1. Algorithms and Techniques in Structured Scalable Peer-to-Peer Networks
Mohammed Nadeem Ahmed
Department of Computer Science and Engineering
Professor: Dr. Gautam Das
T.A : Mr. Ashish Chawla

2. Outline What is Peer-to-Peer? Types of Peer-to-Peer Networks Chord
Unstructured P2P Networks
Napster, Gnutella & KaZaA
Structured P2P Networks
Chord
Overview & Implementation
Distributed Hash Tables
Routing in Chord
Chord Features
Chord Performance
Comparison in performances in Unstructured and Structured P2P networks

3. What is Peer-to-Peer Sharing of Free MP3 Files !! : )
Peer-to-Peer unlike Traditional Client-Server models
Scalable
Flexible
Fault-Tolerant
Easily Deployable

4. Types of Peer-to-Peer Networks
Unstructured P2P Networks
No global protocol
Maintained by a Central Server or Peer Leader
Easy to Deploy & Maintain
Poor Search Efficiency
Not Scalable

5. Types of Peer-to-Peer Systems
Structured P2P Networks
Global protocol ( Hash Functions)
High Search Efficiency
Natural Load Balancing
Highly Scalable

6. Examples of Unstructured P2P Systems
Napster
Peers update central server about Content
Peers get files by querying Central Server
File transfer directly between peers

7. Examples of Unstructured P2P Systems
Gnutella
Peers form a logical overlay network
Queries are broadcasted to neighbors
Neighbors broadcast to their neighbors (Flooding)
Query radius is limited (Not Scalable)

8. Examples of Unstructured P2P Systems
KaZaA
Hybrid approach
Concept of Peer-leaders (just like C.S in Napster)
Peer-Leaders broadcast queries to other Peer-Leaders. (just like in Gnutella)

9. Problems with Unstructured P2P
What we have?
Centralized : Napster
Table size – O (n)
Number of Hops – O (1)
Flooding of Queries : Gnutella
Table Size – O (1)
Number of Hops – O (n)

10. What we want from P2P Efficiency Scalability Robustness:
O (log (N)) messages per look up (where N is the total number of nodes in the network)
Scalability
O (log (N)) states per node
Robustness:
Ability to handle a lot of instabilities

11. Chord Overview Provides just one operation:
Lookup (key) -> Node (IP Address)
Chord is a lookup service, not a search engine.
It’s a building block for P2P applications

12. Distributed Hash Tables
The resource file (e.g. monalisa.jpg) is translated into a 160 bit identifier through the hash function SHA - 1
160 bit resource ID
Similarly the node (IP address) is also translated into a 160 bit identifier through the same function.
160 bit node ID
Node with the NodeID closest to that resource name ID is responsible for that resource.

13. Scalable Routing in Chord
Chord can scale millions of nodes
Uses Finger Tables
Each node is responsible for a bunch of nodes
In finger table row I at node n = successor (n + 2^i-1)
Finger intervals increase with distance from node n
If close, short hops
If far, long hops
Thus in a N-node network, needs to contact only O (log (N) nodes to find any node.

14. Chord Features Load Balancing Decentralization Scalability
Uses distributed Hash Function
Decentralization
No node is as important as any other
Scalability
Only uses O (log (N)) to reach N nodes
Availability
Node responsible for a key can always be found
Robustness
Minimal join/leave disruption

15. Average messages per look up
Chord Performance
Average messages per look up
Number of nodes

16. Summary: Unstructured vs Structured P2P
No global protocol used
Maintained by a C.S or Peer-Leader
All nodes need to know every other node (O (n) Look-ups)
Structured
Global protocol involved (Hash Function)
Completely Distributed
Nodes need to know only a handful of others ( O log (N) Look-ups)

17. Unstructured Vs Structured P2P Contd:
Unstable when nodes frequently join or leave.
Scalability Problems
Phrase-match queries
Structured
Stable in all conditions
Highly Scalable
Exact-Key match queries

18. Thank You