Congestion and Pre-Congestion                                 B. Briscoe
Notification                                                          BT
Internet-Draft                                              T. Moncaster
Internet-Draft                                                        BT
Intended status: Experimental                             March 08, 2010                                Independent
Expires: September 9, January 13, 2011                                       M. Menth
                                                 University of Wuerzburg
                                                           July 12, 2010

            PCN 3-State

       Encoding Extension 3 PCN-States in the IP header using a single DSCP
                   draft-ietf-pcn-3-in-1-encoding-02
                   draft-ietf-pcn-3-in-1-encoding-03

Abstract

   The objective of Pre-Congestion Notification (PCN) is to protect the
   quality of service (QoS) of inelastic flows within a Diffserv domain.
   The
   On every link in the PCN domain, the overall rate of the PCN-traffic
   is metered on every link in the
   PCN-domain, metered, and PCN-packets are appropriately marked when certain
   configured rates are exceeded.  The level  Egress nodes provide decision points
   with information about the PCN-marks of marking PCN-packets which allows the
   boundary nodes them
   to make take decisions about whether to admit or block a new flow request,
   and (in abnormal circumstances) whether to terminate some of the existing flows, thereby protecting the QoS of
   previously already admitted flows. flows during serious pre-
   congestion.

   This document specifies how such marks PCN-marks are to be encoded into the IP
   header by re-using the Explicit Congestion Notification (ECN)
   codepoints within this controlled
   domain. a PCN-domain.  This encoding builds on the baseline
   encoding of RFC5696 and provides for three different PCN encoding states: Not-marked, Threshold-marked and
   Excess-traffic-marked. marking
   states using a single DSCP: not-marked (NM), threshold-marked (ThM)
   and excess-traffic-marked (ETM).  Hence, it is called the 3-in-1 PCN
   encoding.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 9, 2010. January 13, 2011.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Changes in This Version (to be removed by RFC Editor)  . .  4
   2.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Requirements for and Applicability of 3-in-1 PCN Encoding  . .  5
     3.1.  PCN Requirements . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Requirements Imposed by Baseline Encoding  . . . . . . . .  6
     3.3.  Applicability of 3-in-1 PCN Encoding . . . . . . . . . . .  6
   4.  Definition of 3-in-1 PCN Encoding  . . . . . . . . . . . . . .  7
   5.  Behaviour of a PCN Node Compliant with the 3-in-1 PCN
       Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Backward Compatibility . . . . . . . . . . . . . . . . . . . .  8
     6.1.  Backward Compatibility with Pre-existing PCN
           Implementations  . . . . . . . . . . . . . . . . . . . . .  8
     6.2.  Recommendations for the Use of PCN Encoding Schemes  . . .  9
       6.2.1.  Use of Both Excess-Traffic-Marking and
               Threshold-Marking  . . . . . . . . . . . . . . . . . .  9
       6.2.2.  Unique Use of Excess-Traffic-Marking . . . . . . . . .  9
       6.2.3.  Unique Use of Threshold-Marking  . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   9.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 10
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   11. Comments Solicited . . . . . . . . . . . . . . . . . . . . . . 10
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 11
     12.2. Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

1.  Introduction

   The objective of Pre-Congestion Notification (PCN) [RFC5559] 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. already admitted flows during serious pre-congestion.
   To achieve this, 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 "pre-
   congestion notification").

   The level of

   Two metering and marking allows boundary nodes to make decisions about
   whether to admit or terminate.  This is achieved by functions are proposed in [RFC5670] that are
   configured with reference rates.  Threshold- marking packets
   on interior nodes according to some metering function implemented at
   each node.  Threshold-traffic-marking marks all PCN
   packets once they
   exceed the threshold-traffic-rate their traffic rate on a link while Excess-traffic-
   marking exceeds the configured
   reference rate (PCN-threshold-rate).  Excess-traffic-marking marks
   only those PCN packets that exceed the excess-traffic-
   rate, which is higher than the threshold-traffic-rate [RFC5670].
   These marks are monitored by configured reference rate
   (PCN-excess-rate).  The PCN-excess-rate is typically larger than the egress
   PCN-threshold-rate [RFC5559].  Egress nodes of monitor the PCN domain.

   To fully support these two types PCN-marks of marking, three encoding states
   are needed.
   received PCN-packets and provide information about the PCN-marks to
   decision points which take decisions about flow admission and
   termination on this basis [I-D.ietf-pcn-cl-edge-behaviour],
   [I-D.ietf-pcn-sm-edge-behaviour].

