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Call disconnection in GSM

Viewing 15 posts - 1 through 15 (of 19 total)
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  • #36263 Reply
    David W

    Hi all,

    I am interested in the tech. aspects of call disconnection over GSM networks.
    Is it defined in a standard, is it controlled by the BTS, is it configurable by the carriers?


    #36264 Reply

    Call disconnection over GSM network may happen due to radio link timeout, or handover failure, etc. What are you interested, for example the condition for call disconnection, or the process between MS and the network? Pls desribe your question in more specific scenario so that I can help you. You can refer to GSM 04.08 (RR connnection release procedure), 05.08 (radio subsystem link control), 03.09 (handover) for more information.


    #36265 Reply

    Hi all,

    I need to know the same thing.
    I have in fact, a call drop problem in Ericsson network.
    We have rehomed some sites from one BSC to a BSCX/TRC, and we face a lot of drop calls called “other reasons”
    ndlr: all neighboors and BSS parameters well defined.

    #36266 Reply


    What do you mean “rehomed some sites from one BSC to a BSCX/TRC”?

    Are you sure that all BSS parameters well defined? I think this is not easy matter.

    If you have a BSS parameter set for a BSC/BTS/Cell that has call drop problem, and/or a TEMS log file, I may try to investigate the problem.

    #36267 Reply
    David W.

    Hi Nguyen

    I am more interested in the conditions for call disconnections due to RF link performance. What are the condicitons in RF ( BER/FER level for some time, or others parameters, is it configurable and by whom)



    #36268 Reply

    On the layer 1 of the Air interface we have the parameter called RADIO-LINK-TIMEOUT. This parameter sets the threshold for the radio downlink failure on the SACCH (slow associated control channel). The channel should only be held for as long as a user could reasonably be expected to hold while experiencing loss of audio. After this, the user would assume the call had dropped, and hang up.

    This parameter is set from 4 – 64 SACCH frames, corresponding to 1.92 – 30.72 seconds (1 SACCH frame = 480ms). You can increase this parameter so that the MS will hold the channel longer in case of bad RF link performance.


    #36269 Reply


    I have experienced a peculiar problem in Siemens BSS. we have implemented half rate in one of our BSCs, it was found out that there was a increase in Drop call rate. The main reason for the increase in the drop call rate was the tint value settings in the BSC. when the tint value was set to zero(that is to say all the time slots are configured as half rate) the drop call rate came down. Can anybody explain how the tint value has a effect on the drop call rate?

    #36270 Reply

    Hi mostafa

    I faced the similar kind of problem where the dropped call was due to “other reasons”.
    I beleive that if call drop is happening due to “other reasons” it doesnt have anything to do with the BSS, and has some relation to the BSC. And i think if you test the TRA SNT’s in the BSCX/TRC you might find something interesting, like i did.

    Strictly refering to Ericsson System, even though the TRA’s were functioning fine the RP data for teh SNT was defined wrongly in my case. So see if you get a fault code, if u do let me know maybe i can help further.

    #36271 Reply

    Hi Sudhir ,
    the TINT parameter doesn’t have influence on call drop.
    TINT parameter define a threshold for the TCH occupation.
    Before assigning a channel the BSC determines the percentage of tchs not available for tch allocation
    Then the BSC in order to TINT value decide to assign TCH full or TCH Half


    #36272 Reply

    Hi Stefano,

    I totally agree with you. But i want to know whats the impact of this TINT value on the Time slots(TCH/TS) like for eg,(Letz take a scenario) if there are 8TCH available and the TINT value is set to 50% assuming 4 TS are occupied by 4 subscribers when the new subscriber tries to occupy the 5th TS which should be a Half rate TS based on the TINT value, in converting the 5th TS in to a half rate TS is it possible that the BSC drops the ongoing call in the rest of the TS.

    #36273 Reply

    Hi Sudhir

    here a description how the system assign the channel.

    Before assigning a channel (i.e. for Assignment or HO procedure) the BSC determines the percentage of TCHs not available for TCH allocation. This is done by
    dividing the total number of TCHs not available for calls (i.e. locked, failed or busy) divided by the total number of configured TCHs within the cell (TCH\F corresponds
    to 2 channel and TCH\H to 1).
    When the percentage of TCHs not available for TCH allocation has been determined two cases are possible:
    a) If the calculated percentage is equal or below the threshold entered by TINT the BSC assigns a full rate TCH no matter which speech version the requesting MS
    indicates as ‘preferred’ .
    b) If the calculated percentage is above the threshold entered by TINT the BSC assigns half rate TCH for all mobiles which indicate half rate version 1 as supported
    speech version, no matter which speech version the requesting MS indicates as ‘preferred’

    #36274 Reply

    Hi all,May I know what will be the proper cause value for a drop call issue but no announcement,only fast busy tone shall be heard.Based from the ITU, cause value
    27 is considered but there shall be an announcement heard.May I know what cause value aside from this will considered on a drop call issue?

    #36275 Reply

    Hi all

    I WAS IN CDMA TECH FOR 3 YEARS i am in NSN..I M NEW TO GSM our area calls going on in some of the sector…during drive test we observed that T3126 TIMER Expired..downlink is ok..but we are enable to MAKE A CALL..what could be the reason..

    #36276 Reply

    i have a problem with half rate trafic : drop call reason other half rate = 100%

    #36277 Reply

    Hi Stefano!
    Does HR don’t have influence on call drop?
    If not influence, why any time that i increase HR in BSC, CDR always increase, after i decrease HR, CDR decrease too? can you help me find the reason?

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