Microsofts streaming server uses the Microsoft Media Services (MMS) protocol to transfer unicast data. MMS can be transported via User Datagram Protocol or Transmission Control Protocol. If the client Windows Media Player cannot negotiate a good connection using MMS over UDP, it will resort to MMS over TCP. If that fails, the connection can be made using HTTP over TCP, which is not as ideal for streaming as MMS over UDP, but ensures connectivity nonetheless.
Information on the MMS Streaming protocol can be found at
http://sdp.ppona.com/