Today, we'll briefly cover Unlicensed Mobile Access technology as we prepare to compare UMA with an IP-Multimedia Subsystem architecture. Like IMS, UMA technology has its origins with the wireless (cellular/mobile) community and the technology's specifications have been developed with collaboration from the Third Generation Partnership Project (3GPP) and other standards bodies.

UMA's main objective is to allow a common way for dual-mode wireless handsets to move (roam) between "unlicensed" wireless network connections like those provided in a Wi-Fi (IEEE 802.11) or a Bluetooth transmission, and a GSM or General Packet Radio Service (GPRS) network connection. Unlike the multi-part IMS architecture, the UMA architecture is less complicated, with the principle component called the UMA Network Controller (UNC). The architecture also includes security components like AAA and security gateways.

The UNC typically sits inside the “unlicensed” network zone and sits between the Unlicensed Mobile Access Network (UMAN) and a carrier’s “licensed” mobile network. The UMS knows where to route calls as they come and go through a wireless access point; it connects to wireless access points (like an 802.11 router) via the IP network core on the “unlicensed” side and to the core mobile network on the other side. It is responsible for monitoring and (in cooperation with the AAA server) for users' authentication as the move in and out of the UMAN range, and it is designed to complete a transparent hand-off between the networks. The UNC is also responsible for storing the user’s location so the mobile network “knows” where to route calls for a dual mode handset that is in range of the UMAN. Specifically, the UNC "tunnels" GSM/GPRS connections over a Bluetooth or Wi-Fi connection.

Next time, we'll discuss how IMS and UMA can and should work together, and provide comments about "fixed-mobile" convergence.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Larry Hettick is a principal analyst at Current Analysis.