03.333G security3GPPLawful InterceptionStage 2TS
Figures A12 and A13 show the interception of explicit call transfer. Figure A12 covers the case where one pair of stublines is used per target, figure A13 covers the case where a pair of stublines is used for each target call. The mobile transferring the call (B) is the target for interception.
Figure A12: Interception of explicit call transfer – stublines per target
Figure A13: Interception of explicit call transfer – stublines per target call
In figures A12 and A13 the release of the stublines is done after the transferred call is released by A or C. It is a national option not to support interception of transferred calls. In that case, the release of the stublines is done after the call is transferred and B is no longer involved.
Annex B (normative):
Interception for GPRS