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SDCCH Congestion

  • This topic has 5 replies, 1 voice, and was last updated 5 years ago by Moses.
Viewing 6 posts - 1 through 6 (of 6 total)
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  • #66455 Reply
    Adnan Afzal

    Hi Experts,

    I have one question. I have noted that there are few cells on which there are 5 SDCCH defined. The traffic is very low (around 2-3 Erl)but the cell continuously has SDCCH congestion.The cell has 3G cells collocated. If i see the Random Access dist. chart, majority of RACH attempts are due to RAOTHER (meaning location updates etc). My question is when the SD channels are well under utilized, then how come this congestion is appearing on the cells. Isn’t this congestion traffic based? If i increase the number of SD channels, the issue remains. I have tried to reset the timeslots but no improvement. However if i ask 3G guys to reduce the value of SSEARCHRAT to 0, the pingpong LUs are removed and also the congestion, but the SD traffic remains unchanged

    #66456 Reply


    i’ve seen such issues in ALU as well, cells with low “erlang” on sdcch are having congestion.
    There is a possibility that all LU are coming exactly at the same time (let’s say 100 LU Request every 10s)

    With only 5 SDCCH, the cell can answer 40 LU Req simultaneously. The 60 others are rejected due to congestion.
    In terms of erlang, those microscopic peaks of traffic are invisible.

    Of course, it’s difficult to confirm..

    One other assumption : the erlang are not properly counted. the erlang due to LU from 3G MS are not triggering the qos counters used for erlang computation.


    #66457 Reply


    I’m not an expert, but I just want to tell 1 case I know. In ALU there is SDD TS(dynamic SDCCH) which can be converted between RTCH/SDCCH. If your cell has 5 SDD and your TCH traffic is heavy then(most of your SDCCH is converted to RTCH) SDCCH congestion may occur. If this is the case then try to change some of your SDD to static SDCCH (SDC ‘physical’-8 SDCCH ‘logical’). It may help.
    If this is not your case I’m sorry – no idea.


    #66458 Reply

    Please check if any neighbouring site on another LAC fluctuates at that time as that would generate Location updated to this cell on an instance and causes congestion. check from their alarm logs, Also you can check from Max busy SDs to confirm if all SD timeslots are getting busy or due to some hardware issue your SDs can get stucked

    #66459 Reply

    I had one extreme case, location area border was on internal bus route , mobiles are open in the bus, 40 people assume 1/3 is with ur operator, 2,3 buses (50-60 mobiles) can block ur sd channels 🙂

    can be..

    #66460 Reply

    Pls, can some help me out with a simple and meaningful definition of SDCCH???


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