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					        Drafting Behind Akamai
  (Travelocity-Based Detouring)

          Aleksandar Kuzmanovic
          Northwestern University

          Joint work with:
          A. Su, D. Choffnes, and F. Bustamante

          To appear in Sigcomm 2006


http://www.cs.northwestern.edu/~akuzma/
          Drafting Behind Akamai

     Drafting




                                                   Detour




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A. Kuzmanovic             Drafting Behind Akamai
          Motivation


                Overlay networks
                – Can’t change IP, so change the layers above
                – E.g., end-point multicast


                Common problem
                – Build the “view” of the underlying network
                – Passive and active measurements




                                                                3
A. Kuzmanovic                       Drafting Behind Akamai
          Problem
                Independent measurements
                – Redundant
                – Non-scalable
                – Can cause problems
                   • E.g., synchronization


                Common service needed
                – Knowledge plane - MIT
                – A routing underlay for overlays - Princeton
                – Network Weather Service - Berkeley


                                                                4
A. Kuzmanovic                         Drafting Behind Akamai
          Our Approach
                Fact
                – CDNs (e.g., Akamai) perform extensive network
                  and server measurements
                   • Publish the results through DNS over short time scales


                Can overlay networks reuse measurements
                collected by production CDNs?
                – Significantly reduce the amount of measurements
                  (a complementary service)
                – No new infrastructure need to be deployed
                – Inherit the robustness of DNS
                – Easy integration with existing systems


                                                                              5
A. Kuzmanovic                         Drafting Behind Akamai
          CDN-Driven One-Hop Source Routing

                                                                      D



                A1
                     E1


                                  A2
                                            E2


                                                            An

          S                                                      En


                     DNS Server
                                                                          6
A. Kuzmanovic                      Drafting Behind Akamai
          Key Questions
                How does Akamai work?
                – DNS translation
                – How many web replicas does a client see?
                – Impact of different sites (e.g., Yahoo vs. NY
                  Times)?
                – DNS redirection dynamics?
                – Network or server latency?
                An example application: one-hop source
                routing
                – Mapping CDN servers to overlay nodes
                – Low-overhead protocols for exploiting CDN
                  redirections


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A. Kuzmanovic                       Drafting Behind Akamai
          DNS “Black Magic”

                                          Root DNS Server
                                                                       Akamai High-Level
                                                                          DNS Server
                 Top-Level Domain
                    DNS Server                    www.pcworld.com
                                         www.pcworld.com
                              CNAME:                     a1694.g.akmai.net
                         images.pcworld.com
                           www.pcworld.com
                          a1694.g.akamai.net
                                                                                    Akamai Low-Level
                                                             a1694.g.akmai.net DNS Server
        PCWorld Authoritative
                                                              2 ip addresses of
                                            Local DNS Server Akamai Edge Servers
            DNS Server
                                                          2 ip addresses of
                                images.pcworld.com       www.pcworld.com
                                                         Akamai Edge Servers


                                                                                        Akamai
          PCWorld                                                                     Edge Server
         Web Server
                                                    Web
                                                    Client

                                                                                                       8
A. Kuzmanovic                                 Drafting Behind Akamai
          Measuring Akamai
                2-months long measurement
                140 PlanetLab (PL) nodes
                 – 50 US and Canada, 35 Europe, 18 Asia, 8 South
                   America, the rest randomly scattered
                Every 20 sec, each PL node queries an
                appropriate CNAME for
                 – Yahoo, CNN, Fox News, NY Times, etc.


                                                     Akamai
                                                  Edge Server 1
                Akamai Low-Level                                         Akamai
                   DNS Server                                         Edge Server 2
                                                                                          .……
                                                                                   Akamai
                                   PL Node                                      Edge Server 3
                                                                                                9
A. Kuzmanovic                                Drafting Behind Akamai
          Initial Results

                Berkeley                                    Purdue
                  day




                           night


                                                                     10
A. Kuzmanovic                      Drafting Behind Akamai
          Server Diversity for Yahoo


                        Majority of PL nodes
                        see between 10 and 50
                        Akamai edge-servers



                                                               Nodes far away
                                                               from Akamai
                                                               hot-spots




                Good overlay-to-CDN
                mapping candidates                                              11
A. Kuzmanovic                         Drafting Behind Akamai
          Multiple Akamai Customers


