atum USIM HN USIM-MT MT SN SN HN Serving Stratum USIM MT MT SN Transport Stratum Access Stratum MT AN AN SN MT/ME Access Serving Network Network Network Domain Domain Domain Figure 3.16 UMTS Architecture functional flow. Because of the incorporation of the remote party in Figure 3.16, the home (through the application stratum, the serving and transport strata are extended all the way to the re- mote party line in the representation. Hence, two diversion paths reflect the flows ex- changed between serving and home domains on one side and between serving and tran- sit on the other side. Starting the first layer the stratum levels are defined in Table 3.6. The UMTS Development Platform Table 3.6 Definition of the Strata Layers Stratum levels Transport stratum Supports the transport of user data and network control signalling from other strata through UMTS. It includes: considerations of the physical transmission formats used for trans- mission; mechanisms for error correction and recovery; mechanisms to encrypt data over the radio interface and in the infrastructure part if required; mechanisms for adaptation of data to use the supported physical format (if required); and mechanisms to transcode data to make efficient use of, e.g. the radio interface (if required); may include resource allocation and routing local to the different interfaces (if required); the access stratum, which is specific to UMTS, as the part of the transport stratum. Access stratum Consists of User Equipment (UE) and infrastructure parts, as well as access-technique specific protocols between these parts (i.e. spe- cific physical media formats between the UE and the infrastructure used to carry information). It provides services related to the transmission of data over the radio interface and the management of the radio interface to the other parts of UMTS. The access stratum includes the following protocols: Mobile Termination - Access Network (MT-AN) protocol support- ing transfer of detailed radio-related information to coordinate the use o