Unlicensed Mobile Access is a wireless technology that allows a seamless transition between wireless wide-area networks (e.g. GSM, 3G, EDGE, GPRS, etc.) and wireless local area networks (e.g. Wi-Fi, Bluetooth). With UMA, you can initiate a cell calls over your carrier's GSM, for example, and the call will switch from the GSM network to your office's Wi-Fi network as soon as you walk into range. And vice-versa.
How UMA Works
UMA is, in fact, a commercial name for a generic access network.
When a handset already in communication through a wireless WAN enters the area of a wireless LAN network, it presents itself to the WAN's GAN controller as being on a different base station of the WAN and shifts to the wireless LAN network. The unlicensed LAN is presented as a part of the licensed WAN, and thus the transition is smoothly allowed. When the user moves out of the range of the unlicensed wireless LAN, the connection is roamed back to the wireless WAN.
This whole process is completely transparent to the user, with no dropped calls or interruptions in data transfer.
How Can People Benefit From UMA?People can use their mobile handsets in many places and networks but still have one single number.They can set up their wireless LANs themselves, thereby solving the problem caused by holes in the coverage of their provider's network. Roaming charges outside the mobile service provider's network are eliminated because calls can be initiated within free unlicensed wireless LANs. Mobile communication becomes more reliable and cheap, incentivizing some people to replace expensive PSTN phone services.
How Can Providers Benefit From UMA?Carriers can set up Wi-Fi hotspots in-network coverage holes instead of investing in expensive wireless WAN hardware. Congestion on GSM and other wireless WAN networks are relieved with part of the traffic toggled to unlicensed wireless LANs.Networks like Wi-Fi are better for carrying other types of media apart from voice, instead of GSM. Thus, providers can design communication packages that include more than voice. This capability is especially interesting for Internet service providers eager to expand services and reduce costs.UMA operates at the IP network layer in the protocol stack and is therefore open to many protocols in the interface layer—put simply, it is not restricted to one network, but can work on Wi-Fi, Bluetooth, etc.
Disadvantages of UMAHandsets have to be UMA-compatible. These are rare and quite expensive. This is a problem both for providers and subscribers. While UMA providers mobility, it cannot provide free or very cheap calling as SIP-based services and services like Skype. As a result, cost-cutting might not be convincing in many cases.
To use UMA, you only need a wireless network plan, a wireless LAN—your own or a public Wi-Fi hotspot—and a mobile handset that supports UMA. Some Wi-Fi and 3G phones just won't work here.