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Roaming border problem

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  • #55967


    we face problem with roaming with adjacent (border) countries.

    where our subscribers find themself accidentally roaming on networks in adjacent (border) countries, even while the home operator’s network coverage is still available.

    so, do you have any idea how we can prevent this problem. what is the necessary adjustment in our network.

    any idea or solution.




    A mobile phone is going to roam only if it has lost its home coverage, or if the neighbor cell from the other country provides a better coverage. The second possibility would be an inter PLMN reselection, and I’m not sure whether it’s possible or not ๐Ÿ™‚ Anyway, we can try to avoid reselection.

    So why are your subscribers loosing your coverage ?

    1/ BTS is down
    2/ Wrong cell selection / reselection settings (check RXLEV ACCESS MIN value, should be around -110dBm at country boarder, increase the CELL RESELECT HYSTERESIS up to 10 or more dB)
    Also, you might want to increase the Cell Reselect Offset. Perhaps the other operator have increased its CRO so much that their cells pull your MS’s out of home PLMN. As I said before, that would be an interPLMN reselection, and I don’t know if it exists or not…
    Or perhaps I did, but then I forgot ๐Ÿ™‚

    Have you perform a drivetest in this area ?

    I assume you declared the neighbor cell (from other country) as a proper neighbor ? If yes, during a drive test, you can see why a MS would leave your home coverage. Contact the customers that complain, go to their house, and see why it’s happening to them.


    Dear Pix

    we did the drive test, the MS change the network suddenly.



    You should explain a bit more if you want more help.


    Hello RASH
    did you mean that there was good RX-Lev but with that the MS reselected other operator??
    I phased like this problem with very low signal (Same and different MCC)!!! did this happen with the same reasons??



    Dear, Pix and RASH!
    There is no notion “PLMN reselection”. There is only new-PLMN selection procedure, that triggered by overall loss of previous PLMN coverage (no suitable cells in previous (i.e. home) PLMN).
    After new-PLMN selection in different country PLMN,MS is staying in that PLMN until any suitable cell exists in it, even the home network is already available.
    RASH, you can prevent this problem by preventing your subscriber to register in that PLMN, or by expanding home PLMN coverage.


    Dear pan

    we add new site in that area to expand our coverage. I hope this solution will be effective.

    and I find another solution , which called border gatway. and the othar one is base on HPLMN timer, do you have any idea about it.


    Hello Pan,

    I wrote an answer, but it didn’t get published..

    Still, something is not clear…

    There are inter PLMN Handovers which are possible, and so are inter PLMN cell reselections. If both handovers and reselections are possible, it means that you shouldn’t wait for a total loss of coverage before going to another PLMN… In 3GPP, it says that a loss of coverage is one reason for triggering an interplmn reselection. But if the interplmn neighbor is described in the SI5/SI2 messages, wouldn’t the MS be tempted to do the reselection?

    That’s an open point, I’m still looking for the answer..


    This HPLMN vPLMN select/re-select coverage discussion reminds me of another thread a year ago:

    3gpp TS 22811-720 6.12

    6.12 Network selection in border areas
    A problem exists for mobile users when commuting across national borders. Whilst manual network selection may be used to ensure that the user can select the HPLMN / EHPLMN, many users use Automatic Selection mode; and the ME is only permitted to select PLMNs of a higher priority within the same country in automatic mode. This leads to the situation that, having crossed back into its home country and within HPLMN coverage, an ME might remain camped on the VPLMN in the adjacent territory.
    As a consequence, the user will be charged international roaming rates for all calls made or received until such time as he either
    (a) moves out of VPLMN coverage or
    (b) manually selects the HPLMN.

    Note: The power cycling the ME does not solve the problem because the mobile will look for the RPLMN.


    Yes, paraHO, we discussed this problem earlier ๐Ÿ™‚
    Dear, RASH! I heard about border gateway in relationship GPRS only. How will you intend to use this network element in CS-network?
    As to HPLMN searching timer, then it is useless in your case (when Visited PLMN is other country PLMN). MS take HPLMN timer in account only in its Home country.
    Dear, Pix!
    There is an inter-MSC handover – not inter-PLMN. The cell reselection procedure is applied only to cells which belong to selected PLMN (i.e. MS will check MCC-MNC this cell before using it as cell reselection candidate).
    with BR, Pan.


    there is inter PLMN HO in alcatel-lucent. That’s a special feature. It is possible ๐Ÿ™‚


    Yes, Pix,
    I really found out the mention about this feature in 22.129 since REL 4. As in rel-7 said it is an optional feature to implement and as I seemed, this feature not designed completely up to rel 7 anyway, because there are many “open points” on Inter-operator Handover recognized in 22.129.

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