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Versions: 00 01 02 03 04 draft-ietf-tsvwg-tunnel-congestion-feedback

Internet Engineering Task Force                                   X. Wei
INTERNET-DRAFT                                                     L.Zhu
Intended Status: Standards Track                     Huawei Technologies
Expires: January 2, 2016                                          L.Deng
                                                            China Mobile
                                                               B.Briscoe
                                                            July 1, 2015


                       Tunnel Congestion Feedback
             draft-wei-tsvwg-tunnel-congestion-feedback-04


Abstract

   This document describes a mechanism to calculate congestion of a
   tunnel segment based on RFC 6040 recommendations, and a feedback
   protocol by which to send the measured congestion of the tunnel from
   egress to ingress . A basic  model for measuring tunnel congestion
   and feedback is described, and a protocol for carrying the feedback
   data is outlined.


Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html


Copyright and License Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the



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   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.



Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3. Congestion Information Feedback Models  . . . . . . . . . . . .  4
     3.1 Direct Model . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2 Centralized Model  . . . . . . . . . . . . . . . . . . . . .  4
   4. Congestion Level Measurement  . . . . . . . . . . . . . . . . .  5
   5. Congestion Information Delivery . . . . . . . . . . . . . . . .  7
     5.1 IPFIX Extentions . . . . . . . . . . . . . . . . . . . . . .  7
       5.1.1 ce-cePacketTotalCount  . . . . . . . . . . . . . . . . .  7
       5.1.2 ect-nectPacketTotalCount . . . . . . . . . . . . . . . .  8
       5.1.3 ce-nectPacketTotalCount  . . . . . . . . . . . . . . . .  8
       5.1.4 ce-ectPacketTotalCount . . . . . . . . . . . . . . . . .  8
       5.1.5 ect-ectPacketTotalCount  . . . . . . . . . . . . . . . .  9
   6. Congestion Management . . . . . . . . . . . . . . . . . . . . .  9
   7. Security  . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10
   9. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.1  Normative References  . . . . . . . . . . . . . . . . . . . 10
     9.2  Informative References  . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11















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1. Introduction

   In IP network, persistent congestion (or named congestion collapse)
   would cause transport throughput to drop down, lead to waste of
   network resource, so appropriate congestion control mechanisms are
   critical to make sure the network not fall into persistent congestion
   state. Currently, transport protocols such as TCP, SCTP, DCCP, has
   their built-in congestion control mechanism, and even for certain
   single transport protocol like TCP there could be a couple of
   different congestion control mechanism to choose. All these
   congestion control mechanisms are implemented on host side, and there
   are reasons that only host side congestion control is not sufficient
   for the whole network to keep away from persistent congestion, e.g.,
   (1) some protocol's congestion control scheme might has internal
   design flaws; (2) improper software implementation of protocol; (3)
   some transport protocols even don't provide congestion control at
   all.

   In order to have a better control on network congestion status, it's
   necessary for the network side to do certain kind of traffic control.
   For example, ConEx [ConEx] provides a method for network operator to
   learn about traffic's congestion contribution information, and then
   congestion management action could be taken based on this
   information.

   Tunnels are widely deployed in various networks including public
   Internet, datacenter network, and enterprise network etc, a tunnel
   consists of an ingress, an egress and a set of interior routers. For
   the tunnel scenario, a tunnel-based mechanism which is different from
   ConEx is introduced for network traffic control to keep network away
   from persistent congestion; in this case, tunnel ingress will
   implement congestion management function to control the traffic
   entering the tunnel.

   In order to do congestion management at ingress, the ingress must
   first get the inner tunnel congestion level information. But the
   ingress cannot use the locally visible traffic rates, because it
   would require additional knowledge of downstream capacity and
   topology, as well as cross traffic that does not pass through this
   ingress.

   This document provide a mechanism of feeding back inner tunnel
   congestion level to ingress, using this mechanism the egress could
   feed the tunnel congestion level information it collects back to
   ingress, after receiving the information ingress could do congestion
   management according to network management policy.

2. Conventions



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   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]

3. Congestion Information Feedback Models

   According to specific network deployment, there are two kinds of
   feedback model: direct model and centralized model.

3.1 Direct Model
                           Feedback
          |-----------------------------------------|
          |                                         |
          |                                         |
          |                                         V
      +----------+         tunnel            +-----------+
      |Egress    |========================== |Inress     |
      |(Exporter)|                           |(Collector)|
      +----------+                           +-----------+

      (a) Direct Feedback Model.

   Direct model means egress feeds information directly to ingress. In
   this model, egress collects network congestion level information and
   feedback the information to ingress for congestion management. The
   ingress here will act as both decision point that decides how to do
   congestion management and action point that implements congestion
   management decision.

3.2 Centralized Model


    Feedback    +-----------+
      --------->|Controller |#####################
      |         |(Collector)|                    #
      |         +-----------+                    #
      |                                          #
   +----------+          tunnel            +-----V-+
   |Egress    | ===========================|Ingress|
   |(Exporter)|                            +-------+
   +----------+

   (b) Centralized Feedback Model


   There are scenarios that ingress only takes the role of action point,
   and it implements traffic control decision from another entity, named
   "controller" here.



