Unlicenced Mobile Access (UMA) originated in January 2005, when a number of equipment vendors and mobile operators wanted to extend the operation of their existing mobile networks to use other radio technologies, such as WiFi and Bluetooth. This would extend all the services and commercial features of the existing GSM mobile phone system, such as voice calls, single number, roaming etc, across to other radio technologies. Systems were developed using this scheme such as BT Fusion and Orange Unique, which required special dual-mode GSM/WiFi phones, but offered users the possibility of lower cost calls whilst in range of a WiFi hotspot. This specification was ratified by the 3GPP standards body in April 2005 and is documented in technical specification TS43.318, which was originally baselined as part of UMTS Release 6.

A mobile operator network is commonly divided into two parts:

- The Core Network, which includes all the switches and knowledge of subscribers and their general location, billing etc.

- The Access Network, which includes all the basestations, basestation controllers, radio transmitters and transmission lines back to the central switching centres.

UMA emulates the access network and connects into the core network in exactly the same way as any other 2G access network. This allows all core network services to be used in exactly the same way, including handover between access networks. However it typically requires more complexity in the end-user device (mobile phone), which must now have two different types of radio and be able to communicate using both in order to achieve a successful handover.

Femtocells simplify this by continuing to use standard 3G handsets. Thus to the core network and the handsets, everything looks and operates the same way as before. However, the femtocell is connected via the broadband IP network to the UNC and has some additional complexity to keep this simple.

In the Release 6 version of the specification, only the 2G interface between access and core network is supported. This has little effect on the services available with the exception of:

- Video Calling

- QoS management of end-to-end IP services

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