22.1003GPPTSUMTS Phase 1
There is a special relationship between the UTRAN and GSM access networks as it is expected that UTRANs will start as islands in a sea of GSM BSS. GSM BSS access networks will be a key element for service continuity in UMTS networks. The requirements are the following for UMTS phase 1:
1) UMTS phase 1 shall support dual system UMTS/GSM terminals. At least one Capability Class shall be standardised for mobile terminals supporting the GSM and UTRA system. It shall support monitoring of cells belonging to the two types of access networks in idle mode (cell reselection procedure) and active mode (handover preparation procedure).
2) Cell selection and paging procedures shall be designed to accommodate to the fact that networks may consist of GSM BSS cells, UTRAN cells or a combination of both.
3) For UMTS networks composed of both GSM BSS and UTRAN access networks, handover of radio access bearer services shall be supported between GSM BSS and UTRAN cells, in both directions (i.e. UTRAN to GSM BSS and GSM BSS to UTRAN). Some traffic flows may be re-negotiated, temporarily released or re-established during these handover procedures because of the different radio access bearer capabilities of the GSM BSS and UTRAN access networks.