Back-to-Back User Agent

Cisco introduced the back-to-back user agent starting in version 7 of the VCS platform, which provides a simplified configuration for Lync integration. To start with, the static route is completely gone from the equation and should actually be removed as part of the upgrade process if it previously existed.

The B2BUA serves a similar role for video as the Lync Mediation Server does for audio calls, and it terminates two independent calls. The difference from a static route configuration is that the endpoints no longer relay media directly to each other. Instead, the Cisco video endpoint sends a stream to the B2BUA, and the Lync endpoint does the same on the opposite side. The B2BUA does not do any kind of media transcoding or scaling, so the two endpoints still need to support the same codec as if they were still relaying traffic directly.

Although this approach simplifies the integration, it does introduce a bottleneck in the deployment because all video between the two systems must now pass through the B2BUA. This can be an issue for calls between two internal systems that must now traverse the WAN to pass through the B2BUA.

The B2BUA also enables a feature called FindMe by Cisco, which enables the B2BUA to synchronize Lync presence with a user’s Cisco endpoint and fork calls between the systems. The idea here is that if a user receives a call on his Cisco endpoint, his Lync client will ring and be answered at either endpoint. The same is true for calls to the user’s Lync endpoint.