When the Squirrel peer-to-peer web caching service was evaluated by simulation, 4.11 hops were required on average to route a request for a cache entry when simulating the Redmond traffic, whereas only 1.8 were required for the Cambridge traffic. Explain this and show that it supports the theoretical performance claimed for Pastry.

Answer:An external caching scheme stores copies of web objects

or meta-data so that clients can avoid requests to a web

server. The best known example of an external cache is a

web proxy, but with the rapid spread of web technologies,

many other caching scenarios can be identified. Caching

is central to performance in the web, both because it re-

duces load on servers, and because cached data is normally

cheaper to access from another machine that is closer in the

network. Although cooperation between cache managers is

not a common feature of existing web architectures, coop-

erative caching supported by peer-to-peer architectures has

great potential [9, 13]. When sets of client systems have sim-

ilar interests and fast low-latency interconnections, shared

caching could bring significant benefits.

The peer-to-peer mechanisms referred to