Mobile UC: the ultimate end game

Rich Watson
23 Apr 2008

Staying connected with customers, partners and co-workers is vital in today's competitive economy. Missed calls can result in lost opportunities and can weaken companywide job performance. Integrating cell phone and Wi-Fi environments, and adding the benefits of presence and instant messaging, is the holy grail. Call it mobile unified communications (UC).

Mobile UC makes it possible for a smartphone to seamlessly roam between cellular and corporate Wi-Fi worlds, and support unified communications tools such as e-mail, presence, IM and contacts, and PBX desk-phone functions such as extension dialing, call forwarding and call transfer.

Mobile UC phones behave like a desk phone, which means users carry just one device and can be reached using a single business telephone number. Mobile UC users are more productive because they can be reached regardless of where they are, such as roaming or sitting at their desk with a phone and PC at arm's reach.

How mobile UC works

A total mobile UC solution consists of a server, installed on the corporate LAN, and a client installed on a smartphone. When a mobile UC user is in the office and in range of Wi-Fi, the handset client associates with the WLAN. The client conforms to the network security requirements and registers with the configured server after successful authentication and authorization. Once connected, phone calls may be made from, or received by, the client over the Wi-Fi network using Session Initiation Protocol (SIP) configured to the local hosting PBX.

Calls made from the mobile handset behave as a PBX desktop extension. They support standard PBX features and display the business PBX caller ID for calls to local or public switched telephone network, or PSTN, phone numbers.

When the user leaves the building the handset client utilizes standard cellular (GSM or CDMA) networks to register with the corporate mobile UC server. Support of capabilities such as presence, visual voice mail and secure IM is achieved without any extended service provider network enhancements. Voice calls are placed and received using the cellular voice bearer channel.

In this manner, there are no dependencies on the carrier's network; the mobile UC client appears as a normal cell phone to the carrier. But, as with Wi-Fi mode, now the client can behave like a PBX desktop phone, supporting extension dialing, call transfer, conferencing and other PBX features. And it offers the full range of UC tools available, just as when in the office and in Wi-Fi mode.

Roaming between Wi-Fi and cellular networks

Roaming between Wi-Fi and cellular networks is managed collaboratively between the mobile UC server and client, with constant monitoring that validates the robustness of the link in order to ensure call reliability and high voice quality. When call quality metrics are not met -- indicating an unreliable connection -- the call session is reestablished on the alternate network.

Before the Wi-Fi leg of the call has been terminated, the client receives the inbound cellular call and switches to the cellular audio stream without user intervention. In scenarios where loss of the Wi-Fi network is abrupt or catastrophic, the appliance will automatically invoke a process to reconnect the handset via the cellular network.

Where possible, a Wi-Fi connection is preferred because of propensity for better voice quality and a lower media cost.

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