If the MTXH receives a call or a request for routing information for a subscriber which is updated in an MTXV, MTXH has to fetch the information from MTXV in order to set up the call through the PSTN. MTXH therefore sends the Roaming Number Enquiry Message (RNE) to MTXV.

Included in the RNE is the MS Identity and the "Preferred Language" information. The "Preferred Language" information indicates to the MTXV about the preferred language to be used if announcements is to be sent to the calling subscriber when later on the call is received. When sending RNE a timer T4 is started.

When receiving this message, MTXV allocates a Mobile Station Roaming Number (MSRN), starts a timer T7, and sends the number in the Roaming Number Message (RNM).

If this is not possible, MTXV responds with a Roaming Number Rejected Message (RNR) and terminates the procedure. If receiving RNR, MTXH performs the necessary signalling towards the PSTN and terminates the procedure.

The Mobile Station Roaming Number is a number belonging to the national numbering plan. When allocated, it is tied to one of the MS identities served by this MTX. The number is used for routing the call through the PSTN, and when received at the MTXV it also identifies the MS Identity.

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

When receiving the RNM, MTXH either sets up the call using the MSRN, or it sends the MSRN backwards in the network (see section 3.9).

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.

If T4 expires before RNM/ RNR is received, MTXH performs the necessary signalling towards the PSTN and terminates the procedure.

If T7 expires before the call is received, the MSRN is released and may then be allocated for another call.

If a call is received using an MSRN which is not tied to an MS Identity, the MTX returns an unsuccessful backward signal and terminates the procedure.

If more RNE’s are received for the same MS while T7 is running, an RNM should be returned for each RNE received.

If the MS Identity in the received RNE does not exist in the Visitor Register of MTXV, MTXV shall initiate the Location Updating procedure before sending RNM.

The recorded data in MTXV shall be stored for this MS on temporary basis, only to enable correct processing of the call.When sending LUM a timer T8 is started. If LUA/ LUR is not received before T8 expires, the MTXV sends RNR with the reason set to "MS id. unknown".

If page response with the correct MS Identity is received, the MS location has thus been confirmed and the Visitor Register can be permanently updated.

Otherwise, if no page response is received, the MS data shall be deleted from the Visitor Register.

If the call already has been treated by the "IN" when received in MTXH, MTXH may send this information to MTXV using "Call routed via "IN" in the RNE message.

In which way the MTXH will recognise that the call already has been routed via IN is a national option.

In MTXV a possible "call routed via IN" received in RNE will be stored until the call arrives in MTXV. This information is then connected to the call and used when deciding how to handle an unsuccessful call set-up.