In case of a call or request for routing information for a subscriber which is updated in an MTXV, information has to be fetched from the MTXV in order to set up the call through the network. HLR/MTXH therefore sends the message HRE to MTXV.

Included in the HRE is the MS Identity and the global call reference. The global call reference is used to be able to address the call control point in the MTXG or MTXH and inform about predefined actions during the call. The global call reference consists of the MTXG Identity and the MTXG local call reference. When sending HRE a timer T11 is started.

When receiving message HRE MTXV allocates an MSRN, starts a timer T7 and returns the MSRN in the message HRM. If sending of HRM is not possible MTXV responds with HRR and terminates the procedure. Reason for not sending HRM may be "no free MSRN", "MS Identity unknown" or "The called subscriber is busy".

If MTXV and HLR/MTXH does not belong to the same country, MTXV shall always convert the MSRN to an international number before transferring it to HLR/MTXH.

If the MS-Identity in the received HRE does not exist in the visitor register of MTXV a location updating procedure as described in chapter 3.7 must be initiated.

When HRM is received by HLR/MTXH ,the timer T11 is stopped. MTXH either sets up the call using MSRN or sends the MSRN backwards in the network. HLR always sends the call backwards in the network.

When MTXV receives the call which is using this MSRN, it stops the timer T7 and sets up the call to the MS Identity tied to this MSRN. The MSRN may now be released and used for another call.

The call set-up is continued and in case of "No page response", "Base station congestion" or when ringing is started in the mobile station, the message SEM is sent according to the global call reference received in HRE. SEM is supervised by timer T13 and acknowledged by SEA.

When SEM is received in MTXH or MTXG the call is disconnected (either in normal way or with specific messages to IN), an appropriate announcement is played or one of the conditional call forwarding services are initiated. Disconnection of the leg towards MTXV is initiated before SEA is sent towards MTXV.

Unconditional call forwarding is handled in MTXH.

Conditional call forwarding may be handled in the MTXH or in the MTXV. The procedure is to be decided by the operator.

The activities for the conditional call forwarding services are not sent to the MTXV as the call forwarding is to be controlled by the MTXH.

A call to a subscriber is routed to the MTXV as described in chapter. 3.7.

The call is controlled by the MTXH and the conditions for call forwarding is supervised according to the following table.

Figure 3.10.1.1: Conditional call forwarding in MTXH, successful procedure

The activities for the conditional call forwarding services are sent to the MTXV as the call forwarding is to be controlled there.

A call to a subscriber is routed to the MTXV as described in chapter 3.10.

MTXV has to fetch data for duration of alerting and relevant C-number to be used from HLR/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.

When HLR/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.

Figure 3.10.1.2b: Conditional Call Transfer in MTXV, unsuccessful procedure.