Protocol Listeners
Protocol listeners receive protocol-specific requests, send them to IIS for processing, and then return responses to requestors. For example, when a client browser requests a Web page from the Internet, the HTTP listener, HTTP.sys, picks up the request and sends it to IIS for processing. Once IIS processes the request, HTTP.sys returns a response to the client browser.
出处：http://cnblogs.com/daishuguang