   The baseline encoding described defined in [RFC5696] provides
   for deployment scenarios that only require describes how two PCN encoding
   marking states can be encoded using a single Diffserv codepoint.
   However, to support the application of two different marking
   algorithms in a PCN-domain, for example as required in
   [I-D.ietf-pcn-cl-edge-behaviour], three PCN marking states are
   needed.  This document describes an
   experimental extension to the baseline-encoding baseline
   encoding that adds a third PCN
   encoding marking state in the IP header, still
   using a single Diffserv codepoint.  For brevity it will be  This encoding scheme is called the 3-in-1
   ao˛3-in-1 PCN Encoding.

   General PCN-related terminology is defined in the encodingaoˇ.

   All PCN architecture
   [RFC5559], and terminology specific to packet encoding is defined in
   the schemes require an additional marking state to
   indicate non-PCN traffic.  Therefore, four codepoints are required to
   encode three PCN baseline encoding [RFC5696].  Note that [RFC5696] requires marking states.

   This document only concerns the PCN Working Group to maintain a list of wire protocol encoding for all DSCPs used IP
   headers, whether IPv4 or IPv6.  It makes no changes or
   recommendations concerning algorithms for congestion marking or
   congestion response.  Other documents define the PCN
   experiments. wire protocol
   for other header types.  For example, the MPLS encoding is defined in
   [RFC5129].  Appendix A provides an informative example for a mapping
   between the encodings in IP and in MPLS.

1.1.  Changes in This Version (to be removed by RFC Editor)

   From draft-ietf-pcn-3-in-1-encoding-02 to -03:

      *  Corrected mistakes in introduction and improved overall
         readability.

      *  Added new terminology.

      *  Rewrote a good part of Section 4 and 5 to achieve more clarity.

      *  Added appendix explaining when to use which encoding scheme and
         how to encode them in MPLS shim headers.

      *  Added new co-author.

   From draft-ietf-pcn-3-in-1-encoding-01 to -02:

      *  Corrected mistake in introduction, which wrongly stated that
         the threshold-traffic rate is higher than the excess-traffic
         rate.  Other minor corrections.

      *  Updated acks & refs.

   From draft-ietf-pcn-3-in-1-encoding-00 to -01:

      *  Altered the wording to make sense if
         [I-D.ietf-tsvwg-ecn-tunnel] moves to proposed standard.

      *  References updated

   From draft-briscoe-pcn-3-in-1-encoding-00 to
   draft-ietf-pcn-3-in-1-encoding-00:

      *  Filename changed to draft-ietf-pcn-3-in-1-encoding.

      *  Introduction altered to include new template description of
         PCN.

      *  References updated.

      *  Terminology brought into line with [RFC5670].

      *  Minor corrections.

2.  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 in RFC 2119 [RFC2119].

2.1.  Terminology

   General PCN-related terminology is defined in the PCN architecture
   [RFC5559], and terminology specific to packet encoding is defined in
   the PCN baseline encoding [RFC5696].  Additional terminology is
   defined below.

   PCN encoding:  mapping of PCN marking states to specific codepoints
      in the packet header.

3.  The Requirement  Requirements for Three and Applicability of 3-in-1 PCN Encoding States

3.1.  PCN Requirements

   The PCN architecture [RFC5559] describes proposed PCN schemes defines that
   expect traffic to be metered and marked using both Threshold and
   Excess Traffic schemes.  In order PCN-ingress-nodes of a
   PCN-domain control incoming packets.  Packets belonging to achieve this it is necessary PCN-
   controlled flows are subject to
   allow for three PCN encoding states: one as a Not Marked (NM) state metering and marking, they are
   termed PCN-packets, and PCN-ingress-nodes mark them as not-marked
   (PCN-colouring).  Any node in the other two to distinguish these PCN-domain may perform PCN metering
   and marking and mark PCN-packets if needed.  There are two levels of different
   metering and marking schemes: threshold-marking and excess-traffic-
   marking severity [RFC5670].  The way tunnels processed  Some edge behaviors require only a single marking
   scheme [I-D.ietf-pcn-sm-edge-behaviour], others require both
   [I-D.ietf-pcn-cl-edge-behaviour].  In the ECN field before
   [I-D.ietf-tsvwg-ecn-tunnel] severely limited how latter case, three PCN
   marking states are needed: not-marked (NM) to encode these
   states.