                                Yahoo and NYTimes are
                                not hosted in U. Oregon




                                                            Amazon is not hosted
                                                            on UMass and LBNL




                FEMA is poor!
                                                                                   12
A. Kuzmanovic                      Drafting Behind Akamai
          Redirection Dynamics



                Berkeley                             Brazil




                                                    Korea




                                                              13
A. Kuzmanovic              Drafting Behind Akamai
          Key Questions
                How does Akamai work?
                – DNS translation
                – How many web replicas does a client see?
                – Impact of different sites (e.g., Yahoo vs. NY
                  Times)?
                – DNS redirection dynamics?
                – Network or server latency?
                Potentials for one-hop source routing?
                – Mapping CDN servers to overlay nodes
                – Low-overhead protocols for exploiting CDN
                  redirections

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A. Kuzmanovic                       Drafting Behind Akamai
          Methodology


                                                        10 Best
                                                        Akamai
                                                      Edge Servers



                           ………




        Akamai Low-Level
           DNS Server
                           Planet Lab Node
                                                                     15
A. Kuzmanovic                Drafting Behind Akamai
          Do CDN redirections correlate to network
          latencies? (1)
                Rank = r1+r2-1
                – 16 means perfect correlation
                                                                MIT and Amsterdam
                – 0 means poor correlation                          are excellent




                            Brazil is poor




                                                                                    16
A. Kuzmanovic                          Drafting Behind Akamai
          Do CDN redirections correlate to network
          latencies? (2)
                70% paths are
                among best 10%




                    97% better than
                    average

                                              CNN is poor!




                                                               17
A. Kuzmanovic                         Drafting Behind Akamai
          Akamai-Driven One-Hop Source Routing
          Redirections driven by
            network conditions
                                                                           D
                                                  Potential for
                                             CDN-to-overlay mapping

                 A1
                       E1


                                    A2
                                              E2


                                                                An

          S                                                           En
                                     Redirection dynamics
                                     sufficiently small for
                       DNS Server      network control
                                                                               18
A. Kuzmanovic                        Drafting Behind Akamai
          Methodology

                                    Akamai path 1

                                          Akamai path 2                        Destination
                                                         Akamai path 3

                Akamai path 1
                                                                   Akamai path 10
                         Akamai path 2


                                                                               Direct Path
                                   Akamai path 3
    Akamai Low-Level
       DNS Server
                                         Akamai path 10




                          Source
                                                                                             19
A. Kuzmanovic                             Drafting Behind Akamai
          Akamai-driven source routing (1)

                  Taiwan-UK                            UK-Taiwan




                80% Taiwan
                15% Japan                              75% U.K.
                5 % U.S.                               25% U.S.




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A. Kuzmanovic                 Drafting Behind Akamai
          Akamai-driven source routing (2)

           Experiment: US (6), Europe (3), S. America (2), Asia (3)




                                                                              25% of Akamai
                                                                              paths better than
                                                         Akamai and direct    direct paths
                                                         paths have similar
                    Direct paths better                  performance
                    than Akamai paths




                                                                                                  21
A. Kuzmanovic                             Drafting Behind Akamai
          Path pruning
                Fact
                – Not always is Akamai-driven path better than the
                  direct one


                Practical issues
                – How frequently to make a decision whether to use
                  the direct or the Akamai path?
                – Should one use
                   • the first (of the 2 paths) returned by Akamai (FAS)
                   • the better (of the 2 paths) returned by Akamai (BTAS)




                                                                             22
A. Kuzmanovic                         Drafting Behind Akamai
          Path Pruning Result



                           BTAS better than FAS


                                                             2 hours update frequency
                                                          before the performance declines
                Direct path accounts for
                    78% of the gain




                                                                                            23
A. Kuzmanovic                              Drafting Behind Akamai
          Conclusions
                Reuse measurements performed by CDNs
                Reverse-engineering Akamai
                – DNS redirections sufficiently small
                – Strong correlation to network conditions
                – All clients see a large number of paths
                CDN-driven one-hop source routing
                – 25% of Akamai paths outperform direct paths
                – 50% of nodes “discovered” by Akamai outperform
                  direct paths
                – Low-overhead pruning algorithms
                Global Internet “weather-report” service for
                little to no cost

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A. Kuzmanovic                      Drafting Behind Akamai

				
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