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Proxy server and bandwidth reduction

Short answer

A proxy caches web objects and serves hits locally, so access-link traffic becomes request rate times object size times the miss rate. With 15 Mbps load, no proxy gives 15 Mbps or 100% utilization, a 40% hit rate gives 9 Mbps or 60%, and a 70% hit rate gives 4.5 Mbps or 30%.

Explain how the proxy server reduces the use of access network bandwidth. Illustrate your answer with appropriate figure.

A proxy server (web cache) is an intermediate server between the clients of an institution and the Internet. The browsers are configured to send all HTTP requests to the proxy. It stores copies of recently requested objects, and so reduces the traffic on the access link (the link between the institutional network and the Internet).

Working

  1. The client sends the request to the proxy.
  2. Cache hit: the proxy has the object, so it returns it directly from its disk. No traffic crosses the access link.
  3. Cache miss: the proxy requests the object from the origin server, stores a copy and forwards it to the client.
  4. The proxy checks freshness with a conditional GET (If-Modified-Since); if the object has not changed, the origin replies 304 Not Modified with no body, saving bandwidth.
 Institutional network                       Internet
 +----+                                  +--------------+
 |PC 1|--+                               | Origin server|
 +----+  |   LAN 100 Mbps   access link  +--------------+
 +----+  +--[ Proxy ]=====( 15 Mbps )======
 |PC 2|--+     (cache)
 +----+

Numerical illustration

Average object size = 1 Mbit, request rate = 15 requests/s from the LAN.

CaseTraffic on access linkUtilisation of 15 Mbps link
No proxy15 × 1 = 15 Mbps100 % (long delays)
Proxy with 40 % hit rate0.6 × 15 = 9 Mbps60 %
Proxy with 70 % hit rate0.3 × 15 = 4.5 Mbps30 %

The access link need not be upgraded, response time falls (local LAN speed for hits) and queueing delay drops sharply.

Other benefits

Lower cost, less load on origin servers, content filtering and access control, logging.

✓ Answer checked by Claude Opus 5.5 (high effort)

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