White Paper V600
Access Network and other radio systems such as GSM/GPRS. As a principle, the requirements on service continuity characteristics should be according to the target network on which the service is maintained.
Service continuity
Service continuity should support the following scenarios:
•Continuity of active circuit switched services when moving within UMTS Radio Access Net- work, within GSM/GPRS and between UMTS Radio Access Network and GSM/GPRS cover- age areas.
•Continuity of active and packet switched ses- sions when moving within UMTS Radio Access Network, within GSM/GPRS and between UMTS Radio Access Network and GSM/GPRS coverage areas.
General operational considerations
Mechanisms defined to support service continuity between different radio systems or radio access modes should effectively cope with a number of coverage scenarios:
•Limited coverage in a “sea” of coverage pro- vided by another radio system or radio access mode.
•Selective operation at a geographical boundary, with extensive UMTS Radio Access Network coverage on one side, and extensive coverage from another radio system on the other side.
•Geographically
Performance requirements
Temporary degradation of service caused by handover
During
The duration of the discontinuity experienced by packet switched and circuit switched real time services should be shorter than that in the hando- ver of voice calls over GSM/GPRS.
Requirements on multiple bearer services handover from UMTS Radio Access Network to GSM/
GPRS
Consideration must be given to services that may involve multiple bearer services (and simultaneous sessions). The mapping between UMTS Radio Access Network bearer services and GSM/GPRS bearer services depends on many factors such as data rate, delay constraints, error rate etc. In the event that certain UMTS Radio Access Network bearer services cannot be handed over to GSM/ GPRS, the handover of some of the bearers to maintain the service should not be precluded.
In the case where a user equipped with a dual mode terminal is in UMTS Radio Access Network 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 GSM/GPRS should be candidates for handover.
If there are still multiple PDP contexts as “handover candidates”, then the operator should choose which PDP is maintained. When roaming, the serving network should make this decision. The operator may choose to either:
•Drop all of the PDP contexts.
•Choose one based upon criteria such as dura- tion, amount of traffic transferred, etc.
17 | August 2005 |