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SDCCH blocking is high

Viewing 15 posts - 1 through 15 (of 62 total)
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  • #45800

    IN ur network SDCCH blocking is very high in boundary cell . We are using ericsson GSM 900 system.
    We increased SDCCH which is in boundary cell still SDCCH blocking is high. We activated Adaptive Configuration of Logical Channels in our network. Still SDCCH blocking high. What will be reasons and how to reslove the issue.


    – check BSIC/BCCH unicity
    – increase the RXLEV_ACCESS_MIN from -104dBm to -98dBm for instance (only for a few hours !!), and observe the result.


    hi vijay,
    please also try the following :
    1. CELL-RESELECT-HYSTERESIS for Location Area selection can be fine tuned.

    2.Check how much traffic the site is taking,if the site is carrying low traffic this can be the case of PHANTOM RACH which can make the SDCCH blocking high.


    Thanks for ur feedback Pix . We tried this option also we set Rx lev min from -105 to -100 dBm.S till we are facing the problem.Can u suugest how to improve as we are facing this issue for long time. We also tried to increase the CRH from 6 to 8 also. still we are having high SDCCH blocking


    is it a “satellite abis” BTS ? if yes, then … well, i don’t know, that can create some delay on the sdcch signalling. what is the average time of sdcch dialogs ?

    – try removing the adaptative configuration of logical channels and set 2 full timeslots for SDCCH (or 3, or 4, test different configurations out)

    – try changing the frequencies

    – try reducing the timing advance filter (instead of 64 (32km), set it to 15 (= 7.5km) for a few hours .

    For info, the RXLEV MIN is different from the RXLEV ACCESS MIN. Beware. First one : for HO. Second one : for Call Setup. Be sure you set the latter to


    I wanna know what all things can be checked for SD drops and also we have not enabled SD to SD handover
    Can anybody help me out????


    hi kaluan,

    most of the time, i find that SD drop is linked to interference from other cells or is caused by a large cell coverage (many subscribers at the cell border, with low RXLEV)

    sdcch HO should be disabled, unless you want to make your life complicated. It will not improve the QoS in the end, so you’d rather leave it off.

    if you want to make a better diagnostic : keep only on SDCCH timeslot, disable frequency hopping, and move your SDCCH timeslot on different TRX. Maybe only one frequency is interfered, or one TRX is faulty, causing trouble on the SDCCH timeslot.



    Can anybody explain me that how sd abis drops happens.Thir is some sites in our network which are having 2000 sd abis drops ,But their are no hardware problems in the cells.


    hi nishant,

    sd abis drops… mmm.. i’d say that the trx which is carrying your SDCCH timeslot is faulty. you don’t see any TCH abis drops ?
    how much traffic does the cell carry ? what is the average call duration ?



    I will give you one cell as example .

    cell is carrying a traffic of 15erl.
    SD radio fails are 300
    SD abis fails are 1600
    TCH radio fail is 15
    TCH HO fail is 20
    TCH abis fail is 20

    SD completion rate is 91%
    TCH completion rate is 98.8%

    their are no alarms in Cell.All the trx’s are checked .

    I need to give a explanation to the implementation team for changing any trx’s.

    Please suggest a solution.


    Check CHAP make it 1 or 6


    Can any body tell the reason of High SDCCH Blocking during early morning hours with excessive Location Update request in few cells


    Hi Danish,

    People get up for work, take their car at 8:30am and go towards the main city at 8:45am. So between 8am and 9am, a lot of location updates occur because many people cross the LAC borders at the same time.

    No parameter or LAC design can fight this (AFAIK !). Be sure to optimize the dimensioning of SDCCH.




    can you please expalin phantom rach!!!


    Da Architect

    Hi Danish,

    I am very convinced with Pix idea. but you can take into consideration that there is a logical parameter to make the MS execute location update if the MS was in IDLE state for 3 or 4 hours (configurable by the this parameter); Example: subscribers sleep at 12:00 midnight after 4 hours the subscribers MS will start generating these Location Updates, which implies in the SDCCH. But truly, that wasn’t a reason for SDCCH Blobking in my network… this return us back to Pix idea, wich is more convincible for your case. you must redimension SDCCH for cells that are on LAC borders.

Viewing 15 posts - 1 through 15 (of 62 total)
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