Ingeniero

Roaming issues analysis



INTRODUCTION



We have seen that the solution provided for Ericsson to allow Sprint roamers to be served for Pegaso MSCs is very restrictive about havingroamers form other companies and different countries, specially when the signaling have the same Clearing House or point of contact with the other roaming partners (this condition is very common sincethe Pegaso necessity for a Clearing House).


With this in mind was necessary to understand in deep how it the AXEs are allowing to Sprint roamers but others roamers.



ASSUMTIONSWe in Pegaso have a very special configuration were IMSIs are carried from the phones, to the BTSs and then to the BSCs and then to the VLR, the VLR record for the phones is created with the fullIMSI, the real IMSI the phone was programmed with (in the case of the oldest handsets the Mobile Country Code –MCC- and the Mobile Network Code –MNC- is filled with zeros) to get the phone registered theVLR communicates with the appropriated HLR but with MIN based signaling. Also the MSC communicates with the HLR with MIN based signaling (IS-41 C) for call delivery, but to send out the Paging RequestMessage to the BSC the MSC must complete the IMSI if not the handset would never answer to the Page and the calls would never be completed.



DIAGRAMS


1 For phone registration2 For call delivery


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DEFINITION OF THE PROBLEM


Both the VLR and the MSC re-create the IMSI based in the MIN received from the IS-41 C signaling network plus the MCC and theMNC associated to the point code from the signaling was received but the cases where this new IMSI doesn’t fit the VLR record stored in the VLR (this record was created with the real IMSI receivedfrom the handset), but this search in the VLR for the record that match with the MIN was received from the signaling is only done for the Sprint roamers, and not for all the roamers.


It would be...