   The two bit ECN field seems indicate not-marked
   packets, threshold-marked (ThM) to offer four possible encoding states,
   but one (00) is set aside for traffic controlled indicate packets marked by transports that
   do not understand PCN marking [RFC5696], so it would be irregular the
   threshold-marker, and
   risky excess-traffic-marked (ETM) to use it as a PCN encoding state.  Of indicate packets
   marked by the three remaining ECN
   codepoints, only excess-traffic-marker [RFC5670].  As threshold-marking
   and excess-traffic-marking start marking packets at different load
   conditions, one (11) can be introduced by marking scheme indicates more severe pre-congestion
   than the other in terms of higher load.  If a congested node
   within packet has been marked
   by both a tunnel threshold-marker and still survive an excess-traffic-marker, it is marked
   with the decapsulation behaviour of more severe state.  Therefore, a
   tunnel egress fourth PCN marking state
   indicating that a packet is marked by both markers is not updated needed.

   Nonetheless, in addition to comply with [I-D.ietf-tsvwg-ecn-tunnel].
   The two remaining codepoints are (10) and (01).  But if a node within for the tunnel used either of these two remaining codepoints to try three PCN marking
   states a fourth codepoint is required to
   mark indicate packets with a second severity level, a tunnel that are
   not updated to
   comply with [I-D.ietf-tsvwg-ecn-tunnel] would remove this marking on
   decapsulation.  The ECN field was constrained to PCN-capable (termed the not-PCN codepoint).

   In all current PCN edge behaviors that use two marking states
   in this way irrespective of which earlier ECN tunnelling
   specification the tunnel complied with, whether regular IP in IP
   tunnelling [RFC3168] or IPsec tunnelling [RFC4301].

   One way to provide another encoding state that survives tunnelling schemes
   [RFC5559], [I-D.ietf-pcn-cl-edge-behaviour], excess-traffic-marking
   is
   to use a second Diffserv codepoint [I-D.ietf-pcn-3-state-encoding].
   Instead, to avoid wasting scarce Diffserv codepoints, a network
   operator can require tunnels in a PCN region to comply with
   [I-D.ietf-tsvwg-ecn-tunnel], thus removing the constraints imposed by
   earlier tunnelling specifications.

   Therefore this document presupposes tunnels in the PCN region comply configured with the newly proposed decapsulation rules defined in
   [I-D.ietf-tsvwg-ecn-tunnel].  Then the constraints of standard
   tunnels no longer apply so a larger reference rate than threshold-marking.
   We take this document can as a rule and define excess-traffic-marked as a 3-state
   encoding for PCN within one Diffserv codepoint.

4.  The 3-in-1 PCN more
   severe PCN-mark than threshold-marked.

3.2.  Requirements Imposed by Baseline Encoding

   The 3-in-1 PCN Encoding scheme is based closely on the baseline encoding defined in scheme [RFC5696] was defined so that there will it could
   be no compatibility
   issues if a PCN-domain evolves from using the baseline encoding
   scheme extended to accommodate an additional marking state.  It provides
   rules to embed the experimental scheme described here.  The exact manner
   in which the PCN encoding of two PCN states are carried in the IP header is
   shown in header.
   Figure 1.
         +--------+----------------------------------------------------+
         |        |           Codepoint in ECN field 1 shows the structure of IP header      |
         |  DSCP  |               <RFC3168 the former type-of-service field.  It
   contains the 6-bit Differentiated Services (DS) field that holds the
   DS codepoint name>             |
         |        +--------------+-------------+-------------+---------+
         |        | 00 <Not-ECT> | 10 <ECT(0)> | 01 <ECT(1)> | 11 <CE> |
         +--------+--------------+-------------+-------------+---------+
         | DSCP n |    Not-PCN   |      NM (DSCP) [RFC2474] and the 2-bit ECN field [RFC3168].
            0     1     2     3     4     5     6     7
         +-----+-----+-----+-----+-----+-----+-----+-----+
         |     ThM              DS FIELD             |   ETM ECN FIELD |
         +--------+--------------+-------------+-------------+---------+
         +-----+-----+-----+-----+-----+-----+-----+-----+

       Figure 1: 3-in-1 PCN Encoding

   In Figure 1 the 3 PCN states are encoded in Structure of the ECN former type-of-service field [RFC3168]
   of an in IP packet with its Diffserv field [RFC2474]

