Client-Server and Peer-to-Peer Models

At A-Level you must understand the two fundamental network models — client-server and peer-to-peer (P2P) — and be able to compare them in terms of architecture, management, security, scalability and use-cases.

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Client-Server Model

In the client-server model, a central server provides services or resources, and clients request those services. The server is a dedicated, powerful machine that is always running; clients are the end-user devices.

    ┌────────┐
    │ Client │──────┐
    └────────┘      │
    ┌────────┐      │     ┌────────┐
    │ Client │──────┼────→│ Server │
    └────────┘      │     └────────┘
    ┌────────┐      │
    │ Client │──────┘
    └────────┘

Roles

Component	Role
Server	Stores and manages shared resources (files, databases, applications); authenticates users; enforces security policies
Client	Requests services from the server; presents data to the user

Examples

• Web: A browser (client) requests pages from a web server.
• Email: An email client connects to a mail server (SMTP/IMAP/POP3).
• File server: Users save and retrieve files from a central file server.
• Database server: Applications query a central database.

Advantages

Advantage	Explanation
Centralised management	Data, backups, security, and user accounts are managed in one place
Security	The server enforces access controls and authentication; easier to apply updates and patches centrally
Backups	Centralised data makes backup and recovery straightforward
Scalability	The server can be upgraded or additional servers added
Reliability	Professional-grade hardware with redundancy (RAID, UPS)

Disadvantages

Disadvantage	Explanation
Single point of failure	If the server fails, all clients lose access (mitigated with redundancy)
Cost	Servers and professional network infrastructure are expensive
Technical expertise	A trained administrator is needed to manage the server
Bandwidth bottleneck	All traffic flows through the server, which can become overloaded

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Peer-to-Peer (P2P) Model

In a peer-to-peer network, there is no central server. Every device (peer) is equal and can act as both a client and a server — sharing and consuming resources directly.

    ┌──────┐         ┌──────┐
    │ Peer │←───────→│ Peer │
    └──┬───┘         └───┬──┘
       │                 │
       └───────┬─────────┘
           ┌───┴──┐
           │ Peer │
           └──────┘

Characteristics

• Each device stores its own files and manages its own security.
• Resources (files, bandwidth, processing power) are shared directly between peers.
• No single point of control.

Examples