Can Network Coding Help in P2P
Networks?
Dah Ming Chiu, Raymond W
Yeung, Jiaqing Huang and Bin Fan
Chinese University of Hong Kong
Presented by Arjumand Younus
Outline
• Introduction to Network Coding – Exploring the
Basics
• Benefits of Network Coding
• Motivation for this Study – Network Coding in
P2P Networks
• Paper Contribution
• Investigating Throughput with Network Coding
in a P2P Model
• Conclusion
Network Coding – An Introduction
• New research area with interesting applications
in practical networks.
• Mixing of data at intermediate network nodes.
• Performing arbitrary mappings on contents of
packets rather than restricted functions of
replication and forwarding.
Network Coding Basics
• Assumption behind traditional network traffic
▫ Information is separate, although it may share
network resources. (say, cars in highways or fluids
in pipes).
▫ Network coding breaks this assumption.
• A technology to combine several data packets
into one or several output packets.
An Illustration to Explain Network
Coding
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a or b?
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How to send 2 pieces of data a and b to nodes Y and Z
simultaneously?
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Benefits of Network Coding
• Throughput
• Wireless Resources
• Security
Motivation – What about Network
Coding in P2P networks
• Scalable content distribution – employs P2P
instead of network multicast.
▫ e.g. BitTorrent
• Recent Question/Debate [12] in Research
Community:
▫ Is network coding really feasible for
P2P Networks?
▫ Debate stirred up after well publicized study
Avalanche[11] by Microsoft Research
Network Coding in P2P Systems – A
Brief Look
• Without a global coordinated scheduler
• Node B, receiving Packet 1 or 2 from Node A?
Paper Contribution
• Studying benefits of network coding in P2P
systems using star network model.
• Previous Work
▫ Previous studies have been conducted but this
assumes coding at peers and no multicast in
network.
▫ Much closer to a P2P system.
Star Network Model
• Uplink sharing model (only uplinks can be bottlenecks).
• Peer cannot multicast to multiple other peers at the same
time.
Obtainable Throughput with Routing
• The main constraints to throughput are
downlink of the server and the uplinks of the
peers [13]:
• Max Throughput = min {C0, (C0+∑jC j)/n}
Impact of Network Coding on
Throughput in P2P File Sharing– Case 1
• Throughput = C0
• C0 is the minimum cut for each peer so network
coding cannot help in improving this bound.
Impact of Network Coding on
Throughput in P2P File Sharing– Case 2
• When C0≥C/n-1
▫ For throughput of X peer must receive content at
rate of Y≥X from the server or other peers.
▫ Network does not do multicasting but only
forwarding.
▫ Total capacity to satisfy all peers is C0+C < nC0 so
split amongst n peers so maximum throughput is
(C0+C)/n.
Conclusion - 1
• We demonstrated that the maximum achievable
throughput by a P2P system in a network
without multicasting is exactly the same with or
without any form of network coding.
• P2P network with Network Coding could be even
worse than BitTorrent network
Conclusion - 2
• There are several encountering difficulties for
Network Coding in P2P networks:
▫ One peer may need to spend a huge amount of
time on decoding data they receive
▫ The resources (CPU, etc. ) one needs to spend on
decoding
▫ How to ensure the uniqueness coefficients when
there are a lot of file pieces in the transferred file
▫ The topology of a P2P network is changing
▫ Peers may depart the network any time they want
However, Positive Side
• To achieve maximum throughput w/o network
coding requires very careful scheduling of other
peers exchange content.
• With network coding, this scheduling task might
be much relaxed.
Thank You
• Questions?