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Call flow for international Roaming

This topic contains 75 replies, has 0 voices, and was last updated by  Gaurav 10 months, 2 weeks ago.

Viewing 15 posts - 1 through 15 (of 76 total)
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  • #38062 Reply


    Hello Everyone,

    I am trying to find out the call flow for internation roaming mobile. The inital LU and mobile registration part of it. I need this info to arrive at a design to intercept the query of visiting n/w towards the home n/w when a international roamer tries to activate the mobile services.

    I hope someone can throw some lite on the call flow(if possbile with messages).

    Roamer 🙂

    #38063 Reply


    The first thing which happens when a Roamer tries to latch onto a vstd network is
    1) Send Auth Info message is sent to the HLR.
    2) On success of SAI an UL is sent to the HLR. The HLR checks the aunteticity of the VLR(the roaming agreements and stuff) and sends back Insert Subscriber Data which has the Subscriber Info including CSI information, Call Fwd Call Bar etc.
    3)The old VLR is sent a cancel Location by the HLR.
    4)The Insert subscriber Data(ISD) may contain multiple messages. The VLR sends ISD ack for each one of them.
    5)Finally an UL-Ack is sent by the HLR for successful completion of the transaction.
    If the HLR finds that the UL has come from a fraud/non partner network it sends a UL reject for the same.

    #38064 Reply


    Hi Anant,

    Thanks for replying. I also read up the gsm 9.02 spec and figured out that MAP UL message that goes from VLR (of visited n/w) is the message that I am intersted in. What I couldnt figure out was that how is this message routed to home HLR, say for example, visited country is Singapore & home country is Malaysia. So how does the VLR in Sinapore figure out the HLR of home service provider in Malaysia?

    Is it based on IMSI? if so how does the routing happen? Based on GTT?


    #38065 Reply

    celcom’s guy

    hi manul…

    base on IMSI and GTT..


    #38066 Reply


    Yes, it is partly based on Imsi. The imsi contains the MCC & MNC of the network. The VLR derives the CC-NDC from this MCC-MNC pair and replaces it with the CC, NDC.
    So only the first few digits of the imsi is replaced, and the message gets routed to the GMSC of the home network, with the SSN as the HLR.
    I guess this is how it takes place.
    Am i right celcom?

    #38067 Reply

    celcom’s guy


    u a’r right men…

    #38068 Reply


    Hi celcom,

    Which vendor’s equipment are u working with ?


    #38069 Reply


    Hi Manul,

    There will be IMSI Analysis Table where IMSI Format ( E212 ) will be transformed to E214 Format,which will be used for Routing the message to HPLMN.

    E212 IMSI – MCC+MNC Will be Replaced By

    E164 – CC+NDC

    Result = E214 = CC+NDC+Remaining Digits in IMSI.Called as MGT-Mobile Global Title.

    In the MAP-UL Message this will be used as called address.In the same message Full IMSI will be there.Which will be read by HLR Properly.


    #38070 Reply


    hi STM

    3 vendors, alcatel(E10, Nokia(DX200)… and Ericsson. for ericsson i’m not so much exprience in terms of hands on. Only attending the tranning…:).

    how about your’s.

    #38071 Reply


    One thing to remember in terms of I(international) and N(national) after the E series. and also be careful GT translation numbering, you might be delate some of digit and also delate all.. :)…expecially to match with country MCC-MNC and CC-NDC


    #38072 Reply


    Hey guys,

    Thanks for helping me out. Along with the information u provided and the specs, I was able to resolve my queries. I look forward to participating more on this excellent forum.


    #38073 Reply


    Hi there,

    MGT Defintion depends upon each Operators Raoming Data Specification.

    Hi celcom & manul,

    Do you work in ANSI IS41 MAP Enabled Networks ?


    #38074 Reply


    Hi celcom,

    me using ericsson.

    #38075 Reply


    Hi STM,

    What is the Processor type and HW Type ?


    #38076 Reply


    Continuing my quest towards resolving the international roaming problem:-)

    1. Once the Subscriber info has been sent to the visited n/w, in what other scenarios (barring another LU) is the home HLR contacted by the visted MSC/VLR?

    2. Is there some way of preventing the billing info to reach the home service provider and instead route it to a 3rd party.

    3. Does the visited HLR know, at any point of time, that a international roamer is in the network, or does the home HLR is the one point contact for any subscription info that the visited MSC/VLR may need? Incase there is any info in visited HLR, what is it & how is it updated?

    Some of it may not be technically possible, if anyone can provide comments on the above mentioned design concept and throw some light on the questions it would be very helpful.


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