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Cross-Layer Interaction in Overlay Networks

VIEWS: 18 PAGES: 41

  • pg 1
									Cross-Layer Interaction in
    Overlay Networks


   Srinivasan Seetharaman
Georgia Institute of Technology
     srini@cc.gatech.edu


         August 2007
Data Communication




       Application Layer
    (HTTP, FTP, BitTorrent)
       Transport Layer
         (TCP, UDP)
                                  Combined functioning
        Network Layer           determines end-to-end
        (IP protocols)        network characteristics
          Link Layer
          (Ethernet)
                               (like delay, throughput)
        Physical Layer
        (Fiber Optical)
                                                          2
Internet Architecture

 Current Internet architecture has been guided by
 the end-to-end principle:
    network layer implements simple primitives
    useful for a broad range of end-to-end applications
    for good balance between cost vs benefit




                                                           3
Internet Evolution
 A survey of Cisco router software features…

                Feature                  Year    Version
   Fault restoration                     1986    SSR 1
   Multicast                             1994   IOS 10.2
   DiffServ prioritization               1997   IOS 11.0
   Tag switching (pre-MPLS)              1997   IOS 11.1
   Security – 1: Encryption, Firewalls   2000   IOS 11.2
   Security – 2: NAT                     2001   IOS 12.0
   No dramatic change in services        2007   IOS 12.4T
   offered to end-user




                                                            4
Internet Evolution (contd.)

 Common observations:
    Core features are gradually beginning to ossify
    Routers are becoming faster and more reliable

 Deployability concerns are common with most services

 All-or-nothing implementation problems
    For example, we still do not see deployment of Secure-BGP



        Need for ways to offer new services
        and enhance existing services!

                                                                 5
Overlay Networks

Overlay networking helps overcome functionality
limitations by forming a virtual network that is:
    Independent
    Customizable
 over the IP network (Native layer).




                                                    6
Example: Latency-Optimized Overlay

                    A        50ms
                                                   D

  Overlay link
                                                       Overlay nodes
                 20ms


                               20ms
                                           C
         Relaying   B


    Overlay routing is independent of native layer routing
    Each Overlay path comprises one or more Overlay links,
     based on a certain selfish objective

                                                                       7
Implementation

  Typically, we just add a new header inside
  the regular IP header

WIRE
            Ethernet      IP        TCP     Application
             header     header     header      data

            Dest B      Dest C
                       Secondary
                       IP header


  Referred to as IP-in-IP encapsulation


                                                          8
Classification of Overlay Networks

                Overlay networks




        Peer-to-peer         Routing overlay
          networks              networks
      (e.g. BitTorrent)


                   End-system               Service
                     overlays               overlays
                   (e.g. Skype)           (e.g. VINI)


                                                        9
Service Overlay Networks

Offer enhanced or new services by deploying
intelligent routing schemes.




                                              10
Service Overlay Networks (contd.)


Throughput optimized                 Latency reducing
overlay              C                   overlay
                             E   F                          OVERLAY
                                                        H    LAYER
         A               D                 G
               B



         A          C
                             E   F                      H

                                                            NATIVE IP
               B                                             LAYER

                         D
                                           G

                                                                        11
Service Overlay Networks (contd.)

 Multicast (e.g. ESM, Overcast)
 Better routes (e.g. RON, Detour, X-Bone)
 Customized forwarding (e.g. I3, Scattercast)
 QoS (e.g. OverQoS, SON)
 Security (e.g. DynaBone, SOS)
 … and much more




                                                12
Challenge 1: Functionality overlap
  Each layer performs rerouting, with no knowledge of
  which layer leads to optimal restoration
  Overlay
rerouting
                     C                             OVERLAY1
                                   E   F
                                               H    LAYER
            A              D               G
                A
                B


            A        C
                                   E   F       H

                    X Failure

                B
                                                   NATIVE IP
                           D
                                                    LAYER
                                           G


                    Native rerouting                           14
   Challenge 2: Objective Mismatch

     Conflict in objective between the two layers
                           AS policy
                           violation
                   C                           OVERLAY1
                           E      F
                                           H    LAYER
           A           D               G
               B



           A       C
PROVIDER
                           E      F        H



               B
                                               NATIVE IP
CUSTOMER               D
                                                LAYER
                                       G


                                                           15
Challenge 3: Coexistence issues
 In reality, coexistence is required between:
    overlay and legacy apps.
    overlay and other overlay apps
                   C                              OVERLAY1
                              E       F
                                              H    LAYER
         A             D                  G
              B


