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LAI planning among BSC

Viewing 13 posts - 1 through 13 (of 13 total)
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  • #52631

    Hi there !

    It is always said that “it is adviced in GSM networks to have 1 BSC for 1 LA”.

    What are the troubles incurred when this rule is not respected ?

    and What is the most “dangerous” ?
    – to have 1 LA crossing many BSCs, or
    – to have 1 BSC that comprises many LAs ?

    Thanks !

    I just discovered this forum, it’s great !!!


    hello skippers,

    and welcome aboard 🙂
    1 BSC for 1 LAC is not a good advice ! You will certainly overload your radio PCH channels !

    You can have several LAC’s per BSC. It depends on 2 things :
    how many paging/s can be processed by one cell at max ?
    how many paging/s can be processed by one BSC at max ?

    One BSC will have to process all the pagings towards its LAC’s.
    One cell will have to transmit all the pagings of its own LAC.

    The worst is to split one LAC over several BSC’s. That’s a terrible idea !

    If you don’t do that, then it is possible to put 2, 3 or 4 LAC’s per BSC (depends on your BSC paging capacity).

    Typically, design about 125 cells per LAC (all cells in the LAC with a non-combined BCCH, and 5 PCH blocks). And if your BSC can support 250 cells, then design 2 LAC’s per BSC. 2 LAC’s of 130 cells each per BSC.

    You could do also 85 cells / LAC and 3 LAC’s per BSC.

    With better/newer BSC, you could go up to 4 LAC’s with 125 cells per LAC, etc. It depends. Check your specs.

    But never split one LAC over several BSC’s, please ! 🙂


    Mr Pix,

    Thanks for your limpid reply.



    I agree with PIX, but dont forget that 1 LAC/1 BSC will be very effective if you know exactly where is the LAC boarders between the BSCs where the minimum HOs (Incoming,Outgoing) are happening between the sites on the boarders sepecially in the inter MSCs HOs…


    Toto, one LAC per BSC … it’s normally not recommended. The PCH in your cells are going to be overloaded, with normal assumptions regarding paging load.

    There is some remark i should about the assumption I used in my previous post : putting 130 cells per LAC works in european networks (with a “european” call mix).

    In other countries (Africa, Middle East), it’s highly probable that a LAC should contain less cells, because the amount of paging is much higher. (a lot of fixed-to-MS calls, a lot of “beeping”, etc)

    Well, anyway, i’m just giving guide lines, you have to use them carefully and thoughtfully.


    Hi Pix,

    Having a LAC splitted in many BSC will lead to an important paging load in the BSCs. right ?

    What other bad influences it will have ?



    skippers, yes, in the end, it could lead to this situation of BSC paging processing overload. I mean, if you do it just once, i guess it’s alright. It should be monitored thanks to BSC counters (number of Paging Request incoming from MSC)

    there is no other bad effects, as far as i know.


    if i have 12 distrct and i want to give different LAC to each district and i want to keep all this sites in one BSC then what will be its impact


    Hi buddies,
    1-we have a Huawei BSC with 2 LAC and 5800 Erlang and 6 Siemens BSCs with 1500 erlang traffic per BSC.they worked nice.
    we swapped our MSC from ERICSSON to Huawei MX3000 MSC.
    but unfortunately we face to TCH_Assignment_failure = 2% in whole of Huawei sites in all of Huawei bsc.
    what is your advice?
    2-is it wise we divide huwaei bsc to 2 new bsc?!


    it is a trade off between CPU processig capacity for a)paging and b)Location updates. So, one of the CPUs may report overload if we hit the limits. I did never see an algorithm/tool for full calculations and it would also change with every new hardware release or software. Be happy, if 1 LA/BSC works fine. Recently introduced features such as “Precise Paging” may reduce the paging load within the LAC, if the algorithm can remember the last cell of the mobile.

    Rakesh Solanki

    What is the main effect when 1 LAC crosses 2 or 3 BSCs.


    i want to know what is the effect of LAI size in GSM Architecture.
    Suppose what will be the effect if LAI is Large and What will be the effect if LAI is small?

    Thomas MUNYANEZA

    Hi, I want to activate national roaming for some sites to be shared by two operators, and national roaming is activated at LAC level. Considering that the sites whereby i have to activate national roaming are very scattered and in different LACs, if create a LAC for every site (Island sites), what will be the negative impact in my network?

Viewing 13 posts - 1 through 13 (of 13 total)
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