   Baseline encoding defines that the DSCP must be set to a PCN-
   compatible DSCP n,
   which is any PCN-Compatible DiffServ codepoint as defined in Section
   4.2 of n and the PCN baseline ECN-field [RFC3168] indicates the specific
   PCN-mark.  Baseline encoding [RFC5696]).  The PCN codepoint of a
   packet defines its marking state as follows:

   Not-PCN:  The packet is controlled by offers four possible encoding states
   within a transport that does not
      understand PCN marking, therefore single DSCP with the only valid action to notify
      congestion following restrictions.

   o  Codepoint `00' (not-ECT) is used to drop the packet;

   NM:  Not marked.  A packet in indicate non-PCN traffic as
      "not-PCN".  This allows the NM state has not (yet) had its
      marking state changed use of a DSCP for both PCN and non-PCN
      traffic.

   o  Codepoint `10' (ECT(0)) is used to indicate Not-marked PCN
      traffic.

   o  Codepoint `11' (CE) is used to indicate the ThM or ETM states, but it most severe PCN-mark.

   o  Codepoint `01' (ECT(1)) is available for experimental use and may
      be
      changed to one of these states by a node experiencing congestion
      or pre-congestion;

   ThM:  Threshold-marked.  Such a packet has had its marking state
      changed re-used by other PCN encodings such as the threshold-meter function [RFC5670];

   ETM:  Excess-traffic-marked.  Such presently defined
      3-in-1 PCN encoding.

3.3.  Applicability of 3-in-1 PCN Encoding

   When PCN traffic is tunneled IP-in-IP within a packet has had its marking state
      changed PCN-domain, PCN-marks
   must be preserved in all outer IP headers after encapsulation and
   decapsulation.  This property is violated by legacy encapsulation and
   decapsulation rules [RFC3168], [RFC4301] due to the excess-traffic-meter function [RFC5670].

   Packets marked NM, ThM or ETM are termed PCN-packets.  Their entry
   into way they treat
   the pcn-domain is controlled by edge nodes that understand how ECN field.  This led to process PCN markings [RFC5559].

5.  Behaviour strong limitations regarding how PCN-
   marks can be encoded using the ECN field of a PCN Node Compliant the IP header
   [I-D.ietf-pcn-encoding-comparison].  Therefore, baseline encoding
   [RFC5696] was defined which works well with legacy tunnels but
   supports only two PCN marking states.

   Since then, new rules have been defined for IP-in-IP tunneling
   [I-D.ietf-tsvwg-ecn-tunnel] so that the present 3-in-1 PCN Encoding

   To be compliant with encoding
   has more freedom to accommodate PCN-marks using the ECN field.  From
   this follows that 3-in-1 PCN Encoding, an PCN interior node
   behaves as follows:

   o  Except where explicitly stated otherwise, it MUST encoding may be applied only in PCN-
   domains that comply with [I-D.ietf-tsvwg-ecn-tunnel] or do not use
   tunneling.

4.  Definition of 3-in-1 PCN Encoding

   The 3-in-1 PCN encoding scheme is an extension of the baseline
   encoding specified scheme defined in [RFC5696] [RFC5696].  The PCN requirements and the
   extension rules for baseline encoding presented in the previous
   section determine how PCN encoding states are carried in the IP
   headers.  This is shown in Figure 2.
         +--------+----------------------------------------------------+
         |        |           Codepoint in ECN field of IP header      |
         |  DSCP  |               <RFC3168 codepoint name>             |
         |        +--------------+-------------+-------------+---------+
         |        | 00 <Not-ECT> | 10 <ECT(0)> | 01 <ECT(1)> | 11 <CE> |
         +--------+--------------+-------------+-------------+---------+
         | DSCP n |    Not-PCN   |      NM     |     ThM     |   ETM   |
         +--------+--------------+-------------+-------------+---------+

                       Figure 2: 3-in-1 PCN Encoding

   Like baseline encoding, 3-in-1 PCN encoding also uses a PCN
   compatible DSCP n and the ECN field for the encoding of PCN-marks.
   The PCN-marks have the following meaning.

   Not-PCN:  indicates a non-PCN-packet, i.e., a packet that is not
      subject to PCN metering and marking.

   NM:  Not-marked.  Indicates a PCN-packet that has not yet been marked
      by any PCN marker.

   ThM:  Threshold-marked.  Indicates a PCN-packet that has been marked
      by a threshold-marker [RFC5670].

