M., Babiarz, J., Moncaster, T., and B. Briscoe, "PCN Encoding for Packet-Specific Dual Marking (PSDM Encoding)", draft-ietf-pcn-psdm-encoding-01 (work in progress), March 2010. [I-D.ietf-pcn-sm-edge-behaviour] Charny, A., Karagiannis, G., Menth, M., and T. Taylor, "PCN Boundary Node Behaviour for the Single Marking (SM) Mode of Operation", draft-ietf-pcn-sm-edge-behaviour-05 (work in progress), December 2010. [I-D.menth-pcn-psdm-deployment] Menth, M., "Deployment Models for PCN-Based Admission Control and Flow Termination Using Packet-Specific Dual Marking (PSDM)", draft-menth-pcn-psdm-deployment-00 (work in progress), October 2008. [Menth08-Sub-8] Menth, M. and F. Lehrieder, "Performance of PCN-Based Admission Control", currently under submission, University of Wuerzburg, Germany, 2011. [Menth09f] Menth, M., Babiarz, J., and P. Eardley, "Pre-Congestion Notification Using Packet-Specific Dual Marking", in Proceedings of the International Workshop on the Network of the Future (Future-Net), IEEE, Dresden, Germany, June 2009. Authors' Addresses Michael Menth University of Tuebingen Department of Computer Science Chair of Communication Networks Sand 13 Tuebingen 72076 Germany Phone: +49 7071 29 70505 Email: menth@informatik.uni-tuebingen.de Menth & Geib Expires September 1, 2011 [Page 7] Internet-Draft AC Using PCN-Marked Signaling February 2011 Ruediger Geib Deutsche Telekom Heinrich-Hertz-Strasse 3-7 Darmstadt 64295 Germany Phone: +49 6151 628 2747 Email: ruediger.geib@telekom.de Menth & Geib Expires September 1, 2011 [Page 8]