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SDCCH congestion

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  • #68297 Reply
    slim omrane


    Please to clarify that point :

    In case on SDCCH congestion , Is there a repetition of channel request?Only in case of location update and call reestablishment allowed?
    The KPI SDCCH_congestion rate is thus wrong because it contains redunduncy?

    Please the link for 3GPP clarification

    #68298 Reply

    hi slim,

    if the sdcch is congested, the BSS will behave accordingly to your setting “Enable Immediate Assignment Reject”.
    If “ImmAssRej” = DISABLE then the MS will repeat the Channel Request almost immediately
    If “ImmAssRej” = ENABLE then the MS will repeat the Channel Request only “WI_xx” ms later, which provides more chance for a SDCCH channel to be available.

    The MS can send up to MAX_RETRANS+1 channel requests.

    Yes, the SDCCH Congestion is artificially increased by retransmission. However, if you activate the “ImmAssRej”, you can apply the formula:
    SDCCH_Cong – Imm_Ass_Rej / Channel_Request

    As a result, you are counting only the last congestion failure. If the SDCCH is setup at the 3rd attempt :
    SDCCH Cong = 3
    Imm Ass Rej = 3
    –> sdcch cong rate = 0%

    I hope it makes sense… please test the formula carefully because I don’t remember having tried it.
    (i didn’t care much about artificial SDCCH congestion.. it should always be zero IMO… really and artificially !)


    #68299 Reply
    SDCCH congestion

    Thanks Pix,
    Further clarifications please:
    The SDCCH requests are repeated till max retrans+1 whatever is the type of the service needed (LU,SMS,call establishment)?

    In case of LU,it will stop retransmissions by max retrans+1 or it will do another cycle?

    Please the link of 3GPP doc for repetition of SDCCH requets in case of SDCCH cong

    #68300 Reply

    yes, retransmission works for any kind of request.

    Location update will indeed start a new cycle, because the MS has to do the LU anyway.

    44.018 -> the channel request procedure

    23.122 -> the location update process (i’m not sure whether they say how long to launch a new cycle in this doc).


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