Internet Engineering Task Force A. Charny Internet-Draft Cisco Systems Intended status: Experimental F. Huang Expires: December 24, 2011 Huawei Technologies G. Karagiannis U. Twente M. Menth University of Tuebingen T. Taylor, Ed. Huawei Technologies June 22, 2011 PCN Boundary Node Behaviour for the Controlled Load (CL) Mode of Operation draft-ietf-pcn-cl-edge-behaviour-09 Abstract Pre-congestion notification (PCN) is a means for protecting the quality of service for inelastic traffic admitted to a Diffserv domain. The overall PCN architecture is described in RFC 5559. This memo is one of a series describing possible boundary node behaviours for a PCN-domain. The behaviour described here is that for a form of measurement-based load control using three PCN marking states, not- marked, threshold-marked, and excess-traffic-marked. This behaviour is known informally as the Controlled Load (CL) PCN-boundary-node behaviour. 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 December 24, 2011. Copyright Notice Charny, et al. Expires December 24, 2011 [Page 1] Internet-Draft PCN CL Boundary Node Behaviour June 2011 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 (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. Charny, et al. Expires December 24, 2011 [Page 2] Internet-Draft PCN CL Boundary Node Behaviour June 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. [CL-Specific] Assumed Core Network Behaviour for CL . . . . . 8 3. Node Behaviours . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Behaviour of the PCN-Egress-Node . . . . . . . . . . . . . 9 3.2.1. Data Collection . . . . . . . . . . . . . . . . . . . 9 3.2.2. Reporting the PCN Data . . . . . . . . . . . . . . . . 10 3.2.3. Optional Report Suppression . . . . . . . . . . . . . 10 3.3. Behaviour at the Decision Point . . . . . . . . . . . . . 11 3.3.1. Flow Admission . . . . . . . . . . . . . . . . . . . . 11 3.3.2. Flow Termination . . . . . . . . . . . . . . . . . . . 12 3.3.3. Decision Point Action For Missing PCN-Boundary-Node Reports . . . . . . . . . . . . . . 13 3.4. Behaviour of the Ingress Node . . . . . . . . . . . . . . 14 3.5. Summary of Timers and Associated Configurable Durations . 15 3.5.1. Recommended Values For the Configurable Durations . . 16 4. Identifying Ingress and Egress Nodes For PCN Traffic . . . . . 17 5. Specification of Diffserv Per-Domain Behaviour . . . . . . . . 17 5.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 17 5.2. Technical Specification . . . . . . . . . . . . . . . . . 18 5.2.1. Classification and Traffic Conditioning . . . . . . . 18 5.2.2. PHB Configuration . . . . . . . . . . . . . . . . . . 19 5.3. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 19 5.4. Parameters . . . . . . . . . . . . . . . . . . . . . . . . 19 5.5. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 20 5.6. Example Uses . . . . . . . . . . . . . . . . . . . . . . . 21 5.7. Environmental Concerns . . . . . . . . . . . . . . . . . . 21 5.8. Security Considerations . . . . . . . . . . . . . . . . . 21 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 9.1. Normative References . . . . . . . . . . . . . . . . . . . 22 9.2. Informative References . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 Charny, et al. Expires December 24, 2011 [Page 3] Internet-Draft PCN CL Boundary Node Behaviour June 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 (in abnormal circumstances) flow termination to decide whether to terminate some of the existing flows. To achieve this, the overall rate of PCN-traffic is metered on every link in the PCN- 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 PCN-boundary-nodes about incipient overloads before any congestion occurs (hence the "pre" part of "pre-congestion notification"). The level of marking allows decisions to be made about whether to admit or terminate PCN- flows. For more details see [RFC5559]. Section 3 of this document specifies a detailed set of algorithms and procedures used to implement the PCN mechanisms for the CL mode of operation. Since the algorithms depend on specific metering and marking behaviour at the interior nodes, it is also necessary to specify the assumptions made about PCN-interior-node behaviour (Section 2). Finally, because PCN uses DSCP values to carry its markings, a specification of PCN-boundary-node behaviour MUST include the per domain behaviour (PDB) template specified in [RFC3086], filled out with the appropriate content (Section 5). [RFC EDITOR'S NOTE: you may choose to delete the following paragraph and the "[CL-specific]" tags throughout this document when publishing it, since they are present primarily to aid reviewers. RFCyyyy is the published version of draft-ietf-pcn-sm-edge-behaviour.] A companion document [RFCyyyy] specifies the Single Marking (SM) PCN- boundary-node behaviour. This document and [RFCyyyy] have a great deal of text in common. To simplify the task of the reader, the text in the present document that is specific to the CL PCN-boundary-node behaviour is preceded by the phrase: "[CL-specific]". A similar distinction for SM-specific text is made in [RFCyyyy]. 