         A         C
                              E       F       H



              B
                                                  NATIVE IP
                       D
                                                   LAYER
                                          G

                                                              16
       Cross-Layer Interaction

Performing dynamic routing at both overlay and
native IP layers leads to:

     Functionality overlap (Both overlay layer and IP
      layer perform similar set of functions)

     Mismatch or misalignment of routing objectives

     Contention for limited physical resources



                                                         17
       Cross-Layer Interaction (contd.)

These issues are amplified in the presence of
     Selfish motives and aggressive behavior

     Lack of information about other layer

     Increasing impact ( #overlays  |Traffic| )




                                                    18
Summary of my thesis
   Overlay routing conflicts with intra-domain load balancing
    [Infocom07]

   Overlay routing conflicts with inter-domain policies
       Transit policies [ICNP06]
       Exit policies [Globecom07]

   Interaction between failure recovery at each layer
    [Infocom06]

   A framework for cross-layer cooperation
    [Hotnets05]

   Selfishness of performance-aware applications (BitTorrent)
    [under submission]

                                                                 19
A Coexistence and Conflict Issue

         Overlay routing vs
  Intra-domain Traffic Engineering
Repeated Non-Cooperative Game
Player1: Overlay Routing - Latency-optimized paths between nodes

Player2: Traffic Engineering - MPLS-based scheme that solves a
         linear program (LP) to obtain optimal load-balanced routes

                              Overlay
              Overlay Link    Routing      Overlay
               Latencies                   routes

                                                               Overlay layer
                                                                 traffic
Native link
  delays      
                                             Traffic on each
                                               overlay link


                  Native       Traffic                          Background
                  routes     Engineering   TM                    traffic



                                                                               21
Illustration of OR vs TE
                                       14ms                         C
Shortest         A                                     4ms
latency                    4ms
                                      B                                 5ms

routes                                             10ms
                                                                         D
       OVERLAY                              23ms


        NATIVE                     2
                           E     10ms
                                               F         4
                                                        2ms         C
                     3          3           4
                                             2ms               4           3
                     2ms       2ms
Minimize                                                      2ms         3ms        Numbers on
(Max util)       A                    B        5
                                                             G                H       each link
                                              4ms
                                 2                               3                  represent the
                  2                                                            3
                 3ms           3ms                               6ms          2ms     avail-bw
                           I           2           J           2
                                     10ms                                D
                                                              10ms




                               Initial State
                                                                                                    22
Illustration of OR vs TE (contd.)
                                    14ms                         C
              A                                                                   Multihop paths
                                                    6ms
                        4ms
                                   B                                  5ms          ABC
                                                10ms                               ABD
                                                                       D
    OVERLAY                              23ms


     NATIVE                     2
                        E     10ms
                                            F         4
                                                     2ms         C
                  0           0          4
                                          2ms               2               2
                  2ms       2ms                                         3ms
                                                           2ms
              A                    B        1             G                 H
                                           4ms
               2              2                                  1          2
              3ms           3ms                                 6ms         2ms
                        I           2           J           2
                                  10ms                                 D
                                                           10ms



          Overlay traffic                           Avail-bw
           introduced                               changed
                                                                                                   23
Illustration of OR vs TE (contd.)
                                     14ms                         C
               A                                                                  Multihop paths
                                                     4ms
                         5ms                                          5ms          ABC
                                    B
                                                 10ms                              ABD
                                                                       D
    OVERLAY                               23ms


     NATIVE                      2
                         E     10ms
                                             F         2
                                                      2ms         C
                   1          1           2
                                           2ms               4           2
                   2ms       2ms                                        3ms
                                                            2ms
                                             3
       SPLIT   A                    B
                                            4ms            G                H
                1              1                               1             2
               3ms           3ms                               6ms          2ms
                         I           2           J           2
                                   10ms                                D
                                                            10ms



          After TE reacts                              Latency
                                                       changed
                                                                                                   24
Illustration of OR vs TE (contd.)
                                       14ms                         C
                 A                                                                  Multihop paths
                                                       4ms
                           5ms                                          5ms          ABC
                                      B
                                                   10ms
                                                                         D
                                                                                    ABCD

    OVERLAY                                 23ms                                     BCD

     NATIVE                        2
                           E     10ms
                                               F         0
                                                         2
                                                        2ms         C
                     1          1           0
                                            2
                                             2ms               4           0
                                                                           2
                     2ms       2ms                                        3ms
                                                              2ms
                                               5
                                               3
      SPLIT      A                    B
                                              4ms            G                H
                  1              1                               31            0
                                                                               2
                 3ms           3ms                               6ms          2ms
                           I           2           J           2
                                     10ms                                D
                                                              10ms



              After Overlay                             Avail-bw
              routing reacts                            changed
                                                                                                     25
Simulation Results

TE
objective
            Round




Overlay
objective


Overall
stability

                      26
Our goal
.. is to propose strategies that

  obtain the best possible performance for a
  particular layer
  while steering the system towards a stable
  state.




