An update is available for Microsoft Lync Server 2010 users to be able to enable the RTAudio narrowband without using the Call Admission Control (CAC) session. The RTAudio narrowband exists between Lync 2010 clients and the Lync Server 2010 Mediation servers across a wide area network (WAN).
Additionally, if the client detects a round-trip delay of more than 25ms, it automatically flips to a low-bandwidth codec (for example, Siren instead of G.722 for the conference audio). This is done to be more considerate on WAN links to customers who have not yet deployed CAC.
To enable this feature, install the following cumulative update:
2514982 Description of the cumulative update for Lync 2010: November 2011
For more information about Call Admission Control, visit the following Microsoft websites: