Q: What is Citrix multi-stream ICA, and how does it improve performance?

A: Citrix XenDesktop 5.5 adds the option to deliver ICA traffic over multiple streams, four of which are TCP streams with a fifth UDP stream used for audio. The separation of ICA traffic into multiple streams lets administrators apply Quality of Service (QoS) prioritizations to individual components of an ICA session. Administrators can apply priorities to session features based on business needs, such as ensuring that audio quality remains high in VoIP applications even during network congestion.

With multi-stream ICA, each ICA virtual channel is associated with a class of service in delivering a user session. The four classes of service, each of which maps to a TCP stream, are the following:

  • Very High Priority: used for real-time channels such as audio
  • High Priority: used for interactive channels such as graphics, keyboard, and mouse
  • Medium Priority: used for bulk virtual channels such as drive mapping, scanners (TWAIN), and so forth
  • Low Priority: used for background virtual channels such as printing
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