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Subscriber unreachable

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  • #65183 Reply

    Hi, everybody!
    In my network is problem with paging. Sometimes when someone calls to subscriber both TMSI and IMSI pagings goes without answer and subscriber is diverted to IVR. After few seconds SMS about missed call is sent and TMSI paging again goes without answer but IMSI paging is answered. Coverage and quality are good, no congestion on any interface, LAC is small, MS in middle of it, small number of paging discards, no “standart problems”.
    Problem happens seemingly sporadically, both for GPRS attached and only CS attached phones. Happens everywhere in network. So I need your help to guide me to root of it.
    I think that problem is somewhere in MSC and probably with TMSI because we have a pretty high Second paging success rate. Maybe network gives an MS invalid TMSI change timers or counters (from other hand VLR is responsible for TMSI change not MS for statical, allways switched on MSs).
    In short – I am out of ideas so, please, give even your most wildest ideas.

    #65184 Reply


    just one question, before the wild ideas 🙂

    how did you detect this problem ?
    can you reproduce it with your drivetest MS ?
    does this problem impact any kind of MS ? or just a specific brand ? or just the “DTM” MS ?

    wildest ideas
    1/ the MSC is paging a MS with a TMSI that the MS has forgotten -> check if there is such a timer in the MS ? decrease your T3212 or increase the t_purge in the vlr
    2/ the paging request is sent to the wrong LAC, and the second IMSI paging is sent to more LAC’s, including the correct one. -> check your LAC definition in MSC ?
    3/ paging sent in the wrong paging group (air interface)
    4/ … i’m out…


    #65185 Reply

    Thanks for your quick answer!
    I detected this from customer traces on A-Interface and checked also on radio part traces and also expierenced this situation myself. Phone manufacturers are different.
    I can’t reproduce this with any phone. Even after I received SMS and checked traces for my phone I coudn’t reproduce it. Regarding DTM I haven’t checked because it’s not activated in our network but it could be.
    1. This sounds good. I will check it. (t3212 and v_purge are ok, but I agree that there probably is some other network specific MS timer)
    2.From A interface traces is seen that paging is send to correct LAC. With definitions everything is ok.
    3.Also could be but I have no idea how to check it.
    4. I’m too 🙂

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