1. Objectives
Explain the role of computers in client-server and peer-to-peer networks
Explain the advantages and disadvantages of client- server and peer-to-peer networks

2. The client-server model
The server is a powerful computer which provides services or resources required by any of the clients
A client is a computer which requests the services or resources provided by the server
Client
Query
Response
Search
Data
Server

3. Servers on LANs and WANs
One or more servers may be part of a local area network
A server may also be part of a wide area network
Google has massive servers in several different countries

4. A Google server room in Council Bluffs, Iowa
Photo: Google/Connie Zhou
See more images of Google data centres

5. A school client-server setup
File
Server
Print
Server
Mail
Server
Web
Server
Database
Server

6. Serving all your needs
In a school network, there may be dozens or even hundreds of clients and several servers
A file server holds all the data files and databases and manages backups
A print server may organise printing on different printers
An server may receive s, detect and block spam, distribute s to users
A web server may host the school’s external website

7. Role of the client The client sends requests to the server
Waits for a reply
Receives the reply

8. Role of the server The server waits for requests from a client
Acknowledges the request
The server may need to pass the request (e.g. for a web page) to another server – in which case, it becomes the “client”
The requested data is sent back to the client

9. Client-server networking
Features of a client-server network include:
A central server is used to manage security
Some files are held on the central server
Some processing tasks are performed by the server
Clients issue requests to the server for services such as , file storage, backup and printing
Suitable for many different types of organisation, small and large
Can require specialist IT staff to administer the network

10. Advantages of client-server networking
All data can be backed up centrally rather than on each individual computer
Security is better because data is held in one location rather than all over the organisation
Users can log in from any computer on the network and access their data

11. Peer-to-peer (P2P) structure
A peer-to-peer network has no central server

12. Peer-to-peer networking
Features of a peer-to-peer network include:
Suitable for a small companies with fewer computers
No central server controls files or security
All computers can easily see files on all other computers
All computers can communicate with each other without going through a server
If a computer is switched off, data cannot be retrieved

13. Advantages of a P2P network
Easier to set up – computers can simply be cabled together
No special software is required to run the network
Individual computers can share a printer, router, modem and other hardware
Users can communicate directly with each other and share each others’ files
Where would you use a peer-to-peer network?
What are the disadvantages?

14. Drawbacks of a peer-to-peer network
Viruses and malware are easily transferred over this type of network
Data recovery and backup is not done centrally, so each computer has to have its own backup system
Files are not centrally organised, but stored on individual computers and may be hard to locate if the computer’s owner does not have a logical filing and naming system

15. Client server vs Peer-to-Peer
A central backing store is available to all computers
Storage facilities are distributed across all computers
Security is controlled by the central computer
Security is not centrally controlled
Backup is done centrally on the server
Backup must be done separately for each computer
All users are reliant on the central server
No central server
Can support hundreds or even thousands of users and grow with an organisation
Easy to set up but most suited to homes and small businesses