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]. This document uses the following terms defined in Section 2 of [RFC5559]: Charny, et al. Expires December 24, 2011 [Page 4] Internet-Draft PCN CL Boundary Node Behaviour June 2011 o PCN-domain; o PCN-ingress-node; o PCN-egress-node; o PCN-interior-node; o PCN-boundary-node; o PCN-flow; o ingress-egress-aggregate (IEA); o [CL-specific] PCN-threshold-rate; o PCN-excess-rate; o PCN-admissible-rate; o PCN-supportable-rate; o PCN-marked; o [CL-specific] threshold-marked; o excess-traffic-marked. It also uses the terms PCN-traffic and PCN-packet, for which the definition is repeated from [RFC5559] because of their importance to the understanding of the text that follows: PCN-traffic, PCN-packets, PCN-BA A PCN-domain carries traffic of different Diffserv behaviour aggregates (BAs) [RFC2474]. The PCN-BA uses the PCN mechanisms to carry PCN-traffic, and the corresponding packets are PCN-packets. The same network will carry traffic of other Diffserv BAs. The PCN-BA is distinguished by a combination of the Diffserv codepoint and the ECN field. This document uses the following terms from [RFC5670]: o [CL-specific] threshold-meter; o excess-traffic-meter. To complete the list of borrowed terms, this document reuses the following terms and abbreviations defined in Section 3 of [RFC5696]: Charny, et al. Expires December 24, 2011 [Page 5] Internet-Draft PCN CL Boundary Node Behaviour June 2011 o not-PCN codepoint; o Not-marked (NM) codepoint; o PCN-marked (PM) codepoint; o [CL-specific] Experimental (EXP) codepoint. This document defines the following additional terms: Decision Point The node that makes the decision about which flows to admit and to terminate. In a given network deployment, this can be the PCN- ingress-node or a centralized control node. In either case, the PCN-ingress-node is the point where the decisions are enforced. NM-rate The rate of not-marked PCN-traffic received at a PCN-egress-node for a given ingress-egress-aggregate in octets per second. For further details see Section 3.2.1. [CL-specific] ThM-rate The rate of threshold-marked PCN-traffic received at a PCN-egress- node for a given ingress-egress-aggregate in octets per second. For further details see Section 3.2.1. ETM-rate The rate of excess-traffic-marked PCN-traffic received at a PCN- egress-node for a given ingress-egress-aggregate in octets per second. For further details see Section 3.2.1. PCN-sent-rate The rate of PCN-traffic received at a PCN-ingress-node and destined for a given ingress-egress-aggregate in octets per second. For further details see Section 3.4. Congestion level estimate (CLE) The ratio of PCN-marked to total PCN-traffic (measured in octets) received for a given ingress-egress-aggregate during a given measurement period. The CLE is used to derive the PCN-admission- state (Section 3.3.1) and is also used by the report suppression procedure (Section 3.2.3) if report suppression is activated. PCN-admission-state The state ("admit" or "block") derived by the Decision Point for a given ingress-egress-aggregate based on PCN packet marking statistics. The Decision Point decides to admit or block new flows offered to the aggregate based on the current value of the Charny, et al. Expires December 24, 2011 [Page 6] Internet-Draft PCN CL Boundary Node Behaviour June 2011 PCN-admission-state. For further details see Section 3.3.1. Sustainable aggregate rate (SAR) The estimated maximum rate of PCN-traffic that can be carried in a given ingress-egress-aggregate at a given moment without risking degradation of quality of service for the admitted flows. The intention is that if the PCN-sent-rate of every ingress-egress- aggregate passing through a given link is limited to its sustainable aggregate rate, the total rate of PCN-traffic flowing through the link will be limited to the PCN-supportable-rate for that link. An estimate of the sustainable aggregate rate for a given ingress-egress-aggregate is derived as part of the flow termination procedure, and is used to determine how much PCN- traffic needs to be terminated. For further details see Section 3.3.2. CLE-reporting-threshold A configurable value against which the CLE is compared as part of the report suppression procedure. For further details, see Section 3.2.3. CLE-limit A configurable value against which the CLE is compared to determine the PCN-admission-state for a given ingress-egress- aggregate. For further details, see Section 3.3.1. T-meas A configurable time interval that defines the measurement period over which the PCN-egress-node collects statistics relating to PCN-traffic marking. At the end of the interval the PCN-egress- node calculates the values NM-rate, [CL-specific] ThM-rate, and ETM-rate as defined and sends a report to the Decision Point, subject to the operation of the report suppression