For business group subscribers the prefix for calls outside the business group, the trunk prefix, has previously been transferred in the LUA message or CSU message.

When an MTXV receives a call from a roaming subscriber which has category "Business group subscriber", the dialled code is either a called subscriber number, if the trunk prefix is included, or a short number for a call inside the business group.

If the dialled code is the short number, it should be converted to the corresponding called subscriber number before setting up the call.

After receiving a short number from business group subscriber the MTXV fetches the called subscriber number from MTXH/HLR.

It therefore sends the Business Group Number Enquiry Message (BNE) to MTXH/HLR. The message includes MTXV Identity, mobile station Identity and dialled short code. When sending BNE a timer T9 is started.

When MTXH/HLR receives the BNE is searches for the requested called subscriber number. If a valid number is found, it is sent in the Business Group Number message (BNM) to MTXV.

If MTXH/HLR is not able to find the requested called subscriber number or wants to restrict the call in the MTXV, it returns the Business Group Number Rejected Message (BNR) with the appropriate reason set and terminates the procedure.

When receiving the BNR, MTXV performs the necessary signalling towards the MS and terminates the procedure.

By receiving the requested number in the BNM the MTXV stops timer T9 and continues the call set-up normally using the received number.

If MTXV and MTXH/HLR do not both belong to the same country, MTXH/HLR shall convert a national number to an international number before transferring it to MTXV.

If T9 expires before BNE/ BNR is received, MTXV performs the necessary signalling towards the MS and terminates the procedure.

If no access code is received in the LUA or CSU message the dialled number is always transferred to the HLR for processing. If the dialled number is accepted but not a short number the BNM message is returned to the MTXV without a called subscriber number. If the dialled number is not accepted, the BNR message is returned to the MTXV.

The procedure is illustrated in the following figure.

Figure 3.12: Business group number information enquiry, response procedure.