ConEx                                                         B. Briscoe
Internet-Draft                                                        BT
Intended status: Informational                         November 24, 2011
Expires: May 27, 2012


        Initial Congestion Exposure (ConEx) Deployment Examples
                 draft-briscoe-conex-initial-deploy-01

Abstract

   This document gives examples of how ConEx deployment might get
   started, focusing on unilateral deployment by a single network.

Status of This Memo

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   This Internet-Draft will expire on May 27, 2012.

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   Copyright (c) 2011 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Recap: Incremental Deployment Features of the ConEx
       Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  ConEx Components . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Recap of Basic ConEx Components  . . . . . . . . . . . . .  4
     3.2.  Per-Network Deployment Concepts  . . . . . . . . . . . . .  4
   4.  Example Initial Deployment Arrangements  . . . . . . . . . . .  5
     4.1.  Single Receiving Network Scenario  . . . . . . . . . . . .  5
       4.1.1.  ConEx Functions in the Single Receiving Network
               Scenario . . . . . . . . . . . . . . . . . . . . . . .  7
       4.1.2.  Incentives to Unilaterally Deploy ConEx in a
               Receiving Network  . . . . . . . . . . . . . . . . . .  8
     4.2.  Mobile Network Scenario  . . . . . . . . . . . . . . . . .  9
     4.3.  Scenario Internal to a Multi-Tenant Data Centre  . . . . .  9
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . .  9
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  Informative References . . . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Summary of Changes between Drafts . . . . . . . . . . 10





























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1.  Introduction

   This document gives examples of how ConEx deployment might get
   started, focusing on unilateral deployment by a single network.

2.  Recap: Incremental Deployment Features of the ConEx Protocol

   The ConEx mechanism document [ConEx-Abstract-Mech] goes to great
   lengths to design for incremental deployment in all the respects
   below.  It should be referred to for precise details on each of these
   points:

   o  The ConEx mechanism is essentially a change to the source, in
      order to re-insert congestion feedback into the network.

   o  Source-host-only deployment is possible without any negotiation
      required, and individual transport protocol implementations within
      a source host can be updated separately.

   o  Receiver modification may optionally improve ConEx for some
      transport protocols with feedback limitations (TCP being the main
      example), but it is not a necessity

   o  Proxies for the source and/or receiver are feasible (though not
      necessarily straightforward)

   o  Queues and network forwarding do not require any modification for
      ConEx.

   o  ECN is not required in the network for ConEx.  If some network
      nodes support ECN, it can be used by ConEx.

   o  ECN is not required at the receiver for ConEx.  The sender should
      nonetheless attempt to negotiate ECN-usage with the receiver,
      given some aspects of ConEx work better the more ECN is deployed,
      particularly auditing and border measurement.

   o  Given ConEx exposes information for IP-layer policy devices to
      use, the design does not preclude possible innovative uses of
      ConEx information by other IP-layer devices, e.g. forwarding
      itself

   o  Packets indicate whether or not they support ConEx.








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3.  ConEx Components

3.1.  Recap of Basic ConEx Components

   [ConEx-Abstract-Mech] introduces the following components:

   o  The ConEx Wire Protocol

   o  Forwarding devices (unmodified)

   o  Sender (modified for ConEx)

   o  Receiver (optionally modified)

   o  Audit

   o  Policy Devices:

      *  Rest-of-Path Congestion Monitoring Devices

      *  Congestion Policers

   [ConEx-Abstract-Mech] should be referred to for definitions of each
   of these components and further explanation.

3.2.  Per-Network Deployment Concepts

   Network deployment-related definitions:

   Internet Ingress:  The first IP node a packet traverses that is
      outside the source's own network.  In a domestic network that will
      be the first node downstream from the home access equipment.  In
      an enterprise network this is the provider edge router.

   Internet Egress:  The last IP node a packet traverses before reaching
      the receiver's network.

   ConEx-Enabled Network:  A network whose edge nodes implement ConEx
      policy functions.

   Each network can unilaterally choose to use any ConEx information
   given by those sources using ConEx, independently of whether other
   networks use it.

   Typically, a network will use ConEx information by deploying a policy
   function at the ingress edge of its network to monitor arriving
   traffic and to act in some way on the congestion information in those
   packets that are ConEx-enabled.  Actions might include policing,



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   altering the class of service, or re-routing.  Alternatively, less
   direct actions via a management system might include triggering
   capacity upgrades, triggering penalty clauses in contracts or levying
   charges between networks based on ConEx measurements.

   Typically, a network using ConEx info will deploy a ConEx policy
   function near the ingress edge and a ConEx audit function near the
   egress edge.  The segment of the path between a ConEx policy function
   and a ConEx audit function can be considered to be a ConEx-protected
   segment of the path.  Assuming a network covers all its ingresses and
   egresses with policy functions and audit functions respectively, the
   network within this ring will be a ConEx-protected network.