feature. For further details see Section 3.2. T-maxsuppress A configurable time interval after which the PCN-egress-node MUST send a report to the Decision Point for a given ingress-egress- aggregate regardless of the most recent values of the CLE. This mechanism provides the Decision Point with a periodic confirmation of liveness when report suppression is activated. For further details, see Section 3.2.3. T-fail A configurable interval after which the Decision Point concludes that communication from a given PCN-egress-node has failed if it has received no reports from the PCN-egress-node during that interval. For further details see Section 3.3.3. Charny, et al. Expires December 24, 2011 [Page 7] Internet-Draft PCN CL Boundary Node Behaviour June 2011 2. [CL-Specific] Assumed Core Network Behaviour for CL This section describes the assumed behaviour for PCN-interior-nodes in the PCN-domain. The CL mode of operation assumes that: o PCN-interior-nodes perform both threshold-marking and excess- traffic-marking of PCN-packets, according to the rules specified in [RFC5670]; o excess-traffic-marking of PCN-packets uses the PCN-Marked (PM) codepoint defined in [RFC5696]; o threshold-marking of PCN-packets uses the EXP codepoint defined in [RFC5696]; o the PCN-domain satisfies the conditions specified in [RFC5696]; o on each link the reference rate for the threshold-meter is configured to be equal to the PCN-admissible-rate for the link; o on each link the reference rate for the excess-traffic-meter is configured to be equal to the PCN-supportable-rate for the link; o the set of valid codepoint transitions is as shown in Section 4.2 of [RFC5696]. 3. Node Behaviours 3.1. Overview This section describes the behaviour of the PCN-ingress-node, PCN- egress-node, and the Decision Point (which MAY be collocated with the PCN-ingress-node). The PCN-egress-node collects the rates of not-marked, [CL-specific] threshold-marked, and excess-traffic-marked PCN-traffic for each ingress-egress-aggregate and reports them to the Decision Point. [CL-specific] It MAY also identify and report PCN-flows that have experienced excess-traffic-marking. For a detailed description, see Section 3.2. The PCN-ingress-node enforces flow admission and termination decisions. It also reports the rate of PCN-traffic sent to a given ingress-egress-aggregate when requested by the Decision Point. For details, see Section 3.4. Finally, the Decision Point makes flow admission decisions and Charny, et al. Expires December 24, 2011 [Page 8] Internet-Draft PCN CL Boundary Node Behaviour June 2011 selects flows to terminate based on the information provided by the PCN-ingress-node and PCN-egress-node for a given ingress-egress- aggregate. For details, see Section 3.3. 3.2. Behaviour of the PCN-Egress-Node 3.2.1. Data Collection The PCN-egress-node MUST meter the PCN-traffic it receives in order to calculate the following rates for each ingress-egress-aggregate passing through it. These rates SHOULD be calculated at the end of each measurement period based on the PCN-traffic observed during that measurement period. The duration of a measurement period is equal to the configurable value T-meas. For further information see Section 3.5. o NM-rate: octets per second of PCN-traffic in PCN-packets that are not-marked (i.e., marked with the NM codepoint); o [CL-specific] ThM-rate: octets per second of PCN-traffic in PCN- packets that are threshold-marked (i.e., marked with the EXP codepoint); o ETM-rate: octets per second of PCN-traffic in PCN-packets that are excess-traffic-marked (i.e., marked with the PM codepoint). Informative note: metering the PCN-traffic continuously and using equal-length measurement intervals minimizes the statistical variance introduced by the measurement process itself. On the other hand, the operation of PCN is not affected if the starting and ending times of the measurement intervals for different ingress-egress-aggregates are different. [CL-specific] As a configurable option, the PCN-egress-node MAY record flow identifiers of the PCN-flows for which excess-traffic- marked packets have been observed during this measurement interval. If this set is large (e.g., more than 20 flows), the PCN-egress-node MAY record only the most recently excess-traffic-marked PCN-flow identifiers rather than the complete set. These can be used by the Decision Point when it selects flows for termination. In networks using multipath routing it is possible that congestion is not occurring on all paths carrying a given ingress-egress-aggregate. Assuming that specific PCN-flows are routed via specific paths, identifying the PCN-flows that are experiencing excess-traffic-marking helps to avoid termination of PCN-flows not contributing to congestion. Charny, et al. Expires December 24, 2011 [Page 9] Internet-Draft PCN CL Boundary Node Behaviour June 2011 3.2.2. Reporting the PCN Data Unless the report suppression option described in Section 3.2.3 is activated, the PCN-egress-node MUST report the latest values of NM- rate, [CL-specific] ThM-rate, and ETM-rate to the Decision Point each time that it calculates them. [CL-specific] If the PCN-egress-node recorded a set of flow identifiers of PCN-flows for which excess-traffic-marking was observed in the most recent measurement interval, then it MUST also include these identifiers in the report. 