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Internet Engineering Task Force (IETF)                    G. KaragiannisRequest for Comments: 6663                          University of TwenteCategory: Informational                                        T. TaylorISSN: 2070-1721                                                   Huawei                                                                 K. Chan                                                              Consultant                                                                M. Menth                                                 University of Tuebingen                                                              P. Eardley                                                                      BT                                                               July 2012Requirements for Signaling of Pre-Congestion Informationin a Diffserv DomainAbstract   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 inRFC 5559.  This memo   describes the requirements for the signaling applied within the PCN-   domain: (1) PCN-feedback-information is carried from the PCN-egress-   node to the Decision Point; (2) the Decision Point may ask the PCN-   ingress-node to measure, and report back, the rate of sent PCN-   traffic between that PCN-ingress-node and PCN-egress-node.  The   Decision Point may be either collocated with the PCN-ingress-node or   a centralized node (in the first case, (2) is not required).  The   signaling requirements pertain in particular to two edge behaviors,   Controlled Load (CL) and Single Marking (SM).Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6663.Karagiannis, et al.           Informational                     [Page 1]

RFC 6663               PCN Signaling Requirements              July 2012Copyright Notice   Copyright (c) 2012 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (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 Contents1. Introduction ....................................................21.1. Requirements Language ......................................3   2. Signaling Requirements for Messages from the PCN-Egress-Nodes      to Decision Point(s) ............................................3   3. Signaling Requirements for Messages between Decision Point(s)      and PCN-Ingress-Nodes ...........................................54. Security Considerations .........................................55. Acknowledgments .................................................66. References ......................................................66.1. Normative References .......................................66.2. Informative References .....................................61.  Introduction   The main objective of Pre-Congestion Notification (PCN) is to support   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 and flow termination.  Admission control is   used to decide whether to admit or block a new flow request, while   flow termination is used in abnormal circumstances to decide whether   to terminate some of the existing flows.  To support these two   features, the overall rate of PCN-traffic is metered on every link in   the domain, and PCN-packets are appropriately marked 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 "pre-congestion"   notification).  The PCN-egress-nodes measure the rates of differently   marked PCN traffic in periodic intervals and report these rates to   the Decision Points for admission control and flow termination; the   Decision Points use these rates to make decisions.  The Decision   Points may be collocated with the PCN-ingress-nodes, or theirKaragiannis, et al.           Informational                     [Page 2]

RFC 6663               PCN Signaling Requirements              July 2012   function may be implemented in a centralized node.  For more details   see [RFC5559], [RFC6661], and [RFC6662].   This memo specifies the requirements on signaling protocols:   o  to carry reports from a PCN-egress-node to the Decision Point,   o  to carry requests, from the Decision Point to a PCN-ingress-node,      that trigger the PCN-ingress-node to measure the PCN-sent-rate,   o  to carry reports, from a PCN-ingress-node to the Decision Point.   The latter two messages are only needed if the Decision Point and   PCN-ingress-node are not collocated.1.1.  Requirements Language   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 inRFC 2119 [RFC2119].2.  Signaling Requirements for Messages from the PCN-Egress-Nodes to    Decision Point(s)   The PCN-egress-node measures per ingress-egress-aggregate the rates   of differently marked PCN-traffic in regular intervals.  The   measurement intervals are recommended to take a fixed value between   100 ms and 500 ms; see [RFC6661] and [RFC6662].  At the end of each   measurement interval, the PCN-egress-node calculates the congestion-   level-estimate (CLE) based on these quantities.   The PCN-egress-node MAY be configured to record a set of identifiers   of PCN-flows for which it received excess-traffic-marked packets   during the last measurement interval.  The latter may be useful to   perform flow termination in networks with multipath routing.   At the end of each measurement interval, or less frequently if   "optional report suppression" is activated (see [RFC6661] and   [RFC6662]), the PCN-egress-node sends a report to the Decision Point.   For the SM edge behavior, the report MUST contain:   o  the identifier of the PCN-ingress-node and the identifier of the      PCN-egress-node (typically their IP addresses); together they      specify the ingress-egress-aggregate to which the report refers,   o  the rate of not-marked PCN-traffic (NM-rate) in octets/second, and   o  the rate of PCN-marked traffic (PM-rate) in octets/second.   For the CL edge behavior, the report MUST contain:   o  the identifier of the PCN-ingress-node and the identifier of the      PCN-egress-node (typically their IP addresses); together they      specify the ingress-egress-aggregate to which the report refers,Karagiannis, et al.           Informational                     [Page 3]

RFC 6663               PCN Signaling Requirements              July 2012   o  the rate of not-marked PCN-traffic (NM-rate) in octets/second,   o  the rate of threshold-marked PCN traffic (ThM-rate) in      octets/second, and   o  the rate of excess-traffic-marked traffic (ETM-rate) in      octets/second.   The number format and the rate units used by the signaling protocol   will limit the maximum rate that PCN can use.  If signaling space is   tight, it might be reasonable to impose a limit, but any such limit   may impose unnecessary constraints in the future.   The signaling report can either be sent directly to the Decision   Point or it can "piggy-back", i.e., be included within some other   message that passes through the PCN-egress-node and then reaches the   Decision Point.   As described in [RFC6661], PCN reports from the PCN-egress-node to   the Decision Point may contain flow identifiers for individual flows   within an ingress-egress-aggregate that have recently experienced   excess-marking.  Hence, the PCN report messages used by the PCN CL   edge behavior MUST be capable of carrying sequences of octet strings   constituting such identifiers.   Signaling messages SHOULD have a higher priority and a lower drop   precedence than PCN-packets (see [RFC5559]) in order to deliver them   quickly and to prevent them from being dropped in case of overload.   The load generated by the signaling protocol SHOULD be minimized.  We   give three methods that may help to achieve that goal:   1.  piggy-backing the reports by the PCN-egress-nodes to the Decision      Point(s) onto other signaling messages that are already in place,   2.  reducing the amount of reports to be sent by optional report      suppression, or   3.  combining reports for different ingress-egress-aggregates in a      single message (if they are for the same Decision Point).   As PCN reports are sent regularly, additional reliability mechanisms   are not needed.  This also holds in the presence of optional report   suppression, as reports are sent periodically if actions by the   Decision Point(s) are needed; see [RFC6661] and [RFC6662].Karagiannis, et al.           Informational                     [Page 4]

