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Low Util high blocking

Viewing 7 posts - 1 through 7 (of 7 total)
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  • #49938

    Dear all,

    I found some cells have high blocking but low utilization in our network. Why? Any idea? Do we need to expand TRX? Thanks b4..


    check the usage (TCH traffic erlang) per TRX, and check your hardware is “available”. Maybe some of your TRX’s are down –> a cell with 4 TRX has a capacity of 21 erlangs, but if only 1 TRX is available, with 3 erlangs of carried traffic, you’ll have a high congestion rate.

    Also, check your GPRS traffic.. the gprs might be using some of the TS, reducing the voice capacity of the cell.

    low usage, high blocking : before deploying more TRX’s you must ensure you are using your existing TRX as much as you could.

    Can you give us an example of traffic erlang at busy hour for one cell (and what’s the config of this cell)



    How about these datas :
    Config cell: 4 TRX
    TCH carried: 9.93 E
    TCH Blocking = 51.69 %
    Utilisation with GOS 5%=43.42%
    SD Traffic = 8.1 Erl
    SD Blocking = 1.584 %

    How do you think?


    Hi, RRK.

    Could you check for me, how many TCHs we need to achiеve 10 Erl and 50% blocking fallowing the Erlang formula ( table )?

    The SDCCH traffic impress me…
    Do you know the reason for it ?




    oh, i missed this thread… sorry RRK, and thanks TNS to bring it up 🙂

    with 4 TRX, you should get:
    TCH capacity = 21 erlangs
    SDCCH capacity = about 8 erlangs (if 2 ts SDCCH/8)

    Therefore, it looks like there is a mixup between the SDCCH congestion and the TCH congestion. Are you sure about your indicator’s formula ?

    If formulas are right, then what is your timeslots configuration ? (how many TCH and how many SDCCH ?)

    with 9 erlangs, in order to reach 50% congestion, i’d say about 10 or 12 timeslots are working as TCH timeslots.

    and with 8 erlangs in SDCCH and only 1.5% cong, it sounds like you have 3 ts SDCCH/8 which are up and running.


    There is alternate formula that you can use to calculate if you need to re-dimension the site or not. If assuming 50% of your traffic is blocked then add 5 Erls in your current traffic and recalculate utilization at whatever GOS you require at. If the new value is below 100% then you do not need to re-dimension. Check also on which layer you have blocking and more traffic, maybe in some cases you have blocking on 1800 layer while your maximum traffic is on 900 layer. Check for availability of 1800 TRXs etc.


    ho yes, if your cell has an inner zone and an outer zone, maybe only the outer zone is carrying traffic. in this case, check your parameters of HO outer–>inner.

Viewing 7 posts - 1 through 7 (of 7 total)
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