   Of course, because each edge device usually serves as both an ingress
   and an egress, the two functions are both likely to be present in
   each edge device.

4.  Example Initial Deployment Arrangements

   In all the deployment scenarios below, we assume that deployment
   starts with some data sources being modified with ConEx code.  The
   rationale for this is that the developer of a scavenger transport
   protocol like LEDBAT has a strong incentive to tell the network how
   little congestion it is causing despite sending large volumes of
   data.  In this case the developer makes the first move expecting it
   will prompt at least some networks to move in response--so that they
   use the ConEx information to reward users of the scavenger protocol.

4.1.  Single Receiving Network Scenario

   The name 'Receiving Network' for this scenario merely emphasises that
   most data is arriving from connected networks and data centres and
   being consumed by residential customers on this access network.  Some
   data is of course also travelling in the other direction.

















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                                          DSLAMs __
                                              /|/     ,-.Home-a
                                        __/__| |-----(   )
                    ,-----.            /  \  | |---   `-'
       ,---.       /       \  ,------P/       \|\__
      /     \     '  Core   '/| BRAS |          __
     ( Peer  )-->-|P        | '------'       /|/
      \     /     |         |          _____| |---
       '---`      '         '\,------./     | |---
                   \ M     /  |BRAS  |       \|\__
                    `-----'   '------A\          __
                     |          P|     \      /|/
                    /|\         /|\     \__\_| |---   ,-.
                   ,---.        ,---.      / | |-----(   )
                  /Data \      /     \        \|\__   `-'Home-b
                 ( Centre)    (  CDN  )
                  \     /      \     /  Access Network
                   '---`        '---`  <------------->


   P=Congestion-Policer; M=Congestion-Monitor; A=Audit function

                Figure 1: Single Receiving Network Scenario

   Figure Figure 1 is an attempt to show the salient features of a ConEx
   deployment in a typical broadband access provider's network (within
   the constraints of ASCII art).  Broadband remote access servers
   (BRASs) control access to the core network from the access network
   and vice versa.  Home networks (and small businesses) connect to the
   access network, but only two are shown.

   In this diagram, all data is travelling towards the access network of
   Home-b, from the Peer network, the Data centre, the CDN and Home-a.
   Data actually travels in both directions on all links, but only one
   direction is shown.

   The data centre, core and access network are all run by the same
   network operator, but each is the responsibility of a different
   department with internal accounting between them.  The content
   distribution network (CDN) is operated by a third party CDN provider,
   and of course the peer network is also operated by a third party.

   This operator of the data centre, core and access network is the only
   one in the diagram to have deployed ConEx monitoring and policy
   devices at the edges of its network.  However, it has not enabled ECN
   on any of its network elements and neither has any other network in
   the diagram.  The operator has deployed a congestion policing
   function (P) on the provider-edge router where the peer attaches to



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   its core, on the BRAS where the CDN attaches and on the other BRAS
   where each of the residential customers like Home-a attach.  On the
   provider-edge router where the data centre attaches it has deployed a
   congestion monitoring function (M).  Each of these policing and
   monitoring functions handles the aggregate of all traffic traversing
   it, for all destinations.

   The operator has deployed an audit function on each logical output
   port of the BRAS for each end-customer site like Home-b.  The Audit
   function handles the aggregate of all traffic for that end-customer
   from all sources.  For traffic in the opposite direction (e.g. from
   Home-b to Home-a, there would be equivalent policing (P) and audit
   (A) functions in the converse locations to those shown.

   Some content sources in the CDN and in the data centre are using the
   ConEx protocol, but others are not.  There is a similar situation for
   hosts attached to the Peer network and hosts in home networks like
   Home-a: some are sending ConEx packets at least for bulk data
   transports, while others are not.

4.1.1.  ConEx Functions in the Single Receiving Network Scenario

   Within the BRAS there are logical ports that model the rate of each
   access line from the DSLAM to each home network [TR-059].  They are
   fed by a shared queue that models the rate of the downstream link
   from the BRAS to the DSLAM (sometimes called the backhaul network).
   If there is congestion anywhere in the set of networks in Figure
   Figure 1 it is nearly always:

   o  either self-congestion in the queues into the logical ports
      representing the access lines

   o  or shared congestion in the shared queue on the BRAS that feeds
      them.

   Any ConEx sources sending data through this BRAS will receive
   feedback about these losses from the destination and re-insert it as
   ConEx markings into the data.  Figure 2 shows an example plot of the
   loss levels that might be seen at different monitoring points along a
   path between the data centre and home-b, for instance.  The top half
   of the figure shows the loss probability within the BRAS consists of
   0.1% at the shared queue and 0.2% self-congestion in the logical
   output port that models the access line, making 0.3% in total.  This
   upper diagram also shows whole path congestion as signalled by the
   ConEx sender, which remains unchanged along the whole path at 0.3%.

