Client-server Technologies

Paradigm where providers of resources are designated as servers and resource requesters are designated as clients

Refers to any operations carried out on the ‘client’ side of relationship. Almost always some processing carried out by client

Typical example of client-side processing Formats a web page according to the HTML tags and CSS styling sent to it by server HTML pages can include scripts, can carry out tasks such as validating form data and creating dynamic page features Scripts interpreted by web browser

Offloads processing to client, reducing load on server and reduces communications bandwidth

security risk as malicious content can be easily distributed as code that creates a stunning slide show

Set of functions and protocols that clients use

Set of web services or web resources to enable programmers to build web applications

Multiple can be used to create combined web applications called mashups

Operations carried out on server

Web browser sends a HTTP request Sends and retrieves data to/from database via a server-side script Server-side script provides a HTTP response, sending web page to web browser

• more control over environment where scripts are executed. Developers know which version of interpreter will be used • scripts hidden on server, helps protect intellectual copyright & prevents tampering • servers can be optimised to cope with heavy processing demands

Provides persistent full duplex connection between client & server. Means both client and server can use connection to start sending data any time

Data can be pushed from server without having to be initiated by HTTP request from client. Reduces latency as once connection is made messages are automatically received without need for security checks

As messages, each consist of one or more frames that are reconstructed when received

Text frames Binary frames e.g. image data ‘Ping/pong’ frames (used to check connection) Control frames e.g. to close connection