super-peer network. motivation: search in p2p centralised (napster) flooding (gnutella) essentially...
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Super-peer Network
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Motivation: Search in P2P
Centralised (Napster)Flooding (Gnutella)
Essentially a breadth-first search using TTLs
Distributed Hash Tables
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But….all peers are not equal
20% peers have a latency of at most 70ms and 20% have a latency of at least 280ms
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Basic Idea
Real-World P2P systems for the open Internet are heterogeneousPeer resources (Bandwidth, CPU, Memory)Peer session-time
Use Peers with better “characteristics” to provide services to other peers in the system
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Super-Peer Definition
A super-peer is a node in a peer-to-peer network that operates both as a server to a set of clients, and as an equal in a network of super-peers. [Yang/Molina '03]
Super-peers have high utility relative to non super-peers, where higher utility peers are “better” at providing superpeer service(s).
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Super-Peer Networks
Exploit heterogeneity in P2P Networks by using higher utility peers to provide services
A super-peer network operates exactly like a pure P2P network, and each super-peer is connected to a set of clientsClients are connected to a single super-peer
only
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Super-Peer Architecture
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Super peer network
ClusterA super-peer and its clients
Cluster sizeNumber of nodes in the cluster, including the
super-peer itselfA pure p2p network is actually a
“degenerate” super-peer network where cluster size is 1Every node is a super-peer with no clients
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Super peer network
Super-peer keeps an index over its clients’ dataJoints
Client sends metadata over its collection to its super-peer
Updates
Query processingClient -> super-peerSuper-peer -> neighbors (super-peer)
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Super-Peer Design Issues
What services do super-peers provide? Ordinary peer to super-peer connections
Redundancy, Performance, Fairness
Super-Peer Connection Topology Super-peer promotion
Which/how many peers should be super-peers?
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What Services do Super-Peer Systems provide?
File Naming/Retrieval Kazaa E-Donkey
Voice Over IP (VoIP) Skype
Anything you want!
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Ordinary Peer to Super-Peer ConnectionsA super-peer become a single point of
failure for its cluster and a potential bottleneck
To provide reliability to the clusterK-redundant
Clients send queries in a round-robin fashion
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Ordinary Peer to Super-Peer (SP) Connections
A k-redundant super-peer has much great availability than a single super-peer, howeverThe aggregate cost of a client joint action is k
times greater than beforeThe number of open connections amongst
super-peers increases by a factor of k2 !Super-peer redundancy has the surprising
effect of reducing load on each super-peer, in addition to providing greater reliability
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Super-Peer Connection Topology
The type of intra-SP topology affects the type of distributed services they provide
Random NetworkFlooding, Random Walk
DHT (don't know of any systems that do this)
Gradient TopologyGradient search
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Search in Random andGradient SP Topologies
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Super-Peer Promotion
Options:1. Promote peers that meet local utility
requirements2. Promote the top 'X' percent of peers with
highest utility (requires global knowledge of peer utility distribution)
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Super-Peer Promotion usingLocal Knowledge
Promotion algorithm makes a local decision about promotion using:Measurements of the peer’s local utility levels
for Bandwidth, CPU, MemoryA Model of Peer Utility Distributions
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Super-Peer Election using Global Knowledge
Too expensive solutionsCentralized ServersClassic Election Algorithms
Gossiping / AggregationUsed by Gradient Topology
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Conclusion
A combination of the centralized client-server model (efficiency) and distributed search (load balancing and robustness)