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  • This topic has 6 replies, 1 voice, and was last updated 8 years ago by Pix.
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  • #69887

    I have a doubt with a scenario.
    But before that I would like to know what happens to SDCCH once TCH is assigned and call is in progress. Does SDCCH gets deallocated,; if not what is the functionality of SDCCH during this period?


    Now, let me discuss about the scenario.
    I have composed a segmented SMS (10 segments) and sent to 5 recipients. Now, if I make a MO call, what are the bottlenecks to be considered here?

    Appreciate if I get answer in terms of respective channels.



    During a call the SDCCH is not used : it was released at the end of the call setup.

    If a call is originated while a SMS is being sent, then, as far as i know, the sending of the SMS will have to finish being transmitted first, then this SDCCH will be released, and then a new SDCCH will be requested in order to perform the call setup.

    The first (SMS) SDCCH was established in order to perform a SMS transmission and only that. It cannot be re-used to perform a call setup.

    I hope i got your question right…


    Thank you for the reply.

    But as per your explanation, once I initiated MO SMS, I cannot do MO call until MO SMS has been completed. Is that right? But I don’t think that’s the case with most of MS’s.

    MS’s are capable of sending the SMS while the call is in progress.

    I read somewhere that once call is initiated, SMS would be sent in SACCH.

    I suspect that SACCH being used for SMS transaction is only used in this sceanrio: “Sending SMS “after” initiating a call.” Am I right here?

    But in my case, I am having trouble to initiate the call during SMS transaction because the SMS’s too big.

    How should I handle this case?


    Also, could MS handle the paging request during this (10 segmented) SMS transaction?


    Related question:
    If call is in progress, then if I were to send the SMS, then SACCH will send the SMS while call proceeds on TCH. But what about the measuring reports that SACCH has to send since it is busy sending the SMS?


    Oh, here are some (good) answers :
    GSM 04.11

    I was wrong before, the SMS should be interrupted in order to setup the TCH call.

    Extract :

    The short message service will be supported by an SDCCH or SACCH, depending on the use of a TCH;
    – When a TCH is not allocated, the short message service will use an SDCCH;
    – If a TCH is allocated during a short message transaction on an SDCCH, the short message
    transaction will stop and continue on the SACCH associated with the TCH;
    – If a TCH is allocated for the short message service, the short message service will use the
    associated SACCH;
    – When an entity using a TCH finishes its transaction, the RR-sublayer may choose to continue an
    ongoing short message transfer on the SACCH, or optionally transfer it to an SDCCH.

    I knew the answer about what happens to the Measurement Reports when the SMS being sent during a TCH call (on the SACCH).

    It’s true that SACCH is already used to transmit MR. So how the hell does the SMS go through… I knew the answer, but i can’t recall… sorry.

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