Sign-in for Communicator Mobile is similar to the sign-in process for Office Communicator that was previously discussed in the section Office Communicator Sign-in and Discovery.

Communicator Mobile supports NTLM authentication, which is the default Security Support Provider (SSP) on the Windows Mobile version 6.x platform. However, Office Communicator supports both Kerberos and NTLM authentication. The Kerberos protocol is also the default SSP on the Windows platform.

Windows Mobile version 6.x users can install the Kerberos SSP, but Communicator Mobile cannot use it.

Figure 1 shows the NTLM protocol messages exchanged by Communicator Mobile and the Office Communications Server 2007 R2.

Communicator Mobile sends a SIP REGISTER message. The server responds with an NTLM authentication challenge. Communicator Mobile now knows what server it needs to authenticate against. Communicator Mobile responds to the authentication challenge with another anonymous SIP REGISTER, but this time it specifies that it wants to use NTLM. This prompts the server to generate a true NTLM challenge. Communicator Mobile responds with the credentials. The server can now verify the user and process the SIP REGISTER request.

Communicator Mobile NTLM authentication

Communicator Mobile must register with the Office Communications Server infrastructure as a unified communications (UC) endpoint. However, it must indicate that it is a mobileendpoint. RFC 3840 allows for the mobility=mobileparameter during registration. The following diagram shows the call flow required to register a mobile endpoint.

Communicator Mobile endpoint registration

Communicator Mobile clients connect to an internal server or to an Access Edge server based on the network from which the device is connecting. For cellular networks, there are three main categories:

• 3G   This network enables Data and Voice connections simultaneously. Communicator Mobile requires a DTM phone with 3G networking to support simultaneous Data and Voice connections
  
  
• 2.5G   This network enables Data and Voice connections but not simultaneously.
  
  
• 2G   Voice-only network connection type
  
  

Each mobile operating system has its own set of capabilities, which is represented in the following table. D and V represent data and voice capabilities.

Note:
The J2ME client does not allow simultaneous data and voice connections, even in the DTM environment.

Dual Transfer Mode (DTM) devices can do simultaneous voice and data connections. Most Communicator Mobile users have DTM devices.

Single Transfer Mode (STM) devices alternate voice and data connections. Upon receiving a circuit switched call, these devices lose their data channel. Although Communicator Mobile supports STM devices, the data connections are dropped and are re-established when the circuit switched call has ended if Automatically sign me inis enabled.

Communicator Mobile uses the Windows Mobile 6.0 Connection Manager API for connection management functionality. Using the API, Communicator Mobile does the following tasks and activities:

• Gives priority when connecting to cellular connections such as General Packet Radio Source (GPRS) over other connections (for example, Wi-Fi, ActiveSync)
  
  
• Provides improved sign-in availability
  
  
• Reduces the frequency of signing in to and out of the application
  
  
• Reacquires the data connection when the connection drops unexpectedly
  
  
• Changes the priority of the data connection to Low (CONNMGR_PRIORITY_USERBACKGROUND) when the application moves to the background, and to High (CONNMGR_PRIORITY_USERINTERACTIVE) when a user is interacting with the device or the application has moved to the foreground
  
  
• Show relevant errors when there is a data connection loss (for example, FLIGHT_MODE or SUSPENDED/RESUME)
  
  

The following table provides details about Connection Manager sign-in errors.