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  • #65969

    when you call a number, you hear the announcement that ,’mobile subscriber is switched off or out of coverage area’ though the phone is not off. The call goes through after several tries. What could be the cause ?


    >Mostly this is related to poor Radio coverage, then wrong cause code Mapping.This can be due to sending wrong cause code by BSC or MSS.
    >IF your call uses TMSS with alternative path it is common to see such behavior. for example your node is connected to two TMSS A and TMSS B – Mapping in TMSSA is wrong but in TMSS B is correct,considering Subscriber is out of reach or cant response to Paging whenever your call established from TMSS A your hear CALLED IS POWER OFF and when via TMMS B you hear Real announcment, and when it is established normally it is ok 🙂
    Mapping is a big issue especially between two oprators , currently we have found out this problem too in our Network
    Hope it comes in use 🙂


    could you please explain a little bit more.
    i am an RF engineer and don’t understand most of what you re mentioning.
    what is the TMSS?
    and pls explain wat u said a little bit more. thanks in advance.


    First let us separate the two voice message:
    Mobile Subscriber is switched OFF – the message is active when the VLR successfully received the IMSI Detached message before the Mobile power down. Or this message can also be activated if the mobile failed to perform Location Update (LU) on a specified period of time. this scenario is also know as “Implicit IMSI Detach”.

    Mobile Subscriber is Out of Coverage Area – The message is activated if the MS does not perform IMSI detach but cannot be paged by the network. I have personal experiences of these cases whenever me and my friends go for outdoor adventures, like trekking, camping..etc. :). Wherein we are being served by Multi path fluctuating signals.
    So, to hear both voice messages in consecutive call attempts is really something to investigate.

    I think MSS is the same as MSC – Mobile Switching Center.

    By the way Bob, it is very intriguing to raise the Mapping issue between 2 operators.
    But the way your explanation goes, it seems that the mapping issue is internal to any of the operator, between their BSC and MSC code Mapping alone. The voice messages are pre-determined independently from each operator.



    it hink yoyo is receiving only one message : “mobile subscriber is switched off or out of coverage area”. Not one and then the other, alternatively.

    Bob :
    your scenario is quite complex.. if you have time, i’d be glad to get some more explanations…

    TMSS = ?
    Is it related to the A-flex feature ? One BSC connected to a pool of MSC’s ?

    Could you detail the “code mapping” principle ?



    Let me give here another example:
    These cases are my real experiences when I worked with another operator. I hope they could draw a picture
    Prepaid SUB A in MSC-S is called, MSC-A dose HLR enquiry, after all it receives PRI (provided MSRN) with CFN (Call forward Num) in Out of reach or OFF situation. Now paging receives no answer–>now call forwarding is processing but before it, IN should be trigged to check balance. Unfortunately she doesn’t have money as usual 🙂 Here IN has not been correctly configured to create a cause with proper announcement. So sends something to mss indicating “hey MSS stop this procedure, her balance is 0$”! Now MSC knows, should return a reason to originating MSC by ISUP message- now MSC is wondering which causes code should be used? In fact MSC should do a mapping between CAP and ISUP. The best solution is using this cause code for ending this call –> Release due to other failure. Hey IN this is not a real reason, then I asked IN Guys to consider this Situation and they did it. Now if somebody calls her, correct Announcement with proper cause code will be sent and played.
    Another Example–>Sometimes you call your fiend Homed in another operator –> paging is unsuccessful due to some reason in BSSAP. Now it is time MSS does a Mapping between a BSSAP’s causes to ISUP message and sends it back to originating MSC (your PLMN ) BUT there is no correct mapping between BSSAP and ISUP or ISUP can’t support such cause code so you receives RELEASE – Normal Unspecified. Oh my god what is the reason??
    This also happens between MAP and ISUP cause code, usually interconnection between two operators use some TMSC (Transit MSC) like Gateway. We use 6 in our biggest city, when I keep calling a subscriber who is out of reach or off some nice scenarios happen. You can do an interesting job to validate another operator, forward another operator MS to a wrong number and keep calling to it , let see what happens  especially if you use more than 1 TMSS or GMSS
    Sorry if I couldn’t explain well due to my poor English and knowledge


    Hi Pix,
    As you know A-flex can be implemented in MGW or BSS anyhow BSS will see just on MSS with one SPC. you know we have One pool with 20,000,000 subscribers!!! what a big amount of LAI or CGI should be defined in MSS in pool , ops just wasting of time – But really MSS in pool has improved our KPI , like as PSR.
    I see cause code as any reason which ends the call,Normally or Abnormally. IN BICC, ISUP it comes up with RELEASE.Here is another definition:
    The call control signaling of each type of protocol (such as ISUP, BICC, and SIP) defines its own failure cause codes. The device at one end generates a failure cause code and sends it to the device at the other end through signaling. Then the connection to the device at the other end is affected greatly.

    By the way Nokia and Ericsson guys consider it as End of selection(EOS) – Huawei: Failure Cause Code (CV) 🙂

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