The Background Intelligent Transfer Service (BITS) has two role services: the Compact Server and the IIS Server Extension. The Compact Server is a stand-alone HTTP or HTTPS file server, whereas the IIS Server Extension is an Internet Information Services (IIS) plug-in that requires a server running IIS.
IIS Server Extension
The BITS IIS Server Extension lets you configure a server that is running IIS to allow BITS clients to perform background, resumable file uploads to IIS virtual directories. On completion of a file upload, the BITS Server can notify a Web application of the newly uploaded file. This allows the application to process the uploaded file. The Web application can then optionally reply to the client responsible for the upload.
The BITS Compact Server is a stand-alone HTTP or HTTPS file server, which allows applications to host files for BITS clients to download, and allows the asynchronous transfer of a limited number of large files between computers.