3.2.3. Optional Report Suppression Report suppression MUST be provided as a configurable option, along with two configurable parameters, the CLE-reporting-threshold and the maximum report suppression interval T-maxsuppress. The default value of the CLE-reporting-threshold is zero. The CLE-reporting-threshold MUST NOT exceed the CLE-limit configured at the Decision Point. For further information on T-maxsuppress see Section 3.5. If the report suppression option is enabled, the PCN-egress-node MUST apply the following procedure to decide whether to send a report to the Decision Point, rather than sending a report automatically at the end of each measurement interval. 1. As well as the quantities NM-rate, [CLE-specific] ThM-rate, and ETM-rate, the PCN-egress-node MUST calculate the congestion level estimate (CLE) for each measurement interval. The CLE is computed as: [CL-specific] CLE = (ThM-rate + ETM-rate) / (NM-rate + ThM-rate + ETM-rate) if any PCN-traffic was observed, or CLE = 0 if all the rates are zero. 2. If the CLE calculated for the latest measurement interval is greater than the CLE-reporting-threshold and/or the CLE calculated for the immediately previous interval was greater than the CLE-reporting-threshold, then the PCN-egress-node MUST send a report to the Decision Point. The contents of the report are described below. The reason for taking into account the CLE of the previous interval is to ensure that the Decision Point gets immediate feedback if the CLE has dropped below CLE-reporting-threshold. This is essential if the Decision Point is running the flow Charny, et al. Expires December 24, 2011 [Page 10] Internet-Draft PCN CL Boundary Node Behaviour June 2011 termination procedure and observing whether (further) flow termination is needed. See Section 3.3.2. 3. If an interval T-maxsuppress has elapsed since the last report was sent to the Decision Point, then the PCN-egress-node MUST send a report to the Decision Point regardless of the CLE value. 4. If neither of the preceding conditions holds, the PCN-egress-node MUST NOT send a report for the latest measurement interval. Each report sent to the Decision Point when report suppression has been activated MUST contain the values of NM-rate, [CL-specific] ThM- rate, ETM-rate, and CLE that were calculated for the most recent measurement interval. [CL-specific] If the PCN-egress-node recorded a set of flow identifiers of PCN-flows for which excess-traffic- marking was observed in the most recent measurement interval, then it MUST also include these identifiers in the report. The above procedure ensures that at least one report is sent per interval (T-maxsuppress + T-meas). This demonstrates to the Decision Point that both the PCN-egress-node and the communication path between that node and the Decision Point are in operation. 3.3. Behaviour at the Decision Point Operators can choose to use PCN procedures just for flow admission, or just for flow termination, or for both. A compliant Decision Point MUST implement both mechanisms, but configurable options MUST be provided to activate or deactivate PCN-based flow admission and flow termination independently of each other at a given Decision Point. If PCN-based flow termination is enabled but PCN-based flow admission is not, flow termination operates as specified in this document. Logically, some other system of flow admission control is in operation, but the description of such a system is out of scope of this document and depends on local arrangements. 3.3.1. Flow Admission The Decision Point determines the PCN-admission-state for a given ingress-egress-aggregate each time it receives a report from the egress node. It makes this determination on the basis of the congestion level estimate (CLE). If the CLE is provided in the egress node report, the Decision Point SHOULD use the reported value. If the CLE was not provided in the report, the Decision Point MUST calculate it based on the other values provided in the report, using Charny, et al. Expires December 24, 2011 [Page 11] Internet-Draft PCN CL Boundary Node Behaviour June 2011 the formula: [CL-specific] CLE = (ThM-rate + ETM-rate) / (NM-rate + ThM-rate + ETM-rate) if any PCN-traffic was observed, or CLE = 0 if all the rates are zero. The Decision Point MUST compare the reported or calculated CLE to a configurable value, the CLE-limit. If the CLE is less than the CLE- limit, the PCN-admission-state for that aggregate MUST be set to "admit"; otherwise it MUST be set to "block". [CL-specific] The outcome of the comparison is not very sensitive to the value of the CLE-limit in practice, because when threshold- marking