   ETM:  Excess-traffic-marked.  Indicates a PCN-packet that has been
      marked by an excess-traffic-marker [RFC5670].

5.  Behaviour of a PCN Node Compliant with the 3-in-1 PCN Encoding

   To be compliant with the 3-in-1 PCN Encoding, an PCN interior node
   behaves as follows:

   o  It MUST change NM to ThM if the threshold-meter function indicates
      to mark the packet.

   o  It MUST change NM or ThM to ETM if the excess-traffic-meter
      function indicates to mark the packet.

   o  It MUST NOT change Not-PCN not-PCN to a PCN-Enabled codepoint NM, ThM, or ETM, and MUST NOT change
      a PCN-Enabled codepoint NM, ThM, or ETM to Not-PCN; not-PCN;

   o  It MUST NOT change ThM to NM;

   o  It MUST NOT change ETM to ThM or to NM;

   In other words, a PCN interior node MUST NOT mark PCN-packets into
   non-PCN packets and vice-versa, and it may increase the severity of
   packet marking
   the PCN-mark of a PCN-packet, but it MUST NOT decrease it, where it.

6.  Backward Compatibility

   Discussion of backward compatibility between PCN encoding schemes and
   previous uses of the ECN field is given in Section 6 of [RFC5696].

6.1.  Backward Compatibility with Pre-existing PCN Implementations

   This encoding complies with the rules for extending the baseline PCN
   encoding schemes in Section 5 of [RFC5696].

   The term "compatibility" is meant in the following sense.  It is
   possible to operate nodes with baseline encoding [RFC5696] and 3-in-1
   encoding in the same PCN domain.  The nodes with baseline encoding
   MUST perform excess-traffic-marking because the 11 codepoint of
   3-in-1 encoding also means excess-traffic-marked.  PCN-boundary-nodes
   of such domains are required to interpret the full 3-in-1 encoding
   and not just baseline encoding, otherwise they cannot interpret the
   01 codepoint.

   Using nodes that perform only excess-traffic-marking may make sense
   in networks using the CL edge behavior
   [I-D.ietf-pcn-cl-edge-behaviour].  Such nodes are able to notify the
   egress only about severe pre-congestion when traffic needs to be
   terminated.  This seems reasonable for locations that are not
   expected to see any pre-congestion, but excess-traffic-marking gives
   them a means to terminate traffic if unexpected overload still
   occurs.

6.2.  Recommendations for the Use of PCN Encoding Schemes

   This sub-section is informative not normative.
         +------------------------+------------------------------------+
         |  Used marking schemes  |  Recommended PCN encoding scheme   |
         +------------------------+------------------------------------+
         | Only threshold-marking |     Baseline encoding [RFC5696]    |
         +------------------------+------------------------------------+
         | Only excess-traffic-   |     Baseline encoding [RFC5696]    |
         |       marking          |  or 3-in-1 PCN encoding            |
         +------------------------+------------------------------------+
         | Threshold-marking and  |     3-in-1 PCN encoding            |
         | excess-traffic-marking |                                    |
         +------------------------+------------------------------------+

                   Figure 3: Use of PCN encoding schemes

   Figure 3 gives guidelines under which conditions baseline encoding
   and 3-in-1 PCN encoding would typically be used.

6.2.1.  Use of Both Excess-Traffic-Marking and Threshold-Marking

   If both excess-traffic-marking and threshold-marking are enabled in a
   PCN-domain, 3-in-1 encoding should be used as described in this
   document.

6.2.2.  Unique Use of Excess-Traffic-Marking

   If only excess-traffic-marking is enabled in a PCN-domain, baseline
   encoding or 3-in-1 encoding may be used.  They lead to the same
   encoding because PCN-boundary nodes will interpret baseline "PCN-
   marked (PM)" as "excess-traffic-marked (ETM)".

6.2.3.  Unique Use of Threshold-Marking

   No scheme is currently proposed to solely use threshold-marking.
   However, if only threshold-marking is enabled in a PCN-domain,
   baseline encoding SHOULD be used.  This is because threshold marking
   will work in combination with legacy tunnel decapsulators within the
   PCN-domain, while using threshold marking with the 3-in-1 encoding
   requires that tunnel decapsulators within a PCN-domain comply with
   [I-D.ietf-tsvwg-ecn-tunnel].

