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What type of call drop is this?

Viewing 15 posts - 1 through 15 (of 20 total)
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  • #59446 Reply
    MKT
    Guest

    A strange problem is coming in a city having two BTS.

    One is of ericsson
    One is of Nokia

    You call a number
    call gets connected.

    Conversation is going on

    the call gets mute

    the indication on phone shows that call is going on

    even the dedicated mode parameters are shown on the pocket, like hoping etc

    During this period if anybody calls your number it is unreachable.

    Is it an NSS problem?

    #59447 Reply
    Pix
    Guest

    Hi,

    What happens before the call is muted ? Handover ?
    How long can you hear the voice ? Is it a fixed duration at every attempt ?

    I suspect DTX problem, or ciphering problem, or TFO problem…
    It could be NSS as well … Don’t you see any special message on layer 3 or layer 2 logs just before the muting ?

    cheers,
    pix

    #59448 Reply
    MKT
    Guest

    Yes, a handover happens.

    & then the call gets mute.

    Not all calls are getting mute but many do gets.

    Duration is not fixed, actually i didn’t focused on that.

    yes in ericsson BTS the ciphering is off but in nokia it is enabled. But what does it has to do with call mute at your end but release at other end?

    DTX & TFO , i didn’t get how?

    But one thing is sure, the border where all this mess is going on is having both the cells with more or less equal strengths.

    Could it be some media issue among the two MSC’s i.e. nokia & ericsson.

    Why does the release from network is not reaching the MS?

    How can network control the behavior of MS like, MS get Hanged. Only power off gets it back to network.

    Kindly help as vendor has doing hit & trial.

    Regards

    #59449 Reply
    Pix
    Guest

    Ciphering it is then 🙂

    Try to match ciphering on both sides (by the way, ciphering is mandatory in a GSM network, your subscribers wuld be so p!ssed off if they knew… use A5/1 everywhere.

    I’m confident that everything will work fine after…

    You could try to find why the ciphering is not handled properly during HO, but I think that is a MS issue.

    Cheers,
    pix

    #59450 Reply
    MKT
    Guest

    Thanks pix,

    Let us say Nokia cell= N1

    Ericsson cell= E1

    Today I did the following testing.

    I have two MS , say MS1 and MS2

    I initiated a call from MS1 to MS2 in N1

    The call gets established.
    In the Current channel window

    I can see the ciphering through A5/2.

    Then a handover occurs to E1 (This is an inter MSC handover)

    The handover is successful but one strange thing i observed.

    I see that even though the ciphering is disabled in the whole Ericsson MSC, yet the current channel window displays that ciphering in on with A5/2 in E1, that was strange.

    With in seconds the call gets dropped rather released at MS2.

    But MS1 continues to show the dedicated mode parameters to me in E1 cell.

    We might confuse the case with call muting, but strictly speaking I don’t think it is a case of call muting actually the call at MS2 has been released, I repeat it is not dropped at MS2.

    But the call at MS1 is not release and the MS1 is continuing to show he dedicated mode parameters, and of course the ciphering in a cell which doesn’t support it at all.

    This is a stage where MS1 can be termed as in hang state.

    Even if you press the END at MS1 the only difference it will make is that the indication of off hook will be removed from the display of MS but the call/TS is still shown as occupied.

    The reverse is not true, I mean you initiate a call in E1 and if the same is handover to N1 i.e from a cell where ciphering is off to a cell where cell ciphering in on, such scenario doesn’t happen

    But again if the call is handed over back to E1 the process repeats.

    As per the suggestion of Pix,

    I requested the NSS to enable the ciphering in E1 or rather MSC (as ciphering is a feature at MSC level?)

    After that the same testing was repeated. But the situation remained unchanged.

    After that the NSS person (ericsson) requested that we might test again by disabling the ciphering in both the MSCs i.e. Nokia and Ericsson.

    And we did so to test it again. But again this times also no result.

    Finally we made the situation back to initial i.e. in N1 it enabled but in e1 it is disabled.

    After that I asked about DTX. They said in both the cells it is on.

    In N1 SDCCH handover was enabled, that was disabled.

    But we are back to the square.

    #59451 Reply
    pix
    Guest

    mkt,

    i can’t post my answer. could you please tell me your email ?

    >>> mister webadmin… the word filter is a little strong 🙂

    #59452 Reply
    AliAsgher
    Guest

    Dear Pix,

    Isn’t this case strange. Because I think that in InterMSC HO, HO from Higher to Lower Ciphering modes is possible but the HO does not occur from Lower to Higher ciphering? Not completely sure though

    #59453 Reply
    MKT
    Guest

    manojkumartomar at gmail dot com

    #59454 Reply
    MKT
    Guest

    Pix, I am waiting for your email.

    once again my id is:
    manojkumartomar@gmail.com
    manojkumartomar@rediffmail.com
    Thanks

    #59455 Reply
    Pix
    Guest

    Sent…

    #59456 Reply
    Pix
    Guest

    Hello Ali,

    I wasn’t aware of that, it’s interesting. And what you are saying is that the problem below actually doesn’t look like a ciphering issue, because it doesn’t happen in the right direction ?

    I’m not sure either that it is a ciphering issue, but the coincidence is too big to be forgotten.

    Do you have any other idea ?

    I asked MKT to check the speech codec and TFO in my mail.

    #59457 Reply
    MKT
    Guest

    Problem is solved now.
    Some handover parameter is modified in the Nokia MSC.
    Ciphering was not the issue here.
    Details not available yet.
    Will post them as soon as it is available.

    Thanks

    #59458 Reply
    Pix
    Guest

    MKT,

    Please share your solution when possible … (or send me email if you want to keep details as “top secret” 🙂 )

    I wonder what kind of HO parameter can bug the MS or force a call release… it’s intriguing.

    Best Regards,
    Pix

    #59459 Reply
    AliAsgher
    Guest

    Dear Pix,

    I am sorry but I have no idea on what could cause a MS to hang! I am also very curious on which parameter was changed for the problem resolution?
    Lets wait for MKT to post details.

    Regards,

    #59460 Reply
    MKT
    Guest

    The roots of problem were found in NSS.

    I am sorry for not mentioning during the problem description phase that the MSC that controls the E1 cell is in fact an MSC Server, 3GPP R4 core network.

    May be I am not the right person to describe problem as I said it is in NSS, yet I will try my level best.

    As we know that problem comes only when the MS moves from N1 to E1 or from a cell of Nokia MSC (here it is MSC only and not a MSC server) to a cell of Ericsson MSC Server.

    An Inter MSC handover should occur and it do.

    But this is the trigger of trouble.

    The call at other end gets released, doesn’t matter with whom you are talking be it a landline or a GSM number.

    And at your end you find your phone is hanged. It shows itself to be in dedicated mode.

    Where is the problem? We are finding it difficult to get it done, as we have to deal with two different vendors for a single issue.

    Then one day I got a call from NSS guy that vendor Nokia has solved the issue and I was asked to verify it.

    After verifying when I asked the same NSS person to tell me what was the cause.

    The reply he gave me was that…

    In Nokia MSC the handovers are defined by defining two parameters, GT & SCP.

    In our case the handover is defined with Ericsson MSC server by using both GT & SCP. That was causing problem. When they removed the SCP part and kept only GT part the problem got solved.

    I am not sure whether the person was saying the word SCP or SCCP, whatever it may be but I believe it was a case of SS7 somewhere.

    May be SS7 over TDM when get interfaced with SS7 over IP , SIGTRAN has got its own issues.

    Regards,

    MKT

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