This document summarizes Content Addressable Network (CAN), a structured peer-to-peer network. CAN partitions a virtual d-dimensional space among nodes, with each node responsible for a zone. It allows keys to be mapped to values by hashing keys to points in the space. New nodes join by contacting an existing node and splitting its zone. Routing is done by forwarding requests to the node responsible for the zone containing the destination point. Zones are reassigned if neighboring nodes fail to send periodic alive messages. CAN scales well as routing path length increases slowly with number of nodes. Future work could involve increasing dimensions, caching, and zone overloading.

1. Amit Singh Dahal
g5638545
Content Addressable
Network(CAN)
Structured P2P Network

2. Outline
 Introduction
 Overview
 Construction
 Routing
 Maintenance
 Evaluation
 Future Improvements

3. Introduction
 one of the original four distributed hash table
proposals, introduced concurrently with
Chords, Pastry, and Tapestry.
 developed at UC Berkeley
 CANs overlay routing easy to understand
 scalable indexing system for large-scale
decentralized storage applications
 has a good performance

4. Overview
 distributed, decentralized P2P infrastructure
system that maps keys onto values
 keys hashed into d dimensional Cartesian space
 Interface:
 insert(key, value)
 retrieve(key)
 associate to each node and item a unique
coordinate in an d-dimensional Cartesian space

5. Overview
 entire space is partitioned amongst all the nodes
 every node “owns” a zone in the overall space
 can store data at “points” in the space
 can route from one “point” to another
 point  node that owns the enclosing zone

6. Overview
y
x
State of the system at time t
Node
Resource
Zone
Fig:2 dimensional space with a key mapped to a point (x,y)

7. Construction
Bootstrap
node
new node

8. Construction
I
Bootstrap
node
new node 1) Discover some node “I” already in CAN

9. Construction
2) Pick random point in space
I
(x,y)
new node

10. Construction
(x,y)
3) I routes to (x,y), discovers node J
I
J
new node

11. Construction
newJ
4) split J’s zone in half… new owns one half

12. Routing
 data stored in the CAN is addressed by name
(i.e. key), not location (i.e. IP address)
 have some routing mechanism
 A node only maintains state for its immediate
neighboring nodes

13. Routing
y
Node
M(x,y)
N(x,y)
 d-dimensional
space with n zones
where d=2 and n=8
2 zones are
neighbor if d-1 dim
overlap
Algorithm:
Choose the neighbor
nearest to the
destination
M(x,y) Query/
Resource
key

14. Maintenance
 Use zone takeover in case of failure or leaving of
a node
 Send your neighbor table update to neighbors to
inform that you are alive at discrete time interval t
 If your neighbor does not send alive in time
t, takeover its zone
 Zone reassignment is needed

15. Evaluation
 Scalability
-For a uniformly partitioned space with n
nodes and d dimensions:
* per node, number of neighbors is 2d
*average routing path is (d*n1/d)/3
hops (due to Manhattan distance
routing, expected hops in each
dimension is dimension length * 1/3)
*Can scale the network without
increasing per node state
 Robustness
-no single point of failure

16. Future Improvements
 Multi-dimension
-increase in dimension reduces path length
 Caching and replication techniques for better
performance
 Overloading the zone
-increases availability, reduces path
length, reduces per hop latency
 Uniform partitioning
-compare the volume of the zone with its
neighbors
-partition the zone having largest volume

17. THANK
YOU!!! 