occurs it tends to persist long enough that threshold- marked traffic becomes a large proportion of the received traffic in a given interval. If the PCN-admission-state for a given ingress-egress-aggregate is "admit", the Decision Point SHOULD allow new flows to be admitted to that aggregate. If the PCN-admission-state for a given ingress- egress-aggregate is "block", the Decision Point SHOULD NOT allow new flows to be admitted to that aggregate. These actions MAY be modified by policy in specific cases, but such policy intervention risks defeating the purpose of using PCN. 3.3.2. Flow Termination [CL-specific] When the report from the PCN-egress-node includes a non-zero value of the ETM-rate for some ingress-egress-aggregate, the Decision Point MUST request the PCN-ingress-node to provide an estimate of the rate (PCN-sent-rate) at which the PCN-ingress-node is receiving PCN-traffic that is destined for the given ingress-egress- aggregate. If the Decision Point is collocated with the PCN-ingress-node, the request and response are internal operations. The Decision Point MUST then wait, for both the requested rate from the PCN-ingress-node and the next report from the PCN-egress-node for the ingress-egress-aggregate concerned. If this next egress node report also includes a non-zero value for the ETM-rate, the Decision Point MUST determine the amount of PCN-traffic to terminate using the following steps: 1. [CL-specific] The sustainable aggregate rate (SAR) for the given ingress-egress-aggregate is estimated by the sum: Charny, et al. Expires December 24, 2011 [Page 12] Internet-Draft PCN CL Boundary Node Behaviour June 2011 SAR = NM-rate + ThM-rate for the latest reported interval. 2. The amount of traffic to be terminated is the difference: PCN-sent-rate - SAR, where PCN-sent-rate is the value provided by the PCN-ingress- node. See Section 3.3.3 for a discussion of appropriate actions if the Decision Point fails to receive a timely response to its request for the PCN-sent-rate. If the difference calculated in the second step is positive, the Decision Point SHOULD select PCN-flows to terminate, until it determines that the PCN-traffic admission rate will no longer be greater than the estimated sustainable aggregate rate. If the Decision Point knows the bandwidth required by individual PCN-flows (e.g., from resource signalling used to establish the flows), it MAY choose to complete its selection of PCN-flows to terminate in a single round of decisions. Alternatively, the Decision Point MAY spread flow termination over multiple rounds to avoid over-termination. If this is done, it is RECOMMENDED that enough time elapse between successive rounds of termination to allow the effects of previous rounds to be reflected in the measurements upon which the termination decisions are based. (See [IEEE-Satoh] and sections 4.2 and 4.3 of [MeLe10].) In general, the selection of flows for termination MAY be guided by policy. [CL-specific] If the egress node has supplied a list of identifiers of PCN-flows that experienced excess-traffic-marking (Section 3.2), the Decision Point SHOULD first consider terminating PCN-flows in that list. 3.3.3. Decision Point Action For Missing PCN-Boundary-Node Reports The Decision Point SHOULD start a timer t-recvFail when it receives a report from the PCN-egress-node. t-recvFail is reset each time a new report is received from the PCN-egress-node. t-recvFail expires if it reaches the value T-fail. T-fail is calculated according to the following logic: a. T-fail = the configurable duration T-crit, if report suppression is not deployed; Charny, et al. Expires December 24, 2011 [Page 13] Internet-Draft PCN CL Boundary Node Behaviour June 2011 b. T-fail = T-crit also if report suppression is deployed and the last report received from the PCN-egress-node contained a CLE value greater than CLE-reporting-threshold (Section 3.2.3); c. T-fail = 3 * T-maxsuppress (Section 3.2.3) if report suppression is deployed and the last report received from the PCN-egress-node contained a CLE value less than or equal to CLE-reporting- threshold. If timer t-recvFail expires for a given PCN-egress-node, the Decision Point SHOULD raise an alarm to management. A Decision Point collocated with a PCN-ingress-node SHOULD cease to admit PCN-flows to the ingress-egress-aggregate associated with the given PCN-egress- node, until it again receives a report from that node. A centralized Decision Point MAY cease to admit PCN-flows to all ingress-egress- aggregates destined to the PCN-egress-node concerned, until it again receives a report from that node. A centralized Decision Point SHOULD start a timer t-sndFail when it sends a request for the estimated value of PCN-sent-rate to a given PCN-ingress-node. If the Decision Point fails to receive a response from the PCN-ingress-node before t-sndFail reaches the configurable value T-crit, the Decision Point SHOULD repeat the request but MAY also use ETM-rate as an estimate of the amount of traffic to be terminated in place of the quantity PCN-sent-rate - SAR specified in Section 3.3.2. Because this will over-estimate the amount of traffic to be terminated due to dropping of PCN-packets by interior nodes, the Decision Point SHOULD use multiple rounds of termination under these circumstances. If the second request to the PCN-ingress-node also fails, the Decision Point SHOULD raise an alarm to management. The use of T-crit is an approximation. A more precise limit would be of the order of two round-trip times, plus an allowance for processing at each end, plus an allowance for variance in these values. See Section 3.5 for suggested values of the configurable durations T-crit and T-maxsuppress. 