According to Wikipedia a user agent is the client application used with a particular network protocol; the phrase is most commonly used in reference to those which access the World Wide Web. Other systems, such as Session Initiation Protocol (SIP), use the term user agent to refer to both end points of a phone call, server and client.
Web user agents range from web browsers and e-mail clients to search engine crawlers ("spiders"), as well as mobile phones, screen readersand braille browsers used by people with disabilities. When Internet users visit a web site, a text string is generally sent to identify the user agent to the server. This forms part of the HTTP request, prefixed with User-Agent: (case does not matter) and typically includes information such as the application name, version, host operating system, and language.
To put it simple in a mobile phone the user agent (UA) you are using to browse the Internet is your mobile phone browser. In most cases this client is user to view received MMS also.
In the next post we will discuss about how can we lean which user agent we are using and what does this mean.
If you have any comments please feel welcome to post them.
