f radio resources between the MT and AN. Access Network - Serving Network (AN-SN) protocol supporting the access from the SN to the resources provided by the AN. It is independent of the specific radio structure of the AN. Serving stratum Consists of protocols and functions to route and transmit user or network generated data/information from source to destination. The source and destination may be within the same or different networks. It contains functions related to telecommunication services, and includes: USIM - Mobile Termination (USIM-MT) protocol supporting ac- cess to subscriber-specific information to allow functions in the user equipment domain. Mobile Termination - Serving Network (MT-SN) protocol support- ing access from the MT to the services provided by the serving network domain. Terminal Equipment - Mobile Termination (TE-MT) protocol sup- porting exchange of control information between the TE and the Home stratum Consists of protocols and functions related to the handling and stor- age of subscription data and possibly home network specific ser- vices. It also includes functions to allow domains other than the home network domain to act on behalf of the home network. It contains functions related to subscription data management and customer care, as well as billing and charging, mobility manage- ment and authentication. The home stratum includes the following protocols: The UMTS Network and Radio Access Technology USIM - Home Network (USIM-HN) protocol supporting co- ordination of subscriber-specific information between USIM & HN. USIM - Mobile Termination (USIM-MT) protocol providing the MT with access to user specific data and resources necessary to perform actions on behalf of the home network. Mobile Termination - Serving Network (MT-SN) protocol support- ing user specific data exchanges between the MT and the SN. Serving Network - Home Network (SN-HN) protocol providing the SN with access to HN data and resources necessary to perform its actions on behalf of the HN, e.g. to support the user