Peer to Peer Overlay Routing Concepts

Speaker: Vasileios Komianos

Supervisor: Konstantinos Oikonomou

Ionian University, Dept. of Informatics, Postgraduate

For the course: Distributed Networks & Algorithms

Peer to Peer Networks

• The opposite of client - server architecture.

• Distributed systems.

• Most famous: Napster, Gnutella.

Why Overlay?[1]

• It resides on the application layer.

• IP is not focused on peer-to-peer networks.

• It does not represent the network’s physical topology.

• Depending on the implementation it can address more objects than IPv4.

What DHT is?DHT stands for Distributed Hash Tables, imagine a suitable for p2p nets phone book.

A file’s or service’s name, from now on called GUID* or key, is being hashed and stored on the DHT. Each GUID is associated with a node’s IP.

*Globally Unique Identifier

The Chord Case[2]

Scalable p2p lookup service:

• Load balance

• Decentralization

• Scalability

• Availability

• Flexible naming

The Chord Case

Chord Overlay Topology:Virtual Overlay Circle

DHT is replaced by finger table.

Finger table represents a part of Chord’s topology.

Each Chord node needs routing information about only a few nodes.

Node position depends on it’s key.

Each node is responsible for keys having lower than it’s key value and greater than this of the previous node.

To be continued…

References

[1] George Coulouris, Jean Dollimore, Tim Kindberg(2005). Distributed Systems: Concepts and Designs, fourth edition. Addison-Wesley.

[2] Ion Stoica, Robert Morris, David Karger, M. FransKaashoek, Hari Balakrishnan: Chord: A scalable Peer-to-peer Lookup Service for Internet Applications. In Proceedings of ACM SIGCOMM 2001 (San Diego, California, USA, August 27-31).

Bibliography[1] Konstantinos Oikonomou, Spyros Sioutas, Ioannis

Stavrakakis: Scalable Communication Cost Reduction: The Chord Case. In Ad Hoc Networking Workshop, 2009. Med-Hoc-Net 2009.