Client-Server and Peer-to-Peer Networks

This lesson covers the two main network models — client-server and peer-to-peer (P2P) — as specified in OCR J277 Section 1.3.1. You need to understand how each model works, its advantages and disadvantages, and when each is appropriate.

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Client-Server Networks

What Is a Client-Server Network?

In a client-server network, there is one or more central servers that provide services and resources to multiple clients (user devices). The server manages shared resources and controls access.

How It Works

Component	Role
Server	A powerful computer that stores files, manages access, runs services (email, web, print), and controls security
Client	A user's computer that requests services or data from the server

Process:

1. A client sends a request to the server (e.g. "I want to open my file").
2. The server processes the request (e.g. checks permissions, locates the file).
3. The server sends a response back to the client (e.g. the requested file).

Types of Server

Server Type	Function
File server	Stores and manages shared files
Print server	Manages print jobs sent to shared printers
Email server	Sends, receives, and stores emails
Web server	Hosts websites and serves web pages
Database server	Manages shared databases
Authentication server	Manages user login credentials and access permissions

Advantages of Client-Server

Advantage	Explanation
Centralised management	Files, users, and security are managed from one place
Centralised backup	The server can be backed up regularly and automatically
Security	User permissions and access rights are controlled centrally
Scalability	New clients can be added easily
Resource sharing	Printers, files, and internet connections are shared efficiently

Disadvantages of Client-Server

Disadvantage	Explanation
Cost	Servers are expensive to buy and maintain
Specialist staff	A network administrator is needed to manage the server
Single point of failure	If the server fails, all clients lose access to shared resources
Congestion	If too many clients request services simultaneously, the server may slow down

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Peer-to-Peer (P2P) Networks

What Is a Peer-to-Peer Network?

In a peer-to-peer network, there is no central server. Every device (called a peer or node) is equal — each device can act as both a client and a server, sharing its own files and resources directly with other devices.

How It Works

• Each computer stores its own files and manages its own security.
• Any device can share files directly with any other device on the network.
• There is no centralised control — each user is responsible for their own device.

Advantages of Peer-to-Peer

Advantage	Explanation
Low cost	No expensive server hardware needed
Easy to set up	Does not require specialist knowledge
No single point of failure	If one device fails, others continue working
No dependency on server	Users are not reliant on a central server being available

Disadvantages of Peer-to-Peer

Disadvantage	Explanation
No centralised management	Each device must be managed individually
No centralised backup	Each user must back up their own files
Security	Harder to enforce consistent security policies across all devices
Scalability	Performance degrades as more devices are added
Availability	Files stored on a peer are only available when that peer is online

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Comparing Client-Server and Peer-to-Peer

Feature	Client-Server	Peer-to-Peer
Central server	Yes	No
Management	Centralised	Decentralised
Backup	Centralised	Each user's responsibility
Security	Controlled centrally	Each user manages their own
Cost	High (server + admin)	Low
Scalability	Good	Poor (degrades with more peers)
Best for	Schools, businesses, large organisations	Small home networks, file sharing

flowchart TB
  subgraph CS[Client-Server]
    direction TB
    SRV["(Central Server<br/>files, auth, backup)"]
    C1[Client 1] -->|request| SRV
    C2[Client 2] -->|request| SRV
    C3[Client 3] -->|request| SRV
    SRV -->|response| C1
    SRV -->|response| C2
    SRV -->|response| C3
  end
  subgraph P2P[Peer-to-Peer]
    direction TB
    P1[Peer 1] <--> P2[Peer 2]
    P1 <--> P3[Peer 3]
    P2 <--> P3
    P1 <--> P4[Peer 4]
    P2 <--> P4
    P3 <--> P4
  end

OCR Exam Tip: If asked to compare client-server and peer-to-peer networks, give at least two advantages and two disadvantages of each. Always relate your answer to the context of the question.

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Worked Example

Question: A small business with 5 employees wants to set up a network to share files and a printer. Would you recommend a client-server or peer-to-peer network? Explain your answer. [4 marks]

Model Answer: A peer-to-peer network would be suitable for this scenario because:

• With only 5 employees, the network is small enough that centralised management is not essential.
• A P2P network has a lower cost because no dedicated server hardware is needed.
• It is easy to set up without specialist IT staff.
• However, if the business grows significantly, it may need to upgrade to a client-server network for better security and centralised management. [4 marks]

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Summary

• Client-server networks use a central server to manage resources, provide security, and handle backups (OCR J277 1.3.1).
• Peer-to-peer networks have no central server; all devices are equal and share resources directly.
• Client-server is better for larger organisations; peer-to-peer is simpler and cheaper for small networks.
• Each model has trade-offs in terms of cost, security, management, and scalability.

Key Vocabulary: client, server, peer, node, centralised, decentralised, scalability, congestion.

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Worked Example: Bandwidth and Latency on a Client-Server Network