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Viewing 8 posts - 1 through 8 (of 8 total)
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  • #52385

    HI ALL……..

    A MS in dedicated mode performs the LA on which channel.



    when MS in dedicated, the location update is not performed. After call release, if there was a LA change, then a “normal” LU is trigerred by the MS, on SDCCH (as usual).



    Thanks for reply.

    continue with same subject…..

    A MS can receive SMS in dedicated mode.

    Is it over SACCH?

    How does MS distinguish SACCH information being received is of SMS and not usual signaling. ?

    A MS in dedicated mode can even listen and alert the user that there is a CALL WAITING for him. How?

    Just take a case … A MS in dedicated mode is moving. LAI changes. But MS has not(or he can’t) performed the LA update. But there is an other call waiting for this MS. How will the n/w do this now. Since paging in the former LA will get failed. And there is no question of doing the paging in new LA as MS has not performed the LA update till now.

    Last…. it is interesting that MS in dedicated mode can do it for SMS but can’t for LA update. How ever both SMS and LA update are SDCCH dependent.

    Regardsn and thanks


    hi mkt,

    your conclusion is interesting, i’ll answer it directly. Why we do SMS over SACCH, and not LU over SACCH ?

    well, very simply because there is no need to perform a location update while on TCH. During dedicated mode, the MSC knows where is located the MS at the cell level. If a new call is incoming for this MS, then the MSC can obviously route it through the new cell without any issue. Even though it is not the same LAC as where the first call was initiated.

    There is no need of paging.

    The SMS is indeed send on the SACCH if the user is in dedicated mode. We need to do this because, contrarily to the LU, it is mandatory to deliver a SMS.

    I believe that a second call (call waiting) is an information sent on the FACCH, but i have to check it out. (I had to check it out last time already, but i forgot)

    I hope that helps 🙂 Just a thought : i wouldn’t want to be the guy who crosses a LAC border while talking on the phone, and also receiving a SMS and getting a SECOND call. what a life !


    Thanks for reply….

    In dedicated mode MS doesn’t performs a LU as he doesn’t need for it….why?…You said MSC knows the cell where MS is.

    But I have a doubt….

    MSC is not always informed about handovers. This is particularly with the cases which involved intra/inter cell(same BSC) handovers. However MSC is
    involved with the inter BSC handovers.Or you can say in the latter case MSC will know the cell location of MS. The radio resource management is entirely a jurisdiction of BSC.
    It is a usual practice to keep one BSC area as one LA. Hence on highways change of LA in dedicated mode is quite often.

    For call waiting there will be no paging. agreed!!
    Paging can’t be possible. As i have said there are chances of it getting failed( MS in dedicated mode has entered a new LA). So how to do it. Obliviously through signaling. It can be SACCH or FACCH(i don’t know) but it has to be one out of them. MS will not change the previous TCH(call in progress). But pressing a button on MS will acknowledge the MSC and the only switching will take place will be at MSC only. BSC and BTS will remain transparent through out the exercise. I hope it works this way. Please correct if it is wrong.



    the MSC knows the new cell, thanks to the message “HO PERFORMED”, which is sent from BSC to MSC after the handover is succesfull finished.

    regarding the handling of a second call, i don’t know.. it should be explained in 3GPP. In my opinion, the paging is not needed : the MSC will send one message on FACCH (or SACCH) such as “Call waiting”, or something.

    In this situation, and in my opinion, there is no need for paging, authentication, ciphering, call setup, alerting, …


    Dear all,

    Why the MS ask for the “normal location” even the old cell and serving cell have the same LAC?

    In my understanding,
    in the same LAC we will see the LU from IMSI attached and Periodic location update/
    in the differrent LAC we will see the LU from normal location update.

    Thank you for your answers. 🙂



    check out 3GPP 23.122
    NAS Functions related to MS in idle mode

    An LR request indicating Normal Updating is made when, in idle mode,
    – the MS changes cell while being in the update state NOT UPDATED; (for MS capable of GPRS and non-GPRS services when at least one of both update states is NOT UPDATED)
    – the MS detects that it has entered a new registration area, i.e., when the received registration area identity differs from the one stored in the MS, and the LAI or the PLMN identity is not contained in any of the lists of “forbidden LAs for roaming”, “forbidden LAs for regional provision of service”, “forbidden PLMNs for GPRS service” or “forbidden PLMNs” respectively, while being in one of the following update states:
    – UPDATED;
    – the Periodic Location Updating Timer expires while being in the non-GPRS update state NOT UPDATED (triggers Location Updating);
    – the Periodic Routing Area Update timer expires while being in the GPRS update state NOT UPDATED (triggers Routing Area Update);
    – a manual network reselection has been performed, an acceptable cell of the selected PLMN is present, and the MS is not in the UPDATED state on the selected PLMN.
    Furthermore, an LR request indicating Normal Location Updating is also made when the response to an outgoing request shows that the MS is unknown in the VLR or SGSN, respectively.

    I would say it has to do with GPRS state…? But as you see, there are several possibility for a LOCATION NORMAL UPDATING.


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