UMA is a fully standardised solution, where a standard interface into the mobile core network (currently A/Gb, but soon to be Iub) allows access to all 2G and 3G services as standard. This was originally developed to allow other types of radio interface to be used with the GSM core network. It has been deployed by BT (BT Fusion) and France Telecom (Uniq) for their dual-mode GSM/WiFi systems.
There is a standard Up interface between the UNC (the femtocell controller) and the femtocells. This operates over a secure IP tunnel for privacy and security purposes.
Unlike the Iub over IP solution, this pushes more radio management functionality down into the femtocells, which allows the solution to scale to higher capacities and not rely on low-latency transmission and processing performance within the RNC.
UMA solutions were designed with the management of large numbers of access points in mind. Therefore discovery and registration techniques have been built in to avoid the need to provision each femtocell individually.
There are some issues with this approach:
1. The Iu interface from the UNC into the core network has not yet been standardised, although this is work in progress. Currently the 2G interfaces (A and Gb) are used instead, which limit the efficiency of GPRS data services and some advanced 3G services such as Video Calling.
2. UNC products have been developed by different vendors than the traditional RNC suppliers, and thus operators need to incur additional costs and complexity of integrating a new type of equipment into their operational and management systems. However, new processes are required to sell and support femtocells regardless of vendor throughout the operational, billing and customer care and marketing departments.