When you open an FPSE-extended Web site (or a SharePoint site) for live editing, SharePoint Designer internally has to perform a lot of operations, such as discovering the remote-authoring mechanism supported by the Web site, opening the site, listing the files and folders of the Web site, and determining the properties associated with the files. Even more such background operations need to be performed to implement other SharePoint Designer features, such as saving Web pages, publishing content, etc.
SharePoint Designer accomplishes these operations by using an HTTP-based protocol called FrontPage Remote Procedure Call (RPC). This protocol is the key component enabled for use on a Web site when you extend it with FPSE (or set up a SharePoint site).
The remote-authoring operations are performed in the FrontPage RPC protocol by using Web methods. A Web method, simply put, is a function implemented by the remote-authoring mechanism (FPSE or SharePoint) that performs a specific operation. For example, the Open Service Web method offered by FPSE provides the necessary metadata information about a Web site that SharePoint Designer can later use to open the Web site.
To understand FrontPage RPC better, I take you through the operations performed when you open an FPSE-extended Web site in SharePoint Designer and then discuss the Web methods involved:
Open Fiddler and then choose File