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tch access failure,SDCCH drop

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  • #47244

    hi all
    my questions that what is tch access failure and what is different from sdcch drop,also How can understand it that this tch access failure or sdcch drop.
    thank you for your advice…if you have any document shared with me ı will happy.(


    TCH Access is ability of MS to use TCH. It relates to TCH Blocking, HO Blocking, and Call Setup Success Rate.

    For instance a SDCCH drop can be caused to interference, low coverage (uplink, downlink) settings of bss parameters, or an Abis failure.

    As for SDCCH drop, user side will experience the call is try to connect yet not complete and MS return to normal. As SMS, the SMS won’t be sent out after certain while connected/sending.

    For situation having high TCH Access FAilure Rate, when u make call, after “connecting” you will get call block/reject~ “network busy”.

    For situation having high SD drop, you get immediate reject after press call and connecting.

    Situation can be harder if the site facing both TCH Access Failure and SDCCH drop.


    ı know it and ı have to agree with you but ı want know that when time start (for example immediate assigment tch then access tch or not)so when time start it and finish SD drop, When time start it tch access failure which signal together or system information data seem that its tch access failure,how can ı say… and counters when its percive this..thanks all



    The SDCCH Drop occurs during the SDCCH pahse, which is the phase when the MS and the MSC communicates transparently about ciphering, authentification, etc…

    So, the SDCCH phase ends when the MSC sends the “ASSIGNMENT REQUEST” to the BSC (it is not a transparent message anymore).

    Then starts the TCH ASSIGNMENT phase, until the message ASSIGNMENT COMPLETE is sent from MS to MSC.



    yes, SD Drop counter is located before ASSIGNMENT COMPLETE msgs. After that would be the TCH counters.

    more info, for high traffic BH, SD access rate is high and radio stability is much crutial at this moment. it is fast access within short time period.

    optimising SD drop could be much more difficult than expected. start with RF signal strenght.

    Mohit Dave

    Hi can any one explain what is the different between TCH Assignment & TCH Seizure??

    Suhail Mlik

    Hi Mohit.
    TCH assignment is from BTS end to MS while siezure releates ability Of MS to hold that TCH

    Mohammad Helal

    what is the meanning of paging per second?


    what is the difference between TCH BLOCKING RATE and TCH LOSS RATE?
    Best Regards

    dassougui tadjassir oumar

    after we see the statistic repportement from performence i want to konw ,how the opimization adding the capacity or power of the cell


    What is TCH Norm Seizures in NSN?


    tch_norm_seiz does not mean that the MS is on TCH. It means that TCH has been successfully seized. Some mobiles never appear to the TCH because:
    • the call is cleared by the user (probability is higher if call setup takes
    a long time, and thus DR and queuing can increase this share) or
    • the mobile fails or
    • something else goes wrong.

Viewing 12 posts - 1 through 12 (of 12 total)
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