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How to retrieve IMSI of in-bound roamer

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How to retrieve IMSI of in-bound roamer

I would like to understand, how the IMSI of an in-bound roamer be retireved in VPLMN ?

I am working on a LBS node, and would like to retrieve IMSI by using MAP service of inbound roamers, so that I can query the MSC for location for that IMSI.



You can use MAP operation : Send Routing Info to the HLR, which returns IMSI, and Servicing MSC.


MAP ATI is useful but with limited accuracy...

But MAP-ATI and MAP-SRI will

But MAP-ATI and MAP-SRI will be used when we can connect to the HLR of the subscriber.

What do we do if my LBS application is only connected to the HLR which is V-PLMN, will V-PLMN HLR have any info about in-bound roamer ?


Definitely VPLMN's HLR will

Definitely VPLMN's HLR will not have any info about the in-roamer.

Assuming you know MSISDN of the in-roamer, you should be able to query home HLR from anywhere in the world, for IMSI. SRI or SRI-SM you should be able to use even with out being in home network. But ATI is might be blocked in some networks.

One more way is, by monitoring the SS7 roaming links, you should be able to tap and analyse the Loc update etc operations.

In-bound roaming

The LBS app do know the MSISDN and it can send MAP-SRI-SM as well, but how will the message be routed to the HLR of the subscriber that is in some other network ? Which V-PLMN node will update the SCCP called party address and route the message to H-PLMN of the subscriber ?


GT Routing

Use the SCCP called party as MSISDN + SSN (HLR=06)
It will be routed to HLR. There will be a GT translation table in MSC (gateway) which will route the message to the called party network.

Will the calling party SSN be

Will the calling party SSN be validated anywhere ? Will the G-MSC route LBS SSN (145)'s MAP-SRI-SM to other network based on CalledParty GT digits ? What I want to understand is do we have to set any extra flag or do special handling ?



The calling party SSN is not validated anywhere in specific, but its imp to give the correct one to be able to recieve the response. The routing of request doesn't depend on it, but the response does.

Apo AYIVON's picture
help get a project topic in GSM

and how to handle it


CellID information of inbound roamer.


Will SRI-SM return CellID information of the inbound roamer ? If not then how can CellId info be retireved from HPLMN-HLR ?


SRI-SM returns IMSI and serving VLR not the CellID, you have to use ATI , if cellId has to get from HLR


Inbound roamer

Thanks, as earlier suggested ATI might be blocked by some networks. Can MAP SRI message be used from V-PLMN to query H-PLMN HLR for CellID ,IMSI ? Will the SRI message be routed to the H-PLMN and response routed back ?


Yes SRI for SM can be used for getting IMSI. But SRI for SM will not provide CellId. Mostly cell id is blocked for outside network. Even IMEI lookup too.

afink's picture
Re:How to retrieve IMSI of in-bound roamer

If your inbound roamer registers on your network, the only thing the visited network knows about is its IMSI number. So the roamer is identified in the VLR by its IMSI which triggers the initial LocationUpdate message to the home network. So I don't understand why you want to retrieve an IMSI while your roamer registers with an IMSI already. If you want to send the roamer welcome SMS messages or the like, then you need to write an application which monitors the LocationUpdate packets to the home network. This can be passively.

SS7 , Internet & Networking Expert.
Developed own SS7/Sigtran/GSM protocol stack