1.3.3 Static Virtual Channels
Static Virtual Channels allow lossless communication between client and server components over the main RDP data connection. Virtual channel data is application-specific and opaque to RDP. A maximum of 31 static virtual channels can be created at connection time.
The list of desired virtual channels is requested and confirmed during the Basic Settings Exchange phase of the connection sequence (as specified in section 22.214.171.124) and the endpoints are joined during the Channel Connection phase (as specified in section 126.96.36.199). Once joined, the client and server endpoints do not exchange data until the connection sequence has completed.
Static Virtual Channel data is broken up into chunks before being transmitted. The maximum size of an individual chunk is determined by the settings exchanged in the Virtual Channel Capability Set described in section 188.8.131.52.10 (the chunk size does not include RDP headers). Each virtual channel acts as an independent data stream. The client and server examine the data received on each virtual channel and route the data stream to the appropriate endpoint for further processing. A particular client or server implementation can decide whether to pass on individual chunks of data as they are received, or to assemble the separate chunks of data into a complete block before passing it on to the endpoint.