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   In this model, after egress collects network congestion level
   information, it feeds back the information to controller instead of
   ingress, and then the controller makes congestion management decision
   and sends the decision to ingress.

4. Congestion Level Measurement

   This section describes how to measure congestion level in tunnel.

   There may be different approaches of packet loss detection for
   different tunneling protocol scenarios, for instance, if there is a
   sequence field in tunneling protocol header, it will be easy for
   egress to detect packet loss through the gaps in sequence number
   space; another approach is to compare the number of packets entering
   ingress and the number of packets arriving at egress over the same
   span of packets. This document will focus on the latter one which is
   a more general approach.

   If the routers support ECN, after router's queue length is over a
   predefined threshold, the routers will marks ECN packets as CE
   packets or drop not-ECN packets with the probability proportional to
   queue length, if the queue overflows all packets will be dropped; if
   the routers don't support ECN, after router's queue length is over a
   predefined threshold, the routers will drop both ECN packets and not-
   ECN packets with the probability proportional to queue length. It's
   assumed all routers in the tunnel support ECN.

   Faked ECT is used at ingress to defer packet loss to egress. The
   basic idea of faked ECT is that, when encapsulating packets, ingress
   first marks tunnel outer header according to RFC6040, and then
   remarks outer header of Not-ECT packet as ECT, there will be three
   kinds of combination of outer header ECN field and inner header ECN
   field: CE|CE, ECT|N-ECT, ECT|ECT (in the form of outer ECN| inner
   ECN).

   In case all interior routers support ECN, the network congestion
   level could be indicated through the ratio of CE-marked packet and
   the ratio of packet drop, the relationship between these two kinds of
   indicator is complementary. If the congestion level in tunnel is not
   high enough, the packets would be marked as CE instead of being
   dropped, and then it is easy to calculate congestion level according
   to the ratio of CE-marked packets; if the congestion level is so high
   that ECT packet will be dropped, then the packet loss ratio could be
   calculated by comparing total packets entering ingress and total
   packets arriving at egress over the same span of packets, if packet
   loss is detected, it could be assumed that severe congestion has
   occurred in the tunnel, because loss is only ever a sign of serious
   congestion, so it doesn't need to measure loss ratio accurately.



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   The basic procedure of congestion level measurement is as follows:


           +-------+                 +------+
           |Ingress|                 |Egress|
           +-------+                 +------+
               |                         |
       +----------------+                |
       |cumulative count|                |
       +----------------+                |
               |                         |
               | <node id-i, ECN counts> |
               |------------------------>|
               |<node id-e, ECN counts>  |
               |<------------------------|
               |                         |
               |                         |


   (a) Direct model feedback procedure

        +----------+    +-------+                 +------+
        |Controller|    |Ingress|                 |Egress|
        +----------+    +-------+                 +------+
             |              |                         |
             |      +----------------+                |
             |      |cumulative count|                |
             |      +----------------+                |
             |              |                         |
             |              | <node id-i, ECN counts> |
             |              |------------------------>|
             |              |                         |
             |                                        |
             |                                        |
             |       <node id-i, ECN counts>          |
             |       <node id-e, ECN counts>          |
             |<---------------------------------------|
             |                                        |
             |                                        |
             |                                        |

   (b) Centralized model feedback procedure

   Ingress encapsulates packets and marks outer header according to
   faked ECT as described above. Ingress cumulatively counts packets for
   three types of ECN combination (CE|CE, ECT|N-ECT, ECT|ECT) and then
   the ingress regularly sends cumulative packet counts message of each
   type of ECN combination to the egress. When each message arrives, the



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   egress cumulatively counts packets coming from the ingress and adds
   its own packet counts of each type of ECN combination (CE|CE, ECT|N-
   ECT, CE|N-ECT, CE|ECT, ECT|ECT) to the message and either returns the
   whole message to the ingress, or to a central controller.

   The counting of packets could be at the granularity of the all
   traffic from the ingress to the egress to learn about the overall
   congestion status of the path between the ingress and the egress; or
   at the granularity of individual customer's traffic or a specific set
   of flows to learn about their congestion contribution.

5. Congestion Information Delivery

   As described above, the tunnel ingress needs to convey message of
   cumulative packet counts of each type of ECN combination to tunnel
   egress, and the tunnel egress also needs to feed the message of
   cumulative packet counts of each type of ECN combination to the
   ingress or central collector. This section describes how the messages
   could be conveyed.

   The message could be along the same path with network data traffic,
   referred as in band signal; or go through a different path with
   network data traffic, referred as out of band signal. Because out of
   band scheme needs additional separate path which might limit its
   actual deployment, so the in band scheme will be discussed here.

   Because the message is transmitted in band, so the message packet
   might get lost in case of network congestion. To cope with the
   situation that message packet gets lost, the packet counts values are
   sent as cumulative counters, so if a message is lost the next message
   will recover the missing information.