                                               27
Resolving Conflict – Basic Idea
 Designate leader / follower

 Leader will act after predicting or
 counteracting the subsequent
 reaction of the follower

 Similar to the Stackelberg approach




                                       28
Resolving Conflict - Obstacles
 Incomplete information

 Unavailable relation between the objectives

 NP-hard prediction




                                               29
Resolving Conflict - Simplification
  Assume: Each layer has a general notion of the other
  layer’s selfish objective

  Operate leader such that
  a. Follower has no desire to change       Friendly
  b. Follower has no alternative to pick    Hostile


  Constitutes a preemptive action

  Use history to learn desired action gradually.


                                                         30
Overlay Strategy - Friendly
  Native layer only sees a set of src-dest demands

                                           C
               Overlay link 1   Traffic (Mbps)
       E
                 A B                 0
                     B
                 A C                 1
                 BC       1          2          D
           A



  Improve latency of overlay routes, while retaining the
  same load pressure on the native network!

 Load-constrained LP



                                                           31
Overlay Strategy – Friendly (contd.)



                          Acceptable
                          to both OR
                          and TE




                      Stable within
                      a few rounds




                                       32
Overlay Strategy - Hostile
  Push TE to such an extent that it does not reroute the
  overlay links after overlay routing

                                     C

                E               1
  Unused
  overlay                   B
  link AB
                                1        D
                    A



  Send dummy traffic in an effort to render TE
  ineffective

 Dummy traffic injection


                                                           33
Overlay Strategy - Hostile (contd.)

                                  TE can’t
                                  improve
                                  further


                     Acceptable
                     only to OR




                                             34
Native Strategy - Friendly
  TE pays no attention to the length of the route!

                                       C
   Native route   Next hop      Total Hops
    E                    1
      A B           E              2
      A C         B D              2
     DE              B             2
                          1                  D
           A
    All others    Dest itself       1




  TE should balance load, while ensuring that the path
  length is almost the same!

 Hopcount-constrained LP


                                                         35
Native Strategy - Friendly (contd.)




                             Acceptable
                             to both OR
                             and TE




                              Takes a bit
                              longer to
                              converge




                                            36
Native Strategy - Hostile
  Dissuade overlay routing from using certain multihop
  paths

    Overused
                                       C
    native link
                  E            1

                      1    B

                               1           D
                      A



  Increase latency of native links that are heavily loaded,
  without any knowledge of overlay networks

 Load-based latency tuning


                                                              37
Native Strategy - Hostile (contd.)




                                         Disrupted
                                          overlay
                                          routing




                           Takes a bit
                           longer to
                           converge



                                                     38
Preemptive Strategies: Summary
 We proposed four strategies that improve performance
 for one layer and achieve a stable operating point

 Inflation factor
 =   Steady state obj value with strategy
             Best obj value achieved
                                                      Inflation
   Leader                  Strategy               Overlay     TE
   Overlay   Friendly: Load-constrained LP         1.082    1.122
             Hostile: Dummy traffic injection      1.023    1.992
   Native    Friendly: Hopcount-constrained LP     1.027    1.184
             Hostile: Load-based Latency tuning    1.938    1.072



                                                                    39
Preemptive Strategies: Summary (contd.)

 Each strategy achieves best performance for the
 target layer
    within a few rounds
    with no interface between the two layers
    with all information inferred through simple measurements




                                                                 40
In Summary, Overlays…

 … offer valuable services needed by end-systems

 … leads to complex cross-layer interaction with
 potentially detrimental effects

 … are hard to detect, as seen from efforts with
 identifying Skype traffic




                                                   41
Future of Overlays

Overlays are essential as…
      Means for end-systems to collaborate
      Environment for testing future innovations (GENI)
      Architecture for Future Internet in the form of Network
       Virtualization


 Cross-layer interaction will affect performance. How
  best to design protocols and services in the future?




                                                                 42

								
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