1. GCSE OCR 3 A451 Computing Client-server and peer-to-peer networks
2.1.6 Computer communications and networking 3

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

3. A client-server network
The server is a powerful computer which provides services required by any of the clients
Client computers are those which people use to log on to and use the services provided by the server
Client
Query
Response
Search
Data
Server

4. 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

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

6. A server can be part of a LAN

7. 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

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

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

10. The “handshaking” process
This is the process by which two devices initiate communication
One device sends a message to another indicating it wants to communicate
If two devices try to transmit simultaneously, both wait a random time and then try again
The “handshaking” negotiation then takes place to establish what protocol to use
Computer A: “I am ready to receive data”
Computer B: “I am ready to send data”
Computer A: “OK, send it!”

11. Types of server
Servers are often dedicated computers, meaning each one performs no other tasks beside its server tasks
However, on a multiprocessing operating system, a single computer can perform the tasks of several servers

12. 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

13. Peer-to-Peer (P2P) Networks
An alternative to a client-server network
There is no central server. Each computer holds its own applications and data
All computers have equal status

14. Advantages of a peer-to-peer 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?

15. 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

16. Peer-to-peer on a WAN
The P2P configuration can also be used for file- sharing websites
BBC iPlayer, for example, uses P2P networking
This means that with thousands of people downloading, data can be passed between computers rather than just from the server
Peer-to-peer networks are often used for the illegal distribution of copyright material such as music and films, as they are very difficult to close down

17. Cloud computing Software as a Service (SaaS)
Servers host software or services that you can access

18. Online storage Dropbox, OneDrive and Google Drive How do they work?
Are these P2P or Client-Server?

19. Worksheet 3
Test your understanding with the questions on the worksheet

20. Plenary
What are the relative advantages of client server and peer-to-peer networks?

21. 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