The supplementary service shall be provided after pre-arrangement with the service provider.
The provision of the Call Hold (HOLD) supplementary service is also required.
The supplementary service shall be withdrawn at the subscriber request or for service provider reasons.
The supplementary service shall be activated by the service provider as a result of provision.
The supplementary service shall be deactivated by the service provider as a result of withdrawal.
ECT shall be invoked by the served mobile subscriber by use of a control procedure as described in TS 22.030
The served mobile subscriber (subscriber A) who has two calls (one with subscriber B and one with subscriber C), each of which can be an incoming call or an outgoing call, can request the invocation of the ECT supplementary service with respect to the two calls.
The connection shall have been established on one of the calls (referred to as the call between subscriber A and subscriber B).
The ECT supplementary service can be invoked after the connection has been established on the call between subscriber A and subscriber C, and in addition, as a network option, after subscriber C has been informed of the call (i.e. an outgoing call from subscriber A to subscriber C, where the connection has not yet been established).
On successful invocation of the ECT supplementary service, the two calls between subscriber A and subscriber B and between subscriber A and subscriber C respectively shall be removed from subscriber A's access (i.e. the traffic channel and the signalling channel towards subscriber A will be released) and shall be transformed into a normal call between subscriber B and subscriber C where the state of the previously held party is changed to active without a subscriber action.
The previously held party will be informed in the normal way of the retrieve procedure.
If the network option above is supported, then if subscriber C is being informed of the call from subscriber A at the time of transfer, the call shall remain in this state at subscriber C (as a network option the ringing tone will be given to subscriber B), and when the connection is established by subscriber C, subscriber C shall be connected to subscriber B.
Subscriber A will no longer have any control of the on-going call between B and C.
The network shall inform (if possible) subscriber B and subscriber C of the occasion that call transfer has happened including the state (connection established, or user being informed of the call) of the call to the other subscriber.
If the network option above is supported, then after connection is established on a call which was transferred whilst subscriber C was being informed of that call, subscriber B shall be informed that the connection has been established on the call to subscriber C.
The line identity of subscriber B shall be indicated to subscriber C as specified in subclauses 8.1
The line identity of subscriber C shall be indicated to subscriber B as specified in subclauses 8.1
through 8.4, either:
at the time of transfer, if the connection had been established between subscriber A and subscriber C; or
when subscriber B is informed that the connection has been established to subscriber C, if this occurs after transfer.
The charging principles applicable prior to the served mobile subscribers invocation of ECT, shall also apply after the ECT supplementary service is successfully invoked, i.e. the same charging information will continue to be collected after invocation as before. The charging information for both calls shall contain an indication of successful invocation of ECT.