In the first of our “A Peek Inside” articles, let’s take an easy one. When using a client makes a connection to a PowerPivot workbook that is stored inside SharePoint, how do you suppose the connection is made? If this was a regular SQL Server Analysis Services database then there are two options: either a TCP/IP connection (typically at port 2383; although the default port number changes from version to version) or a http connection. For PowerPivot we use http connections exclusively. All communication between the client and the front end web server (in SharePoint terms, it is called a WFE for Web Front-End) is done using a http connection.
The PowerPivot component that accept an in-bound connection is called the PWS, for PowerPivot Web Service. The PWS is a WCF web service that is invoked in the context of the web application for where the workbook is stored. The context includes not only the URL but also the http port and all of the other characteristics that IIS and SharePoint have setup for the web application. As the PWS is logically based on the SSAS data pump message flow (for all of you SSAS geeks out there), it does not use normal WCF remote procedure calls, instead it looks at the raw stream directly and interprets it as an old fashion SOAP call from the client libraries to the PWS.
Thus, unsurprisingly, if you were to look at the http traffic between the client and the PWS with a network monitor, you would see that the message flow is extremely like the messages that SSAS sends and receives.
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