If an MTXH receives a call to a subscriber which has activated any of the unconditional call services, e.g. the "Immediate Call Transfer", the call transfer is performed by the MTXH.

If an MTXH receives a request for routing information for a subscriber which has activated any of the unconditional call transfer services, MTXH allocates one of its own Mobile Station Roaming Numbers and returns this as routing data (see section 3.9).

The procedure described above will then apply when the call later on is received.

If an MTXH receives a call to a roaming subscriber which has activated any of the conditional call transfer services, e.g. conditional call transfer on no page response, the call is forwarded or re-routed to the MTXV.

MTXV will receive information about the status of the call forwarding services during Location Updating (LUA) or when updating the category/supplementary services (CSU).

When receiving a call to a subscriber which has any of the conditional call transfer services activated, MTXV will therefore have the knowledge of the status of the service, and is able to handle the procedure locally.

MTXV has to fetch the C-number to be used from MTXH. It therefore sends the Conditional call transfer enquire message (CTE) to MTXH. If the duration of alerting included in CTA should be used towards the B-party, CTE must be sent at the same time as alerting of the B-party is started. The field "Type of call transfer" in CTE should in this case always be coded to the value "Conditional call transfer on no answer".

If the duration of alerting is not needed, CTE may be sent when the condition for call transfer becomes true.

If an announcement is to be sent to the calling subscriber, the information about the preferred language to be used has previously been received in the RNE.

When MTXH receives the CTE it checks if it is possible to send the requested C-number. If it is impossible it returns the Conditional Call Transfer Rejected Message (CTR) with the appropriate reason set and terminates the procedure.

When receiving the CTR, MTXV performs the necessary signalling towards the PSTN and terminates the procedure.

If MTXH is able to transfer the requested C-number, it is transferred in the Conditional Call Transfer Accepted Message (CTA) together with the information about the position of the C-number in the list of C- numbers if fetched from a list. If the C-number is an arbitrary number, this is also indicated.

If MTXV and MTXH do not both belong to the same country, MTXH shall always convert a national (significant) C-number to an international number before transferring it to MTXV.

When receiving the CTA, MTXV sets up the call to the C-number given in the message. If necessary, according to the service, MTXV may repeat the procedure in order to fetch the next C-number in a list of C-numbers.

If T5 expires before CTA/ CTR is received, MTXV performs the necessary signalling towards the PSTN and terminates the procedure.

The procedure is illustrated in the following figures.

Personal number service means a conditional call transfer service activated by Administration (in MTX). No announcement is given for the A subscriber, when the transfer is made.

When the personal number transfer is made, no indication of this transfer is set for the forward address messages. Also already transferred call is re-routed as normal and the indication of transfer is not changed.