3.4. Behaviour of the Ingress Node The PCN-ingress-node MUST provide the estimated current rate of PCN- traffic received at that node and destined for a given ingress- egress-aggregate in octets per second (the PCN-sent-rate) when the Charny, et al. Expires December 24, 2011 [Page 14] Internet-Draft PCN CL Boundary Node Behaviour June 2011 Decision Point requests it. The way this rate estimate is derived is a matter of implementation. For example, the rate that the PCN-ingress-node supplies MAY be based on a quick sample taken at the time the information is required. 3.5. Summary of Timers and Associated Configurable Durations Here is a summary of the timers used in the procedures just described: t-meas Where used: PCN-egress-node. Used in procedure: data collection (Section 3.2.1). Incidence: one per ingress-egress-aggregate. Reset: immediately on expiry. Expiry: when it reaches the configurable duration T-meas. Action on expiry: calculate NM-rate, [CL-specific] ThM-rate, and ETM-rate and proceed to the applicable reporting procedure (Section 3.2.2 or Section 3.2.3). t-maxsuppress Where used: PCN-egress-node. Used in procedure: report suppression (Section 3.2.3). Incidence: one per ingress-egress-aggregate. Reset: when the next report is sent after expiry. Expiry: when it reaches the configurable duration T-maxsuppress. Action on expiry: send a report to the Decision Point the next time the reporting procedure (Section 3.2.3) is invoked, regardless of the value of CLE. Charny, et al. Expires December 24, 2011 [Page 15] Internet-Draft PCN CL Boundary Node Behaviour June 2011 t-recvFail Where used: Decision Point. Used in procedure: failure detection (Section 3.3.3). Incidence: one per ingress-egress-aggregate. Reset: when a report is received for the ingress-egress- aggregate. Expiry: when it reaches the calculated duration T-fail. As described in Section 3.3.3, T-fail is either equal to the configured duration T-crit or to the calculated value 3 * T-maxsuppress, where T-maxsuppress is a configured duration. Action on expiry: raise an alarm to management, and possibly other actions. t-sndFail Where used: centralized Decision Point. Used in procedure: failure detection (Section 3.3.3). Incidence: only as required, one per outstanding request to a PCN-ingress-node. Started: when a request for the value of PCN-sent-traffic for a given ingress-egress-aggregate is sent to the PCN-ingress-node. Terminated without action: when a response is received before expiry. Expiry: when it reaches the configured duration T-crit. Action on expiry: repeat the request, but use an approximation for the estimate of amount of traffic to terminate. After two failures, raise an alarm to management and stop repeating the request. 3.5.1. Recommended Values For the Configurable Durations The timers just described depend on three configurable durations, T-meas, T-maxsuppress, and T-crit. The recommendations given below for the values of these durations are all related to the intended PCN reaction time of 1 to 3 seconds. However, they are based on judgement rather than operational experience or mathematical Charny, et al. Expires December 24, 2011 [Page 16] Internet-Draft PCN CL Boundary Node Behaviour June 2011 derivation. The value of T-meas is RECOMMENDED to be of the order of 100 to 500 ms to provide a reasonable tradeoff between demands on network resources (PCN-egress-node and Decision Point processing, network bandwidth) and the time taken to react to impending congestion. The value of T-maxsuppress is RECOMMENDED to be on the order of 3 to 6 seconds, for similar reasons to those for the choice of T-meas. The value of T-crit SHOULD NOT be less than 3 * T-meas. Otherwise it could cause too many alarms to be raised due to transient conditions in the PCN-egress-node or along the signalling path. A reasonable upper bound on T-crit is in the order of 3 seconds. 4. Identifying Ingress and Egress Nodes For PCN Traffic The operation of PCN depends on the ability of the PCN-ingress-node to identify the ingress-egress-aggregate to which each new PCN-flow belongs and the ability of the egress node to identify the ingress- egress-aggregate to which each received PCN-packet belongs. If the Decision Point is collocated with the PCN-ingress-node, the PCN- egress-node also needs to associate each ingress-egress-aggregate with the address of the PCN-ingress-node to which it sends its reports. The means by which this is done depends on the packet routing technology in use in the network. The procedure to provide the required information is out of scope for this document. 