 error likelihood information gener- ated by the demodulation function to increase the efficiency of the decoding operation. The channel decoding function, located in both the UE and UTRAN, complements the channel coding function. 3.4.5.10 Initial Random Access This function, located in the UTRAN, detects initial MS access attempts and responds accordingly. Handling this initial access may incorporate procedures to resolve collid- ing events. Successful attempts will obtain the right to resource allocation request. The UMTS Development Platform 3.4.5.11 NAS Core Network Distribution Functions Non-Access Stratum Messages (NAS) messages in the RRC protocol have transparent transfer within the access stratum through a direct transfer procedure. A UE/SRNC dis- tribution function handles a CN domain indicator, service descriptor, and flow ID being part of the AS message to direct messages to the corresponding NAS entity, i.e. the ap- propriate mobility management instance in the UE domain and the corresponding CN domain. In the downlink the SRNC provides the UE with the necessary information on the origi- nating CN domain for the individual NAS message. In the uplink, the UE distribution function inserts the appropriate CN domain values, domain indicator, service descriptor, and flow ID IEs in the AS message. The SRNC evaluates the CN domain indicator, service descriptor, and flow ID contained in the AS message and distributes the NAS message to the corresponding RANAP instance for transfer over the Iu interface. 3.4.5.12 Timing Advance in TDD This function aligns uplink radio signals from the UE to the UTRAN. It is based on uplink burst timing measurements performed by the Node B L1, and on timing advance commands sent downlink to the UE. 3.4.5.13 NAS Service Specific Function A UE or SRNC service specific function provides a SAP for particular services (e.g. priority levels). In the downlink direction, the SRNC may base the routing on this SAP. MOBILITY MANAGEMENT 3.5.1 Signalling Connection The UE may or may not ha