The protocol documentation for the Remote Desktop Protocol (RDP) is published on the MSDN website:

The table below lists the various documentation available specific to RDP with recent changes:
Remote Desktop Protocol Documentation Date Change Version
[MS-RDPADRV]: Remote Desktop Protocol: Audio Level and Drive Letter Persistence Virtual Channel Extension 1/31/2013 1.1
[MS-RDPBCGR]: Remote Desktop Protocol: Basic Connectivity and Graphics Remoting 1/31/2013 34
[MS-RDPCR2]: Remote Desktop Protocol: Composited Remoting V2 12/16/2011 15
[MS-RDPEA]: Remote Desktop Protocol: Audio Output Virtual Channel Extension 7/12/2012 13
[MS-RDPEAI]: Remote Desktop Protocol: Audio Input Redirection Virtual Channel Extension 7/12/2012 8
[MS-RDPECLIP]: Remote Desktop Protocol: Clipboard Virtual Channel Extension 12/16/2011 9
[MS-RDPEDC]: Remote Desktop Protocol: Desktop Composition Virtual Channel Extension 12/16/2011 7
[MS-RDPEDYC]: Remote Desktop Protocol: Dynamic Channel Virtual Channel Extension 7/12/2012 11
[MS-RDPEECO]: Remote Desktop Protocol: Virtual Channel Echo Extension 12/16/2011 1
[MS-RDPEFS]: Remote Desktop Protocol: File System Virtual Channel Extension 10/25/2012 20
[MS-RDPEGDI]: Remote Desktop Protocol: Graphics Device Interface (GDI) Acceleration Extensions 1/31/2013 26.1
[MS-RDPEGFX]: Remote Desktop Protocol: Graphics Pipeline Extension 1/31/2013 4
[MS-RDPEGT]: Remote Desktop Protocol: Geometry Tracking Virtual Channel Protocol Extension 10/25/2012 2
[MS-RDPEI]: Remote Desktop Protocol: Input Virtual Channel Extension 10/25/2012 3
[MS-RDPELE]: Remote Desktop Protocol: Licensing Extension 10/25/2012 11.2
[MS-RDPEMC]: Remote Desktop Protocol: Multiparty Virtual Channel Extension 12/16/2011 9
[MS-RDPEMT]: Remote Desktop Protocol: Multitransport Extension 1/31/2013 4
[MS-RDPEPC]: Remote Desktop Protocol: Print Virtual Channel Extension 12/16/2011 5
[MS-RDPEPNP]: Remote Desktop Protocol: Plug and Play Devices Virtual Channel Extension 10/25/2012 13
[MS-RDPEPS]: Remote Desktop Protocol: Session Selection Extension 12/16/2011 10
[MS-RDPERP]: Remote Desktop Protocol: Remote Programs Virtual Channel Extension 12/16/2011 15
[MS-RDPESC]: Remote Desktop Protocol: Smart Card Virtual Channel Extension 12/16/2011 9
[MS-RDPESP]: Remote Desktop Protocol: Serial and Parallel Port Virtual Channel Extension 12/16/2011 8
[MS-RDPEUDP]: Remote Desktop Protocol: UDP Transport Extension 1/31/2013 4
[MS-RDPEUSB]: Remote Desktop Protocol: USB Devices Virtual Channel Extension 10/25/2012 12
[MS-RDPEV]: Remote Desktop Protocol: Video Redirection Virtual Channel Extension 1/31/2013 10.1
[MS-RDPEVOR]: Remote Desktop Protocol: Video Optimized Remoting Virtual Channel Extension 1/31/2013 4
[MS-RDPEXPS]: Remote Desktop Protocol: XML Paper Specification (XPS) Print Virtual Channel Extension 12/16/2011 9
[MS-RDPNSC]: Remote Desktop Protocol: NSCodec Extension 10/25/2012 7
[MS-RDPRFX]: Remote Desktop Protocol: RemoteFX Codec Extension 1/31/2013 15
[MS-RDSOD]: Remote Desktop Services Protocols Overview 10/25/2012 2
[MS-RDWR]: Remote Desktop Workspace Runtime Protocol 12/16/2011 1
[MS-TSGU]: Terminal Services Gateway Server Protocol 7/12/2012 30.1
[MS-TSSO]: Terminal Services System Overview 6/17/2011 6.2
[MS-TSTS]: Terminal Services Terminal Server Runtime Interface Protocol 12/16/2011 18
[MS-TSWP]: Terminal Services Workspace Provisioning Protocol 10/25/2012 9.1


Questions regarding protocol documentation are handled by the Open Protocols Documentation support team which can be reached at dochelp@microsoft.com  There is also a public forum: http://social.msdn.microsoft.com/Forums/en/os_windowsprotocols/threads