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SD Mean Hold Time

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  • #68394

    Hi, SDCCH Mean Holding Time for my BSC is quite high (~7.5 sec). Is there any way it can be reduced? I am adding SDCCH channels on cells with high number of SD dynamic reconfig attempts, but are there other solutions?



    Here are some leads…

    What is the main usage of SDCCH for this cell ?
    LU ?
    SMS ?
    Call setup ?

    Are you experiencing a lot of SDCCH Drops ?

    Have you tried activating SDCCH HO ?



    Hi Pix,

    The highest share is for MOC. LU is a bit higher than MTC, but MOC is about 3 times that of LU.

    SD Drop Rate is also not that high.

    I have not activated SDCCH HO; will enabling SDCCH HO help in any way?

    I am thinking that reducing LU in some way might also help in decreaseing the MHT, but isnt SD Hold time for call setup higher than that of LU?


    that’s an interesting issue..

    can you do an A trace ? it could be interesting to see which part in the SDCCH phase is “slow” for that BSC.

    Could you perhaps isolate some specific cells with high SD duration within this BSC ? Or are all cells having the same SD duration ?

    If only few cells :
    do you face TCH CONGESTION ?
    could you check your TCH QUEUING counters ? (duration, usage, etc.)
    what is your setting for T11 and T11 forced ?

    If all cells :
    I think the A trace is the only way to understand what is bugging the BSC.
    – could you check processor load ?
    – N7 load ?

    I’m out of idea…
    the SDCCH HO is not a good idea (i think), because it doesn’t take into account that the problem is on the whole BSC.
    If only on few cells, yeah, that’ might worth a shot.



    HI Pix,

    Thanks for your inputs.
    The MHT is not high for all the cells of the BSC but for most of the cells.
    There are 30 BSCs in the network, and MHT ranges from 3.5 sec to 7.5 sec (highest for this BSC).

    Yes, there are quite a few TCH Call queuing attempts; shall I activate HR on those cells to eliminate queuing attempts and reduce MHT?

    The OMU/BCSU/MCMU load for this BSC is just a little higher than that of other BSCs.

    I am also trying to extract the setting of T11 and T11_forced but these timers are not modifiable, no?




    yes, T11 & T11 Forced are changeable.

    If you reduce this duration, you might see that the SD Duration reduces as well.

    Long SD Duration is not a problem as long as the SD is not congested.

    Anyway, if you can prove that the long SD duration is linked to TCH queueing, then you have to work on the root cause : not enough capacity in your cell.
    -> increase/activate HR usage
    -> activate Forced Directed Retry (share load with neighbours, based on L RxLev Ncell DR defined in the neighbours)
    in the congested cell : EN_FDR = enable
    in the target cell where you want to send the trafic load : L_RXLEV_NCELL_DR = -75dBm
    by decreasing the value (ie -80dBm), you will further enhance load sharing effect.

    -> activate Fast Traffic HO : a rather difficult parameter / i don’t recommend it right now.

    -> activate Traffic HO : easy tuning !
    EN_Traffic_HO in all your cells, tune the HO_MARGIN_DEC to be equal to the HO_MARGIN_INC (for example, both = 6dB) every where in your network.
    Then tune high traffic load and low traffic load.
    Don’t set the low Traffic load too low, otherwise it won’t work.
    For example : H_T_L = 85% and L_T_L = 60%

    ok, that’s about it…
    have fun 😉

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