ALTO+Scribe

The idea

  • The research on the topology-aware peer-to-peer applications (cf. P4P, Oracle, ALTO) generally focuses on optimal peer selection in BitTorrent, an unstructured file-sharing system.
  • Application-level multicast systems optimise their traffic e.g. by measuring round-trip time.
  • Is it possible to optimise the ALM-related traffic by the means developed for the file-sharing systems?

FreePastry modifications

  • Exchange some of the routing table entries with neighbours.
  • Cache the (NodeHandle,NetworkAddress) pairs.
  • Sort the network addresses using the ALTO protocol.
  • Insert the most optimal peers’ handles into the routing table.
  • Force Scribe to resubscribe when the process finishes and the route has changed.

Simulation preparation

Underlying network model

Transit-stub network model

Routing: OSPF, BGP.

Overlay network

  • 1995 (on average) FreePastry nodes after the warm-up.
  • One Scribe topic (multicast group).
  • All peers subscribe to the topic.

Scenarios

  • ALTO popularity:
    • client probability = 0%, server probability = 0%;
    • client probability = 25%, server probability = 100%;
    • client probability = 50%, server probability = 100%;
    • client probability = 75%, server probability = 100%;
    • client probability = 100%, server probability = 25%;
    • client probability = 100%, server probability = 50%;
    • client probability = 100%, server probability = 75%;
    • client probability = 100%, server probability = 100%.
  • Routing table rows exchanged:
    • 1,
    • 2,
    • 4.
  • Each scenario run 30 times.

Simulation results

Multicast traffic

Global traffic

Server popularity = 100% Client popularity = 100%

Incoming transit traffic

Server popularity = 100% Client popularity = 100%

Outgoing transit traffic

Server popularity = 100% Client popularity = 100%
Zoom

Peering traffic

Server popularity = 100% Client popularity = 100%
Outgoing
Incoming

Local traffic

Server popularity = 100% Client popularity = 100%

Maintenance traffic

ALTOQuery, ALTOResponse

Server popularity = 100% Client popularity = 100%
Local traffic

RequestRouteRow

Server popularity = 100% Client popularity = 100%
Global traffic
Outgoing transit traffic

BroadcastRouteRow

Server popularity = 100% Client popularity = 100%
Global traffic
Incoming transit traffic

SubscribeMessage

Server popularity = 100% Client popularity = 100%
Global traffic
Incoming transit traffic
Peering traffic
Outgoing
Incoming

Total traffic

I.e., multicast traffic + maintenance traffic.

Relative delay penalty

In domains without ALTO server In domains with ALTO server

Publications

The results were presented in:

  • P. Wydrych and P. Chołda, “ISP-supported traffic reduction for application-level multicast,” (presentation) in Proc. IEEE Int Communications (ICC) Conf, Kyoto, Japan, Jun. 2011. ©IEEE, available on IEEE Xplore.

    The paper proves that it is possible to optimize application-level multicast operation from the viewpoint of traffic flows. A modification of the FreePastry/Scribe application is proposed to enable cooperation with the IETF ALTO (Application- Layer Traffic Optimization) protocol. Consequently, the overlay topology is constructed taking into account the underlying network topology. The presented results show that costly traffic types can be reduced while the increase of the delay is not harmful.

  • P. Wydrych, “Analysis of practical issues related to routing in overlay networks,” Master’s thesis, Department of Telecommunications, AGH University of Science and Technology, Kraków, Poland, Sep. 2009.

    Since the introduction of Napster in 1999, many peer-to-peer (P2P) systems have been designed. In the beginning they were used for file-sharing, but then the ideas developed during the research of file-sharing overlay systems were employed in other fields. The application-level multicast (ALM) systems became an important alternative to client-server streaming and IP multicast. Since the peer-to-peer client applications became very popular and they build their structures without taking into account the underlying network topology, they cause the enormous percentage of the inter-domain traffic. Therefore, the idea of cooperation of peer-to-peer application users and network operators have emerged. At the time of writing, the research on the P2P-ISP collaboration focuses on the optimisation of the traffic generated by unstructured file-sharing systems.

    This thesis proves that the solutions developed by the ALTO group can be successfully employed to reduce the traffic generated by the application-level multicast systems built on top of structured overlay networks.

Acknowledgements

I would like to thank Dr. Piotr Chołda and Dr. Rafał Stankiewicz for their advices.