RFC 6663               PCN Signaling Requirements              July 20123.  Signaling Requirements for Messages between Decision Point(s) and    PCN-Ingress-Nodes   Through request-response signaling between the Decision Point and   PCN-ingress-node, the Decision Point requests and in response the   PCN-ingress-node measures and reports the PCN-sent-rate for a   specific ingress-egress-aggregate.  Signaling is needed only if the   Decision Point and PCN-ingress-node are not collocated.   The request MUST contain:   o  the identifier of the PCN-ingress-node and the identifier of the      PCN-egress-node; together they determine the ingress-egress-      aggregate for which the PCN-sent-rate is requested, and   o  the identifier of the Decision Point that requests the PCN-sent-      rate.   The report MUST contain:   o  the PCN-sent-rate in octets/second, and   o  the identifier of the PCN-ingress-node and the identifier of the      PCN-egress-node.   The request MUST be addressed to the PCN-ingress-node, and the report   MUST be addressed to the Decision Point that requested it.   Because they are sent only when flow termination is needed (which is   an urgent action), the request and the report SHOULD be sent with   high priority, with a lower drop precedence than PCN-packets, and in   a reliable manner.   Note that a complete system description for a PCN-domain with   centralized Decision Point includes the signaling from Decision Point   to the PCN-ingress-nodes to control flow admission and termination.   However, this is a known problem (with solutions provided in   [RFC3084] and [RFC5431], for example), and it lies outside the scope   of the present document.4.  Security Considerations   [RFC5559] provides a general description of the security   considerations for PCN.  This memo relies on the security-related   requirements of the PCN signaling, provided in [RFC5559].  In   particular, the signaling between the PCN-boundary-nodes must be   protected from attacks.  For example, the recipient needs to validate   that the message is indeed from the node that claims to have sent it.   Possible measures include digest authentication and protection   against replay and man-in-the-middle attacks.Karagiannis, et al.           Informational                     [Page 5]

RFC 6663               PCN Signaling Requirements              July 2012   Specifically for the generic aggregate RSVP protocol, additional   protection methods against security attacks are described in   [RFC4860].5.  Acknowledgments   We would like to acknowledge the members of the PCN working group for   the discussions that produced the contents of this memo.6.  References6.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC5559]  Eardley, P., Ed., "Pre-Congestion Notification (PCN)              Architecture",RFC 5559, June 2009.   [RFC6661]  Charny, A., Huang, F., Karagiannis, G., Twente, U., Menth,              M., and T. Taylor, Ed., "Pre-Congestion Notification (PCN)              Boundary-Node Behaviour for the Controlled Load (CL) Mode              of Operation",RFC 6661, July 2012.   [RFC6662]  Charny, A., Zhang, J., Karagiannis, G., Twente, U., Menth,              M., and T. Taylor, Ed., "Pre-Congestion Notification (PCN)              Boundary-Node Behaviour for the Single Marking (SM) Mode              of Operation",RFC 6662, July 2012.6.2.  Informative References   [RFC3084]  Chan, K., Seligson, J., Durham, D., Gai, S., McCloghrie,              K., Herzog, S., Reichmeyer, F., Yavatkar, R., and A.              Smith, "COPS Usage for Policy Provisioning (COPS-PR)",RFC3084, March 2001.   [RFC4860]  Le Faucheur, F., Davie, B., Bose, P., Christou, C., and M.              Davenport, "Generic Aggregate Resource ReSerVation              Protocol (RSVP) Reservations",RFC 4860, May 2007.   [RFC5431]  Sun, D., "Diameter ITU-T Rw Policy Enforcement Interface              Application",RFC 5431, March 2009.Karagiannis, et al.           Informational                     [Page 6]

RFC 6663               PCN Signaling Requirements              July 2012Authors' Addresses   Georgios Karagiannis   University of Twente   P.O. Box 217   7500 AE Enschede,   The Netherlands   EMail: g.karagiannis@utwente.nl   Tom Taylor   Huawei Technologies   Ottawa   Canada   EMail: tom.taylor.stds@gmail.com   Kwok Ho Chan   Consultant   EMail: khchan.work@gmail.com   Michael Menth   University of Tuebingen   Sand 13   72076 Tuebingen   Germany   Phone: +49-7071-2970505   EMail: menth@uni-tuebingen.de   Philip Eardley   BT   B54/77, Sirius House Adastral Park Martlesham Heath   Ipswich, Suffolk  IP5 3RE   United Kingdom   EMail: philip.eardley@bt.comKaragiannis, et al.           Informational                     [Page 7]