7.  IANA Considerations

   This memo includes no request to IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

8.  Security Considerations

   The security concerns relating to this extended PCN encoding are the
   same as those in [RFC5696].  In summary, PCN-boundary nodes are
   responsible for ensuring inappropriate PCN markings do not leak into
   or out of a PCN domain, and the current phase of the PCN architecture
   assumes that all the nodes of a PCN-domain are entirely under the
   control of a single operator, or a set of operators who trust each
   other.

   Given the only difference between the baseline encoding and the
   present 3-in-1 encoding is the order use of
   severity increases from NM through ThM to ETM.

6.  IANA Considerations

   This memo includes the 01 codepoint, no request to IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

7.  Security Considerations

   The new
   security concerns relating to this extended PCN encoding issues are the
   same raised, as those this codepoint was already available
   for experimental use in [RFC5696].

8. the baseline encoding.

9.  Conclusions

   The 3-in-1 PCN Encoding provides three states to encode PCN markings
   in encoding uses a PCN-compatible DSCP and the ECN field of an IP packet using just one Diffserv codepoint.
   to encode PCN-marks.  One state is for not marked packets while codepoint allows non-PCN traffic to be
   carried with the two others are for same PCN-compatible DSCP and three other codepoints
   support three PCN
   nodes to mark packets marking states with increasing different levels of severity.  Use
   The use of this PCN encoding scheme presupposes that any tunnels in
   the PCN region have been updated to comply with
   [I-D.ietf-tsvwg-ecn-tunnel].

9.

10.  Acknowledgements

   Thanks to Phil Eardley, Teco Boot, and Kwok Ho Chan and Michael Menth for reviewing this.

10.
   this document.

11.  Comments Solicited

   To be removed by RFC Editor: Comments and questions are encouraged
   and very welcome.  They can be addressed to the IETF Congestion and
   Pre-Congestion working group mailing list <pcn@ietf.org>, and/or to
   the authors.

11.

12.  References

11.1.
12.1.  Normative References

   [I-D.ietf-tsvwg-ecn-tunnel]
              Briscoe, B., "Tunnelling of Explicit Congestion
              Notification", draft-ietf-tsvwg-ecn-tunnel-08 (work in
              progress), March 2010.

   [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.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, September 2001.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC5129]  Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion
              Marking in MPLS", RFC 5129, January 2008.

   [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.

11.2.

12.2.  Informative References

   [I-D.ietf-pcn-3-state-encoding]
              Briscoe, B.,

   [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-06 (work in progress),
              June 2010.

   [I-D.ietf-pcn-encoding-comparison]
              Chan, K., Karagiannis, G., Moncaster, T., and M. Menth, "A PCN encoding
              using 2 DSCPs to provide 3 or more states",
              draft-ietf-pcn-3-state-encoding-01 M.,
              Eardley, P., and B. Briscoe, "Pre-Congestion Notification
              Encoding Comparison",
              draft-ietf-pcn-encoding-comparison-02 (work in progress),
              February
              March 2010.

   [RFC4301]  Kent, S.

   [I-D.ietf-pcn-sm-edge-behaviour]
              Charny, A., Karagiannis, G., Menth, M., and K. Seo, "Security Architecture T. Taylor,
              "PCN Boundary Node Behaviour for the
              Internet Protocol", RFC 4301, December 2005. Single Marking (SM)
              Mode of Operation", draft-ietf-pcn-sm-edge-behaviour-03
              (work in progress), June 2010.

   [I-D.ietf-tsvwg-ecn-tunnel]
              Briscoe, B., "Tunnelling of Explicit Congestion
              Notification", draft-ietf-tsvwg-ecn-tunnel-08 (work in
              progress), March 2010.

Authors' Addresses

   Bob Briscoe
   BT
   B54/77, Adastral Park
   Martlesham Heath
   Ipswich  IP5 3RE
   UK

   Phone: +44 1473 645196
   Email: bob.briscoe@bt.com
   URI:   http://bobbriscoe.net/

   Toby Moncaster
   BT
   c/o B54/70, Adastral Park
   Martlesham Heath
   Ipswich  IP5 3RE
   UK
   Independent

   Email: toby@moncaster.com

   Michael Menth
   University of Wuerzburg
   room B206, Institute of Computer Science
   Am Hubland
   Wuerzburg  97074
   Germany

   Phone: +44 1206 332805 +49 931 31 86644
   Email: toby.moncaster@bt.com menth@informatik.uni-wuerzburg.de