Understanding the Mobility Service

To enable Lync 2010 mobile clients to communicate with Lync servers, a new service was introduced in Lync Server 2010. Mobile clients communicate over HTTPS with XML messages. A service was introduced to translate traffic and allow these clients to communicate with the Lync Server infrastructure that operates on SIP. The MCX Service is the service responsible for translating mobile communications into SIP communications that Lync Servers can understand. In Lync Server 2013, a new service is introduced, the Unified Communications Web API (UCWA); it is used to facilitate communications from all HTTPS-based clients. This service is open to developers, and is also responsible for providing Lync Web App connectivity. Lync 2013 mobile clients will connect to the UCWA service, and Lync 2010 clients will continue connecting to the MCX service for legacy compatibility.

SIP traffic is often referred to as chatty—chatty traffic can consume a lot of bandwidth and power. When a mobile client is being deployed, it is critical that this client does not decrease the increasingly precious battery life of mobile devices. By implementing an HTTPS/XML-based client, Microsoft is able to achieve the following:

• Standardize and simplify the clients across multiple platforms

• Decrease the frequency and size of traffic used when compared with SIP

• Decrease the battery drain of the mobile clients

• Increase session resiliency and session recovery time for mobile clients, which are often changing connection state frequently

The Lync Mobility Services act under a simple concept: translate mobile XML messages to SIP messages that Lync Servers can understand. This service acts much like a back-to-back user agent (B2BUA), receiving a request from a mobile device and then initiating another request over SIP and maintaining the state of the two separate connections. The Mobility Services will perform functionality such as updating presence, initiating calls, and issuing push notification requests.

The Lync UCWA and MCX services are deployed on all Front End Servers in the environment, and details on the actual messages exchanged between clients and servers will be shown in the “Putting It All Together: Protocol Flow” section.