4 General Principles governing service continuity

22.1293GPPHandover requirements between UTRAN and GERAN or other radio systemsRelease 17Service aspectsTS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.0 General Principles for service continuity

The general principles for service continuity described in this specification refer to service continuity within the UTRAN, within the GERAN and between the UTRAN and GERAN. As a principle, the requirements on service continuity characteristics should be according to the target network on which the service is maintained.

Service requirements for seamless mobility between multiple heterogeneous access systems beyond only UTRAN and GERAN are contained within TS 22.278 [2].

4.1 Service Continuity Scenarios

Service continuity shall support the following scenarios:

1. Continuity of active CS services when moving within UTRAN, within GERAN and between UTRAN and GERAN coverage areas.

2. Continuity of active GPRS sessions when moving within UTRAN, within GERAN and between UTRAN and GERAN coverage areas.

3. Continuity of active IM Services when moving within UTRAN, within GERAN and between UTRAN and GERAN coverage areas (that support those IM services).

Service continuity is not applicable for any call or session using resources specific to the source domain that cannot be maintained using resources in the target domain.

4.2 Service Continuity requirements

For all scenarios, the specifications shall cover both service continuity within the same PLMN (intra-PLMN) and between PLMNs (inter-PLMN), including the case where the PLMNs involved are operated by different network operators.

It shall be possible for a user to roam between the different parts of a shared network without requiring any user intervention. The user experience while roaming in a shared network shall be comparable to the user experience while roaming in a non-shared network.

4.2.1 Service continuity for CS

The scenario numbers in this table refer to the scenarios in section 4.1.

		To CS services
		UTRAN	GERAN
From CS services	UTRAN	Yes – Scenario 1	Yes – Scenario 1
From CS services	GERAN	Yes – Scenario 1	Yes – Scenario 1

4.2.2 Service continuity for GPRS

Service continuity of GPRS sessions (conversation, streaming, interactive and background) is required within the GERAN, within the UTRAN, and between the UTRAN and GERAN (scenario 2 in section 4.1 above).

Note: Service continuity for conversational, streaming and interactive GPRS sessions is not applicable to and from GERAN Release 4 or earlier, due to the lack of support for the conversational, streaming and interactive GPRS within GERAN Release 4 or earlier. In these cases, although the QoS required may not be available in the target, the bearer shall be maintained as long as possible. If the QoS supported by GERAN is not acceptable, the user/application may terminate the session.

4.2.3 Service continuity for IM Services

Service continuity of IM services is required within the GERAN, within the UTRAN, and between the UTRAN and GERAN (scenario 3 in section 4.1 above).

Note: Service continuity of IM Services is not applicable to and from GERAN Release 4 or earlier as the IM Services service classes are not supported by GERAN Release 4 or earlier. In these cases, although the QoS required may not be available in the target, the bearer shall be maintained as long as possible. If the QoS supported by GERAN is not acceptable, the user/application may terminate the session.

4.3 General Operational Considerations

4.3.1 Coverage environment

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 provided by another radio system or radio access mode, or vice versa;

– Selective operation at a geographical boundary, with extensive UTRAN coverage on one side and extensive coverage from another radio system on the other side;

– Geographically co-located areas of UTRAN coverage and another radio system.

However the specifications should impose no restrictions or assumptions on how an operator might deploy or operate the network in both GERAN and UTRAN.

4.3.2 Inter PLMN Handover Issues

Handovers to support service continuity between PLMNs should remain an optional feature to implement. It is envisaged that handover would take place due to changing radio conditions caused e.g. by movement of the terminal causing it to leave the coverage area of a PLMN.

The following networks may be involved with an inter-PLMN handover procedure. These concepts are illustrated in Annex A:

– The user’s home network, i.e. the operator where the user’s subscription may be found;

– The user’s visited network where the subscriber user is currently registered, i.e. the network where the subscriber user has performed the last successful update location procedure. As long as the subscriber user is roaming within the home network, home and visited network are identical;

– The user’s serving network covering the cell that serves the subscriber. After successful completion of the update location update procedure, the serving network is identical with the visited network. After an inter-PLMN handover, the visited network is different from the serving network until a location update procedure has been successfully completed (excepted the case that the subscriber returns into the visited network);

– The target network covering candidate target cell(s) for inter-PLMN handover. The target network has overlapping radio coverage with the serving network but not necessarily with the visited network.

The minimum requirements for inter-PLMN HO are:

– Continuity of an active call across the handover procedure, where this would be possible for intra-PLMN handover;

– The decision whether the handover request is accepted must be taken by the target network.

4.3.3 Charging and Network Management

Means shall be standardised which allow charging records to record the time of handover in the case of inter-PLMN operator handover. Charging records must be able to reflect the level of UTRA radio access, operation mode and network type after handover.

A capability to provide network management information relating to frequency of occurrence and type of handover should be defined.

4.3.4 Cost and efficiency

The UTRAN specifications shall facilitate the cost-effective implementation both on the network and on the terminal side, of multi mode operation between GERAN and UTRAN. Impacts on networks based on earlier releases shall be minimised. Such handover shall not require user intervention.

4.3.5 Security

Security requirements should embody the principle that handover shall not compromise the security of the network providing the new radio resources; the (possibly different) network providing the original radio resources; and the UE. The security mechanisms should also cater for appropriate authentication processes and meet the requirements of national administrations in terms of lawful interception.

4.4 Performance Requirements

4.4.1 Temporary degradation of service caused by handover

During intra UTRAN handover or handover from UTRAN to GERAN, degradation of service shall be no greater than during intra GERAN handover.

The duration of the discontinuity experienced by PS and CS real time services should be shorter than that in the handover of CS speech calls over GERAN.