---
title: "Proxy server and bandwidth reduction"
subject: "Computer Networks and Security"
chapter: 6
key: "semester_7/computer_networks_and_security:proxy-server-bandwidth"
source: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/proxy-server-bandwidth
site: BCT Engineering
---

# Proxy server and bandwidth reduction

Computer Networks and Security · Chapter 6: Application Layer

- Asked in: 2070 Asar, 8 marks
- Video: [Proxy Server Explained, How Proxy Servers Work and Speed Up Browsing | TechTerms](https://www.youtube.com/watch?v=yKMyk2lllbw) — TechTerms
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/proxy-server-bandwidth
- Whole chapter: https://www.bctengineer.com/md/semester_7/computer_networks_and_security/chapter-6

## Question

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

## 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%.

## Answer

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.

```text
 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.

| Case | Traffic on access link | Utilisation of 15 Mbps link |
|---|---|---|
| No proxy | 15 × 1 = 15 Mbps | 100 % (long delays) |
| Proxy with 40 % hit rate | 0.6 × 15 = 9 Mbps | 60 % |
| Proxy with 70 % hit rate | 0.3 × 15 = 4.5 Mbps | 30 % |

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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. On a cache hit the proxy:
   A. Forwards to origin
   B. Returns object from its disk with no traffic on the access link
   C. Rejects it
   D. Updates DNS
   Answer: B. No access link traffic for hits. (Key point: Cache hit)

2. What does If-Modified-Since with a 304 response achieve?
   A. Sends the object twice
   B. Confirms freshness with no body, saving bandwidth
   C. Deletes the object
   D. Encrypts it
   Answer: B. 304 Not Modified carries no body. (Key point: Conditional GET)

3. 15 requests/s of 1 Mbit with 70% hit rate: traffic on access link?
   A. 15 Mbps
   B. 9 Mbps
   C. 4.5 Mbps
   D. 10.5 Mbps
   Answer: C. 0.3 x 15 = 4.5 Mbps. (Key point: Calculation)

4. On a cache miss the proxy:
   A. Fetches from origin, stores a copy and forwards it
   B. Returns an error
   C. Drops request
   D. Asks the client
   Answer: A. It requests from origin and caches the copy. (Key point: Cache miss)

## Related in Computer Networks and Security

- [Client-server vs peer-to-peer](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aclient-server-vs-p2p) — Computer Networks and Security, chapter 1
- [Web and file server communication](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aweb-file-server-communication) — Computer Networks and Security, chapter 6

## Related in other subjects

- [Medium network design issues and proxy servers](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Adesign-medium-network-proxy) — Internet and Intranet, chapter 5
- [Proxy array load balancing types for big ISP](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Aproxy-array-lb-mechanisms-isp) — Internet and Intranet, chapter 5
- [How transformation reduces design steps; band stop design](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Abandstop-design-steps-reduction) — Filter Design, chapter 3
- [Redundant hierarchical network design for bank](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Aredundant-network-bank-four-departments) — Internet and Intranet, chapter 5