   IPFIX [RFC7011] is selected as a choice of candidate protocol. IPFIX
   is preferred to use SCTP as transport, and because SCTP allows
   partially reliable delivery [RFC3758], which makes sure the feedback
   message will not be blocked to be sent in case of SCTP packets lost
   due to network congestion.

   When sending message from ingress to egress, the ingress acts as
   IPFIX exporter and egress acts as IPFIX collector; when sending
   message from egress to ingress or controller, the egress acts as
   IPFIX exporter and ingress or controller acts as IPFIX collector.

5.1 IPFIX Extentions

5.1.1 ce-cePacketTotalCount

   Description: The total number of incoming packets with CE|CE ECN



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   marking combination for this Flow at the Observation Point since the
   Metering Process (re-)initialization for this Observation Point.

   Abstract Data Type: unsigned64

   Data Type Semantics: totalCounter

   ElementId: TBD1

   Statues: current

   Units: packets

5.1.2 ect-nectPacketTotalCount

   Description: The total number of incoming packets with ECT|N-ECT ECN
   marking combination for this Flow at the Observation Point since the
   Metering Process (re-)initialization for this Observation Point.

   Abstract Data Type: unsigned64

   Data Type Semantics: totalCounter

   ElementId: TBD2

   Statues: current

   Units: packets

5.1.3 ce-nectPacketTotalCount

   Description: The total number of incoming packets with CE|N-ECT ECN
   marking combination for this Flow at the Observation Point since the
   Metering Process (re-)initialization for this Observation Point.

   Abstract Data Type: unsigned64

   Data Type Semantics: totalCounter

   ElementId: TBD3

   Statues: current

   Units: packets

5.1.4 ce-ectPacketTotalCount

   Description: The total number of incoming packets with CE|ECT ECN



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   marking combination for this Flow at the Observation Point since the
   Metering Process (re-)initialization for this Observation Point.

   Abstract Data Type: unsigned64

   Data Type Semantics: totalCounter

   ElementId: TBD4

   Statues: current

   Units: packets

5.1.5 ect-ectPacketTotalCount

   Description: The total number of incoming packets with ECT|ECT ECN
   marking combination for this Flow at the Observation Point since the
   Metering Process (re-)initialization for this Observation Point.

   Abstract Data Type: unsigned64

   Data Type Semantics: totalCounter

   ElementId: TBD5

   Statues: current

   Units: packets

6. Congestion Management

   After tunnel ingress (or controller) receives congestion level
   information, then congestion management actions could be taken based
   on the information, e.g. if the congestion level is higher than a
   predefined threshold, then action could be taken to reduce the
   congestion level.

   Congestion management action must be delayed by more than a worst-
   case global RTT, otherwise tunnel traffic management will not give
   normal e2e congestion control enough time to do its job, and the
   system could go unstable. The detailed description of congestion
   management is out of scope of this document, as examples, congestion
   management such as circuit breaker [CB] and congestion policing [CP]
   could be applied.

7. Security

   This document describes the tunnel congestion calculation and



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   feedback. For feeding back congestion, security mechanisms of IPFIX
   are expected to be sufficient. No additional security concerns are
   expected.

8. IANA Considerations

   This document defines a set of new IPFIX Information Elements (IE).
   New registry for these IE identifiers is needed.

   TBD1~TBD5.

9. References

9.1  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, September 2001, <http://www.rfc-
              editor.org/info/rfc3168>.

   [RFC3758]  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
              Conrad, "Stream Control Transmission Protocol (SCTP)
              Partial Reliability Extension", RFC 3758, May 2004,
              <http://www.rfc-editor.org/info/rfc3758>.

   [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
              "Specification of the IP Flow Information Export (IPFIX)
              Protocol for the Exchange of Flow Information", STD 77,
              RFC 7011, September 2013, <http://www.rfc-
              editor.org/info/rfc7011>.



9.2  Informative References

   [CONEX] Matt Mathis, Bob Briscoe. "Congestion Exposure (ConEx)
              Concepts, Abstract Mechanism and Requirements", draft-
              ietf-conex-abstract-mech-13, October 24, 2014

   [CB] G. Fairhurst. "Network Transport Circuit Breakers", draft-ietf-
              tsvwg-circuit-breaker-01, April 02, 2015

   [CP] Bob Briscoe,  Murari Sridharan. "Network Performance Isolation
              in Data Centres using Congestion Policing", draft-briscoe-



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              conex-data-centre-02,  February 14, 2014

Authors' Addresses

   Xinpeng Wei
   Beiqing Rd. Z-park No.156, Haidian District,
   Beijing,  100095, P. R. China
   E-mail: weixinpeng@huawei.com



   Zhu Lei
   Beiqing Rd. Z-park No.156, Haidian District,
   Beijing,  100095, P. R. China
   E-mail:lei.zhu@huawei.com



   Lingli Deng
   Beijing,  100095, P. R. China
   E-mail: denglingli@gmail.com



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






















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