by Wes Joyner

Created on: September 14, 2008

Your computer has a busy schedule. In order to facilitate better communication with the Internet, it employs user agents to handle the task of effectively working with various protocols. Once these agents have transacted business with the network at large, they tell your applications how to present the information to you.

User agents are an intermediary between servers and clients. In general cyberspace terms, a server is a computer storing online information and a client is a device requesting that information. As user agents are working on behalf of the client side of this relationship, you may hear it referred to as a client program. These programs are designed to interact with a specific protocol or set of protocols that deliver network content and services. Your computer has user agents to negotiate with Hyper-Text Transfer Protocol (World Wide Web), Simple Mail Transfer Protocol and Post Office Protocol (e-mail), and File Transfer Protocol, just to name a few!

To illustrate, imagine talking to a crowd of ten million people who all speak different languages. In this crowd, there are ten people who are each fluent in your language, as well as one million others. Would it be easier to directly address the entire assembly in your own language or speak to the group of ten, who are then able to communicate your message to everyone? Along these lines, Internet developers create their server applications with user agents in mind, as these agents provide a streamlined way to communicate with every device accessing the server. Your user agent is a sort of translator that can speak the language of its associated protocol as well as your computer's specific dialect.

This communications model can be used to govern a wide range of server-client interactions. On the World Wide Web, user agents represent browsers like yours as well as spiders and web crawlers, which are the tools search engines use to scour the Internet for content to catalog. The servers on the web can choose which agents have access to specific content, and may choose to talk to your browser while excluding spiders by way of the Robot Exclusion Standard.

Furthermore, many server applications, particularly web pages, use bits of code to determine which agent is requesting data, and content may be dynamically adjusted to present minor variations or entirely different experiences based on your user agent. This "sniffing" allows programmers to deliver a custom experience that differentiates between a visitor using Microsoft Internet Explorer and another using Mozilla Firefox; it could even tell you if your browser version is too obsolete to effectively view the content.

As you navigate around the World Wide Web, check your e-mail, download music, or even use your cell phone, your user agents are hard at work to ensure that the Internet speaks to you in a way you can understand!

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