6 Requirements for Handover from UTRAN to GERAN
22.1293GPPHandover requirements between UTRAN and GERAN or other radio systemsRelease 17Service aspectsTS
6.1 Operational Requirements
6.1.2 GERAN bands
The standard shall support handover to any combination of GERAN bands supported by the specifications.
6.2 Performance Requirements
The following service principles apply to performance requirements:
– When the UE performs handover to GERAN then the service requirements of GERAN that relate to handover between different cells in different location areas is taken as the benchmark. It is not the intention to set more stringent service requirements for UTRAN to GERAN handover than are already commonly accepted for handover within GERAN.
6.2.1 Detection Time of Potential GERAN Handover Candidates
Means shall be defined which allow the UE to achieve as good detection time performance as the GERAN benchmark: i.e. to behave in such a way as to detect potential handover candidates as quickly as a mobile performing an intra GERAN handover is required to do so.
6.2.2 Number of GERAN handover candidates to detect
Means shall be available which allow UE to detect an equal number of GERAN handover candidates relative to the GERAN benchmark, i.e. to behave in such a way as to detect as many potential handover candidates as a mobile performing an intra GERAN handover is required to do so.
6.2.3 Probability of Connection Loss
The service requirement is that it should be possible to hand over to GERAN from UTRAN with a probability of connection loss that fulfils the corresponding service requirement for intra GERAN handover.
6.3 Specific Requirements for Individual Services from UTRAN to GERAN
6.3.1 Speech
Handover of a CS Speech teleservice (TS11) from UTRAN to GERANis required. This requirement also applies to emergency calls (TS12):
– Any call based on the default UTRAN speech codec (AMR) shall be mapped to the FR GSM speech codec. In the case the terminal and the GERAN network support AMR and /or EFR and/or HR, it shall be the operators choice to define the appropriate mapping.
Means shall be defined which make it possible to limit any temporary degradation on handover so it meets the performance specified by GERAN service requirements for speech handover.
6.3.2 Short Message Service
There are no requirements related to handover for short message service.
6.3.3 Cell Broadcast
There are no requirements related to handover for cell broadcast.
6.3.4 USSD
The technical specifications shall provide means to ensure that any handover that occurs during a USSD interaction need no more affect the service than intra-GERAN handover.
6.3.5 Facsimile
It is not required that a facsimile transmission that is active between UE and network at the time of handover from UTRAN to GERAN completes successfully.
6.3.6 Data Bearer Services
6.3.6.1 Circuit Switched Data
Specifications shall be defined to permit the possibility of handover of a UTRAN data bearer service to GERAN
Means shall be defined which make it possible to limit any temporary degradation on handover so it meets the performance specified by GERAN service requirements for data bearer service handover.
6.3.6.2 Packet Switched Data
It is required to handover a user PS context between GERAN and UTRAN. Independently of the used air interface, the user shall stay connected to an external network (internet, intranet).
6.3.7 Supplementary Services
Control and use of Supplementary Services should not be effected by a handover to GERAN.
6.4 Requirements on multiple bearer services handover from UTRAN to GERAN
Consideration must be given to services that may involve multiple bearer services. The mapping between UTRAN bearer services and GERAN bearer services will depend upon many factors such as data rate, delay constraints, error rate etc. In the event certain UTRAN bearer services cannot be handed over to GERAN, the handover of some of the bearers to maintain the service should not be precluded.
In the case where user equipped with a dual mode terminal is in UTRAN coverage and has multiple PDP contexts activated (for instance to support multimedia) then it is preferable to handover one PDP context, rather than dropping all of them.
As a first priority only the PDP contexts which have an associated QoS that can be supported by the GERAN should be candidates for handover.
If there are still multiple PDP contexts as "handover candidates" then it shall be an operator choice which PDP context will be maintained. When roaming this decision shall be taken by the serving network. The operator may choose to either;
a) Drop all of the PDP contexts.
b) Choose one based upon criteria such as duration, amount of traffic transferred, etc.
In case of UTRAN to GERAN handover of a Multicall only one call can be handed over.