5. Specification of Diffserv Per-Domain Behaviour This section provides the specification required by [RFC3086] for a per-domain behaviour. 5.1. Applicability This section quotes [RFC5559]. The PCN CL boundary node behaviour specified in this document is applicable to inelastic traffic (particularly video and voice) where quality of service for admitted flows is protected primarily by admission control at the ingress to the domain. In exceptional circumstances (e.g., due to rerouting as a result of network failures) already-admitted flows MAY be terminated to protect Charny, et al. Expires December 24, 2011 [Page 17] Internet-Draft PCN CL Boundary Node Behaviour June 2011 the quality of service of the remaining flows. [CL-specific] The performance results in, e.g., [MeLe10], indicate that the CL boundary node behaviour provides better service outcomes under such circumstances than the SM boundary node behaviour described in [RFCyyyy], because CL is less likely to terminate PCN-flows unnecessarily. [RFC EDITOR'S NOTE: please replace RFCyyyy above by the reference to the published version of draft-ietf-pcn-sm-edge-behaviour.] 5.2. Technical Specification 5.2.1. Classification and Traffic Conditioning This section paraphrases the applicable portions of Sections 3.6 and 4.2 of [RFC5559]. Packets at the ingress to the domain are classified as either PCN or non-PCN. Non-PCN packets MAY share the network with PCN packets within the domain. Because the encoding specified in [RFC5696] and used in this document requires the use of the ECN fields, PCN- ingress-nodes MUST prevent ECN-capable traffic that uses the same DSCP as PCN from entering the PCN-domain directly. The PCN-ingress- node can accomplish this in three ways. The choice between these depends on local policy. o ECN-capable traffic MAY be dropped. This policy is NOT RECOMMENDED, since it prevents the proper operation of end-to-end ECN as a means of controlling congestion. o ECN-capable traffic MAY be assigned a different DSCP from PCN traffic. This could mean that it is relegated to a lower-priority behaviour aggregate. o ECN-capable traffic MAY be tunneled across the PCN-domain. If this is done, the PCN-ingress-node MUST mark packets as either not-PCN or PCN-not-marked only after the encapsulation of the packet, including any initial setting of the ECN field, has been completed. PCN packets are further classified as belonging or not belonging to an admitted flow. PCN packets not belonging to an admitted flow are dropped. (This assumes that requests for flow admission are signalled in advance of the arrival of the flows themselves.) Packets belonging to an admitted flow are policed to ensure that they adhere to the rate or flowspec that was negotiated during flow admission. Charny, et al. Expires December 24, 2011 [Page 18] Internet-Draft PCN CL Boundary Node Behaviour June 2011 5.2.2. PHB Configuration The PCN CL boundary node behaviour is a metering and marking behaviour rather than a scheduling behaviour. As a result, while the encoding uses a single DSCP value, that value MAY vary from one deployment to another. The PCN working group suggests using admission control for the following service classes (defined in [RFC4594]): o Telephony (EF) o Real-time interactive (CS4) o Broadcast Video (CS3) o Multimedia Conferencing (AF4) For a fuller discussion, see Section A.1 of Appendix A of [RFC5696]. 5.3. Attributes The purpose of this per-domain behaviour is to achieve low loss and jitter for the target class of traffic. The design requirement for PCN was that recovery from overloads through the use of flow termination SHOULD happen within 1-3 seconds. PCN probably performs better than that. 5.4. Parameters In the list that follows, note that most PCN-ingress-nodes are also PCN-egress-nodes, and vice versa. Furthermore, the PCN-ingress-nodes MAY be collocated with Decision Points. Parameters at the PCN-ingress-node: ----------------------------------- o Filters for distinguishing PCN from non-PCN inbound traffic. o The markings to be applied to PCN-traffic. o Reference rates on each link for the [CL-specific] threshold-meter and the excess-traffic-meter; see Section 2. o The information needed to distinguish PCN-traffic belonging to a given ingress-egress-aggregate. Parameters at the PCN-egress-node: ---------------------------------- Charny, et al. Expires December 24, 2011 [Page 19] Internet-Draft PCN CL Boundary Node Behaviour June 2011 o The measurement interval T-meas. o Activation/deactivation of report suppression and, if report suppression is activated, the values of the CLE-reporting- threshold and T-maxsuppress. o [CL-specific] Activation/deactivation of recording of individual