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Bandwidth Allocation For Terminal Server Connections Over RDP

Wednesday, 11 April 2007 by Michel Roth

This little article from the Microsoft Terminal Services Team is about a new possibility of Vista and Longhorn RDP (Terminal Services) to manage the bandwidth within the RDP protocol. This is a perfect example of how Microsoft is developing the RDP protocol to be a good fit for more and more customers. One of the features that for example is in ICA but not in RDP today - that many customers really like- in the ability to set limits per virtual channel or, more importantly, per session. Al though the Microsoft tweak for the RDP bandwidth allocation isn't as advanced, it's a clear example of how Microsoft is moving forward with Terminal Server.

"Over a Terminal Server RDP connection, there are multiple applications (for example video, clipboard, printer output etc) that send data over the connection from server to client. On a low bandwidth connection these applications compete for available bandwidth. As a result, important graphics data, such as the location of a window the user moves on the desktop, has to compete with data transmitted in the background, like a print job or a file copy. This problem manifests itself most severely when printing a large document over a low bandwidth connection. The printer data competes for available bandwidth with the video rendering, thus deteriorating the graphics rendering significantly.

In Vista (and Longhorn Server) we fix this by introducing a simple scheme wherein a fixed percentage of bandwidth is allocated to video, and the rest goes to virtual channel traffic (this means all kind of redirections). By default this allocation is 70% for Video and 30% for virtual channel data, meaning when bandwidth usage is under pressure video data is guaranteed to get 70% of the available bandwidth."

Read it here.