5 Support by "old" MSs

04.913GPPExplicit Call Transfer (ECT) supplementary serviceStage 3TS

MSs which do not explicitly support ECT are not precluded from attempting to invoke ECT. It is however, an operator option to support the invocation of ECT by these mobile stations. Where operators support this option, the mechanism employed to offer the ECT service to these MSs shall be USSD. However, it should be noted that it may not be possible using this mechanism to offer the same degree of service to the served subscriber as described in clause 4.

5.1 Explicit Call Transfer invocation

MS A invokes the service by sending a REGISTER message to the network using a call independent supplementary service (SS) transaction, with the facility information element, indicating ProcessUnstructuredSS‑Request (the MMI is specified in GSM 02.30).

If the invocation of ECT is successful, then after the SS transaction has been cleared, the network shall release the CC transactions.

If the invocation of ECT is not successful, then the CC transactions shall not be released.

MS Network

REGISTER (PD=SS)

———————————————————————————————————————>

Facility (Invoke = ProcessUnstructuredSS-Request (ussd-DataCodingScheme,

ussd-String = <ECT Invocation String>))

RELEASE COMPLETE (PD=SS)

<———————————————————————————————————————

Facility (Return Result = ProcessUnstructuredSS-Request (ussd-DataCodingScheme,

ussd-String = <Successful Text String>))

DISCONNECT/RELEASE/RELEASE COMPLETE (TI=A-B, PD=CC)

<———————————————————————————————————————

DISCONNECT/RELEASE/RELEASE COMPLETE (TI=A-C, PD=CC)

<———————————————————————————————————————

RELEASE COMPLETE (PD=SS)

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – — – – – – – – – – — – – – – – –

Facility (Return Result = ProcessUnstructuredSS-Request (ussd-DataCodingScheme,

ussd-String = <Error Text string>))

RELEASE COMPLETE (PD=SS)

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – — – – – – – – – – — – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE (PD=SS)

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – — – – – – – – – – — – – – – – –

Facility (Reject (Invoke_problem))

NOTE: The text strings "<Successful Text String>" and "<Error Text String>" shall be defined by the network operator. Each network shall define only one "<Successful Text String>" and only one "<Error Text string>" for each error identified in table 1.

For Phase 1 USSD the operation ProcessUnstructuredSS-Request is replaced by ProcessUnstructuredSS-Data.

Figure 6: Invocation of Explicit Call Transfer for non supporting MSs

5.2 Notification to the remote parties

No alternative procedures are defined for sending notifications to remote parties indicating that the call has been transferred.

Annex A (informative): Status of Technical Specification GSM 04.91

Status
of
Technical Specification GSM 04.91

Date Version Remarks

No Phase 1 version

June 1994 version 1.0.0 To SMG#11 for information

April 1995 version 4.0.0 TS approved by SMG#14

July 1995 version 4.1.0 CR 04.91-001 (category F) approved by SMG#15

October 1995 version 5.0.0 SS removed from Phase 2
CR 04.91-002r2 (category B) approved by SMG#16
CR 04.91-003 (category B)

February 1996 version 5.1.0 CR 04.91-A004 rev 1 (category C) approved by SMG#17

December 1996 version 5.1.1 GTS converted to draft prETS 300 958 for Release 96

May 1997 version 5.1.2 ETS 300 958 first edition

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