This document discusses different types of peer-to-peer network architectures including client-server, pure peer-to-peer, and hybrid peer-to-peer. It describes key characteristics of peer-to-peer networks such as nodes acting as both clients and servers, a lack of centralized control, and dynamic membership. Examples of early peer-to-peer systems like Napster and Gnutella are provided along with structured peer-to-peer approaches like Chord and BitTorrent. Research areas related to peer-to-peer networks like resource discovery, efficiency, robustness, incentives, and security are also summarized.

1. CS254: Network TechnologiesCS254: Network Technologies
Peer to Peer NetworksPeer to Peer Networks
James Salter
j.salter@surrey.ac.uk
16 November 2004

2. Client/Server ArchitectureClient/Server Architecture
 Clients send requests
to/via a central server
 Small #messages
 Single point of failure

3. Pure Peer-to-Peer ArchitecturePure Peer-to-Peer Architecture
 Resilient
 Large #messages
 No central server
 Clients connected to
one or more peers

4. Hybrid Peer-to-Peer NetworksHybrid Peer-to-Peer Networks
 Some nodes act as group managers/routers
 More robust than client/server
 Potentially lower #messages than pure P2P

5. Characteristics of a P2P NetworkCharacteristics of a P2P Network
 Nodes can act as clients and servers
 No centralised server/authority
 (in pure P2P networks)
 Network is highly dynamic
 Nodes join and leave regularly
 Large-scale
 Potentially millions of nodes
 Nodes are autonomous
 But co-operate to share/retrieve resources

6. Networking at the Application LayerNetworking at the Application Layer

7. OverlaysOverlays
 Creates a virtual network: network
overlay
 Connections between nodes defined by
application, not by wires
 Overlay can have little relation to
underlying network connections
 Needlessly send data across the Internet
instead of through a LAN?

8. Napster (1999-2002)Napster (1999-2002)
File
Transfer

9. GnutellaGnutella

10. The ProblemThe Problem
 Scalability
 Napster: central server is a bottleneck
 Gnutella: large volumes of query traffic
 Number of Messages
 Gnutella: query must be sent to every node
 Fault Tolerance
 Napster: single point of failure
 Ability to Find Resources
 Gnutella: query horizon (TTL limit)

11. Gnutella2Gnutella2

12. Structured P2PStructured P2P
 Avoid random visiting of nodes to find
content
 Utilise an index similar to Napster
 Split index and distribute over entire
network
 Must know where to find each piece of
the index – organisation of nodes
 More efficient (less hops): requests
always routed towards content

13. Structured P2P: ChordStructured P2P: Chord
 Each node has a unique ID number
 File names hashed to
generate file ID
 Files hosted on node
with closest ID
 Searching: hash file
name to give ID of
node hosting file
 Small routing costs
1
41
7
22
28
34
48
52
70
73

14. BitTorrentBitTorrent
Tracker
Seed
.torrent

15. P2P ApplicationsP2P Applications
 File sharing
 Distributed computing
 Instant messaging
 Media streaming/distribution
 Web services
 Workgroups
 Networked devices

16. Research AreasResearch Areas
 Resource discovery/searching
 Efficiency, more powerful queries
 Robustness/stability
 Can the network operate under high churn?
 Incentives
 Why should I provide as well as consume?
 Reputation/Quality
 How good/reliable are peers in the network?
 Security
 Malicious/suicidal peers, attacks on the network