Consider an institutional network on which there is a web pr

Consider an institutional network on which there is a web proxy server. The users on the network collectively generate 25 requests per second. The average size of requested objects is 12,500 bytes. The hit ratio for the proxy cache is 50%. The RTT to send a request and get a response from a user node on the institutional network to the proxy server is 100 milliseconds (1 milliseconds = 10-3 seconds). The RTT from the proxy server into the Internet and back is 2 seconds. a-What is the average delay to service a request? b-How big, in terms of bits per second, will the flow of requested objects coming into the institutional network from the Internet be?

Solution

Solution: Proxy server goal is satisfy client request without involving origin server.

all HTTP requests sent to proxy.if proxy has fresh copy of requested page,it returns stored copy.if not, it sends its own GET request to retrieve page from “origin server”, sends page to client and stores a copy.

Two main benefits
1. reduces web traffic over access link
2. reduces response time and load on origin servers

cache acts as both client and server.server for original requesting client .client to origin server.

why web caching:

1.reduce response timefor client request.

2.reduce traffic on an institution’s access link.

3.Internet dense with caches: enables “poor” content providers to effectively deliver content.

Definition of RTT (round trip time): time to send a small packet to travel from client to server and back.

Response time: one RTT to initiate TCP connection .one RTT for HTTP request and first few bytes of HTTP response to return.file transmission time=2RTT+Transmit time.