Client-server and peer to peer models

what is a client-server model?

• client accesses data, services and files from the server

• clients can have some of their own files and resources

• client initiates communication to the server and issues requests

• server waits for requests from clients

• servers can be file, print, mail, web and database

more features of client-server model

central server manages security and some processing tasks

files held on central server

suitable for many small and large organisations

can require specialist IT staff to administrate

can be expensive to set up and manage

centralised and automated backup

server manages access rights which is more secure because no unauthorised access to other users files

what things happen in client side processing?

• data is processsed before being sent to server

• web page does not communicate with server at this point

• initial data validation in javascript, executed by browser

• manipulation of user interface elements

• applying website styles in css

what are the advantages of client side processing in javascript?

• reduces unnecessary load on the server, saves processing resources

• reduces the amount of web traffic so no communication with server required

• allows interactivity and quick response to user actions

• data not intercepted on way to server

disadvantages of client side processing?

• not all browsers support all scripts

• scripts can run slow if user machine is slow

• scripts can be processed differently depending on browser

what things happen in server-side processing?

• further validation

• queries and updates server database or permanent storage

• encodes data into readable HTML

• performs complex calculations

• structure web applications

• process user input

what are the advantages of server-side processing

• good when client does not have capability to successfully process a request (eg not having the data for it)

• keeps organisation data secure as sensitive data is needed to process request

• good when the client isn’t allowed to know how data is processed (it’s a company secret)

• further validation is good because the user could have circumvented javascript so extra validation makes sure data is accurate and secure

what is a peer to peer model?

has no central server to control file/security so easy to maintain

suitable for small company/home network

files are stored on individual computers, which are all connected to each other

all computers can access the other computers’ files and share resources

computers can communicate without going through server so cheap to set up

if computer switched off, cannot retrieve data from it

can be used for sharing music and livestreams

what is an api?

• application programming interface

• set of protocols that govern how two applications interact

• sets out the format of requests and responses between client and server

• enables one application to make use of another’s services

• can be used for building software applications

• api requests are processed by client and responded to by relevant server

what are thick and thin clients?

• thickness of a client refers to how much processing and storage it does compared to the server

• server does more processing → thin client

• server does less processing → thick client

advantages of thin clients

• easy to set up, maintain and add clients to network because they’re so basic

• software and updates can be installed on server and automatically distributed to each client terminal

• more secure because data kept centrally

disadvantages of thin clients

• reliant on server, so if server goes down clients lose functionality

• requires very powerful and expensive and reliable server

• server needs more bandwidth due to high demand

• maintaining network connections for portable devices consumes more battery than local processing

advantages of thick clients?

• clients are more robust and reliable due to high processing power

• can operate without continuous connection to server

• good for powerful software

disadvantages of thick clients?

• thick clients are more expensive with higher spec because higher processing power

• software has to be individually installed on each client computer

• more network administration time

• data integrity issues in distributed systems