flow identifiers when excess-traffic-marked PCN-traffic is observed. o The information needed to distinguish PCN-traffic belonging to a given ingress-egress-aggregate. o The marking rules for re-marking PCN-traffic leaving the PCN domain. Parameters at each interior node: --------------------------------- o Reference rates on each link for the [CL-specific] threshold-meter and the excess-traffic-meter; see Section 2. o The markings to be applied to PCN-traffic, including the identification of PCN-packets and the encodings to indicate excess-traffic-marking and [CL-specific] threshold-marking. Parameters at the Decision Point: --------------------------------- o Activation/deactivation of PCN-based flow admission. o Activation/deactivation of PCN-based flow termination. o The value of CLE-limit. o The maximum interval T-fail between reports from a given PCN- egress-node, for detecting failure of communications with that node. o The information needed to map each ingress-egress-aggregate to the corresponding PCN-ingress-node and PCN-egress-node. 5.5. Assumptions It is assumed that a specific portion of link capacity has been reserved for PCN-traffic. Charny, et al. Expires December 24, 2011 [Page 20] Internet-Draft PCN CL Boundary Node Behaviour June 2011 5.6. Example Uses The PCN CL behaviour MAY be used to carry real-time traffic, particularly voice and video. 5.7. Environmental Concerns The PCN CL per-domain behaviour can interfere with the use of end-to- end ECN due to reuse of ECN bits for PCN marking. See Appendix B of [RFC5696] for details. 5.8. Security Considerations Please see the security considerations in [RFC5559] as well as those in [RFC2474] and [RFC2475]. 6. Security Considerations [RFC5559] provides a general description of the security considerations for PCN. This memo introduces no new considerations. 7. IANA Considerations This memo includes no request to IANA. 8. Acknowledgements The content of this memo bears a family resemblance to [ID.briscoe-CL]. The authors of that document were Bob Briscoe, Philip Eardley, and Dave Songhurst of BT, Anna Charny and Francois Le Faucheur of Cisco, Jozef Babiarz, Kwok Ho Chan, and Stephen Dudley of Nortel, Giorgios Karagiannis of U. Twente and Ericsson, and Attila Bader and Lars Westberg of Ericsson. Ruediger Geib, Philip Eardley, and Bob Briscoe have helped to shape the present document with their comments. Toby Moncaster gave a careful review to get it into shape for Working Group Last Call. Amongst the authors, Michael Menth deserves special mention for his constant and careful attention to both the technical content of this document and the manner in which it was expressed. 9. References Charny, et al. Expires December 24, 2011 [Page 21] Internet-Draft PCN CL Boundary Node Behaviour June 2011 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 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. [RFC3086] Nichols, K. and B. Carpenter, "Definition of Differentiated Services Per Domain Behaviors and Rules for their Specification", RFC 3086, April 2001. [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. 9.2. Informative References [ID.briscoe-CL] Briscoe, B., "An edge-to-edge Deployment Model for Pre- Congestion Notification: Admission Control over a DiffServ Region (expired Internet Draft)", 2006. [IEEE-Satoh] Satoh, D. and H. Ueno, ""Cause and Countermeasure of Overtermination for PCN-Based Flow Termination", Proceedings of IEEE Symposium on Computers and Communications (ISCC '10), pp. 155-161, Riccione, Italy", June 2010. [MeLe10] Menth, M. and F. Lehrieder, "PCN-Based Measured Rate Termination", Computer Networks Journal (Elsevier) vol. 54, no. 13, pages 2099 - 2116, September 2010. [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration Guidelines for DiffServ Service Classes", RFC 4594, Charny, et al. Expires December 24, 2011 [Page 22] Internet-Draft PCN CL Boundary Node Behaviour June 2011 August 2006. [RFC6040] Briscoe, B., "Tunnelling of Explicit Congestion Notification", RFC 6040, November 2010. [RFCyyyy] Charny, A., Zhang, J., Karagiannis, G., Menth, M., and T. Taylor, "PCN Boundary Node Behaviour for the Single Marking (SM) Mode of Operation (Work in progress)", December 2010. Authors' Addresses Anna Charny Cisco Systems 300 Apollo Drive Chelmsford, MA 01824 USA Email: acharny@cisco.com Fortune Huang Huawei Technologies Section F, Huawei Industrial Base, Bantian Longgang, Shenzhen 518129 P.R. China Phone: +86 15013838060 Email: fqhuang@huawei.com Georgios Karagiannis U. Twente Phone: Email: karagian@cs.utwente.nl Charny, et al. Expires December 24, 2011 [Page 23] Internet-Draft PCN CL Boundary Node Behaviour June 2011 Michael Menth University of Tuebingen Sand 13 Tuebingen D-72076 Germany Phone: +49-7071-2970505 Email: menth@informatik.uni-tuebingen.de Tom Taylor (editor) Huawei Technologies 1852 Lorraine Ave Ottawa, Ontario K1H 6Z8 Canada Phone: +1 613 680 2675 Email: tom111.taylor@bell.net Charny, et al. Expires December 24, 2011 [Page 24]