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

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

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

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

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

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 email server may receive emails, detect and block spam, distribute emails to users A web server may host the school’s external website

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

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

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 email, file storage, backup and printing Suitable for many different types of organisation, small and large Can require specialist IT staff to administer the network

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

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

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

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?

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

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