A new call set-up from the MTXG is received in the HLR/MTXH at reception of a message GEI. When sending GEI a timer T10 is started in MTXG.

Included in the message GEI is the mobile station directory number which is used for addressing the called subscriber and the MTXG Identity and the MTXG local call reference witch together form the global call reference. The global call reference is used by the exchanges that sends SEM for addressing the call set-up in the correct MTXG.

Calling party category and calling party number is sent to HLR/MTXH to ensure that detection of illegal traffic cases or call screening can lead to disconnection.

If called subscriber is roaming an MSRN is fetched from MTXV by the messages HRE/HRM. If the HLR/MTXH is not going to process the call set-up any further (The call may for instance be routed via the MTXH or towards the called party without any more processing by the HLR/MTXH), message GET is returned to MTXG with a routing number. When GET is received in the MTXG, timer T10 is stopped.

To be able to charge the call in the MTXG, information for charge determination and the mobile station Identity is sent to the MTXG.

When GET is sent to MTXG, the procedure in the HLR/MTXH is terminated.

If message SEM is received, message SEA is returned without reporting to the HLR/MTXH.

The basic procedure is illustrated in the following figure:

Figure 3.11.1: Improved rerouting, basic procedure

A new call set-up from the MTXG is received in the HLR/MTXH at reception of a message GEI. Timer T10 is started in MTXG when GEI is sent to HLR/MTXH. If the HLR/MTXH by any reason is going to terminate the call set-up attempt, message GET is returned to MTXG with a proper call termination code. Timer T10 is stopped in MTXG when GET is received.

When GET is sent to the MTXG, the procedure in the HLR/MTXH is terminated.

The basic unsuccessful procedure is illustrated in the following figure:

Figure 3.11.2: Improved rerouting, unsuccessful procedure.

Examples on action in MTXG when message GET is received:

A new call set-up from the MTXG is received in the HLR/MTXH at reception of a message GEI. Timer T10 is started when GEI is sent.

Included in the message GEI is the mobile station directory number which is used for addressing of the called subscriber, and the MTXG Identity and the MTXG local call reference which together form the global call reference,

and is used for addressing the correct call set-up in the MTXG when the GEI is answered.

If the called subscriber is roaming, an MSRN is fetched from MTXV by the messages HRE/HRM. When the MSRN is fetched by the HLR/MTXH, message GRM is returned to the MTXG, as the HLR/MTXH wants further control of the call.

The transaction reference is used to link the GRM sent to the MTXG together with the message GSE. The GSE is sent from the MTXG when one of the call event report indicators previously indicated from the HLR/MTXH becomes true.

The call event report indicators are set according the subscribers services. The call event report indicators "disconnection/termination before B-answer" and "B-answer" are always reported to the HLR/MTXH.

The announcement indicators returned in GRM are set according to the services of the subscriber in question. The call origin information received in GEI can be used to decide whether announcement is to be played or not (may be relevant if the call is coming from IN).

The fact that the routing number may be destined to IN, where a routing prefix and a location number is a part of the number, makes it necessary to have up to 32 digits in the routing number.

To be able to charge the call in the MTXG, information for charge determination and the mobile station Identity is sent to the MTXG:

When GRM is sent from HLR/MTXH, the timer T12 is started. When GRM is received in the MTXG, the timer T10 is terminated.

If an MSRN is used, the call is set up towards an MTXV. Message SEM is sent when one of the report indicators are detected in MTXV. If no page response or base station congestion is received in SEM, an appropriate announcement is played or an IN-specific message is sent further on backwards in the network. SEM is acknowledged by SEA.

If a call event reported indicator in SEM is set, but the corresponding call event report indicator in GRM is not, SEM is acknowledged by SEA without any further action in the MTXG.

When E.g. B-answer is received in MTXG, the message GSE is sent towards the HLR/MTXH to report that the call set-up is completed. Timer T10 is started in MTXG when GSE is sent. The MTXG awaits further orders from the HLR/MTXH. While waiting, no call events are reported to the HLR/MTXH.

When GSE is received in the HLR/MTXH, the timer T12 is terminated. If the subscriber in question does not have any active service, the call set-up is from the HLR/MTXH point if view finished, and GET is sent towards MTXG.

Timer T10 is stopped in MTXG when GET is received. When GET is sent to the MTXG, the procedure in the HLR/MTXH is terminated. This means that further call events detected in MTXG are not reported to the HLR/MTXH.

The procedure is illustrated in the following figures.

Figure 3.11.3a: Improved rerouting, MS updated in MTXV, successful procedure.

Figure 3.11.3b: Improved rerouting, call forwarding, successful procedure.

A mobile network operator can choose to introduce improved rerouting independently of other cooperating networks. When cooperating with networks not supporting improved rerouting, the operator can have call forwarding executed in MTXG based on CTE messages received in HLR/MTXH or any suitable telephony signalling (E.g TUP or ISUP) message received in MTXG.

When a CTE is detected in HLR/MTXH, it is answered with a CTR. The HLR/MTXH reports the relevant call event to the MTXG in a SEM.

Figure 3.11.4: Network introduction of improved rerouting