   The lower half of the figure shows (downstream congestion) = (whole
   path) - (upstream congestion).  Upstream congestion can only be



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   monitored locally where the loss actually happens (within the BRAS
   output queues).  Nonetheless, given there is rarely loss anywhere
   else but within the BRAS, this limitation is not significant in this
   scenario.  The lower half of the figure also shows the location of
   the policing and audit functions.  Policing anywhere within or
   upstream ofthe BRAS will be based on the downstream congestion level
   of 0.3%.  While Auditing within the BRAS but after all the queues can
   check that the whole path congestion signalled by ConEx is no less
   than the loss levels experienced within the BRAS itself.

      Data centre-->|<--core-->|<------BRAS--------->|<--Home--
                               |                     |
    ^loss                      |<-Shared->|<-Access->|
    |probability                 backhaul
    |
0.3%|- - - - - - - - - - - - - - - - - - - - +-----------------
    |      whole path congestion             |
    |                                        |
    |                                        |upstream
0.1%|                              +---------+congestion
    |                              |
   -O==============================+----------------------------->
                                                        monitoring point
    ^loss
    |probability   Policing                    Audit
    |                |                            |
    |                V                            |
0.3%|----------------O-------------+              |
    |                              |downstream    |
0.2%|                              +---------+    |
    |                              congestion|    |
    |                                        |    |
    |                                        |    V
   -O----------------------------------------+====O============-->
                                                        monitoring point

            Figure 2: Example plot of loss levels along a path

4.1.2.  Incentives to Unilaterally Deploy ConEx in a Receiving Network

   Even a sending application that is modified to use ConEx can choose
   whether to send ConEx or Not-ConEx packets.  Nonethelss, ConEx
   packets bring information to a policer about congestion expected on
   the rest of the path beyond the policer.  Not-ConEx packets bring no
   such information.  Therefore a network that has deployed ConEx
   policers will tend to rate-limit not-ConEx packets conservatively in
   order to manage the unknown risk of congestion.  In contrast, a
   network doesn't normally need to rate-limit ConEx-enabled packets



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   unless they reveal a persistently high contribution to congestion.
   This natural tendency for networks to favour senders that provide
   ConEx information encourages senders to choose to use the ConEx
   protocol whenever they can.

   {ToDo: complete this section}

4.2.  Mobile Network Scenario

   Placeholder for summary of the scenario in a mobile network described
   in [conex-mobile]

   In mobile networks, both mobile terminals and mobile network
   equipment are standardised by the 3GPP.  If the 3GPP were to adopt
   the ConEx protocol, it might mandate ConEx implementation for
   compliant equipment.

   {ToDo: Describe how a central traffic management box can arrange to
   remotely view upstream congestion as it would be seen from the
   interface with the mobile terminal.}

4.3.  Scenario Internal to a Multi-Tenant Data Centre

   A number of companies offer hosting of virtual machines on their data
   centre infrastructure--so-called infrastructure as a service (IaaS).
   A set amount of processing power, memory, storage and network are
   offered.  Although processing power, memory and storage are
   relatively simple to allocate on the 'pay as you go' basis that has
   become common, the network is less easy to allocate given it is a
   naturally distributed system.

   {ToDo: Complete this section.}

5.  Security Considerations

6.  IANA Considerations

   This document does not require actions by IANA.

7.  Conclusions

   {ToDo}

8.  Acknowledgments







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9.  Informative References

   [ConEx-Abstract-Mech]  Mathis, M. and B. Briscoe, "Congestion
                          Exposure (ConEx) Concepts and Abstract
                          Mechanism", draft-ietf-conex-abstract-mech-03
                          (work in progress), October 2011.

   [Seawall]              Shieh, A., Kandula, S., Greenberg, A., and C.
                          Kim, "Seawall: Performance Isolation in Cloud
                          Datacenter Networks", Proc 2nd USENIX Workshop
                          on Hot Topics in Cloud Computing , June 2010,
                          <http://research.microsoft.com/en-us/projects/
                          seawall/>.

   [TR-059]               Anschutz, T., Ed., "DSL Forum Technical Report
                          TR-059: Requirements for the Support of QoS-
                          Enabled IP Services", September 2003.

   [conex-mobile]         Kutscher, D., Mir, F., Winter, R., Krishnan,
                          S., and Y. Zhang, "Mobile Communication
                          Congestion Exposure Scenario",
                          draft-kutscher-conex-mobile-00 (work in
                          progress), March 2011.

Appendix A.  Summary of Changes between Drafts

   Detailed changes are available from
   http://tools.ietf.org/id/draft-briscoe-conex-initial-deploy-00.txt

   From draft-briscoe-00 to draft-briscoe-01:  Re-issued without textual
      change.  Merely re-submitted to correct a processing error causing
      the whole text of draft-00 to be duplicated within the file.

Author's Address

   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/






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