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Awoffset and drop calls

Viewing 15 posts - 1 through 15 (of 16 total)
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  • #45038 Reply
    lucka
    Guest

    Hi!
    i am wonder if can explain me, how to manage this parametr AWOFFSET in relation to the high calldrop rate or just to suggest how to better use it.

    I have an Ericsson BSS and NSS.

    Thank you in advance!

    #45039 Reply
    Pix
    Guest

    Hi Lucka,

    Can you give the definition of this parameter AWOFFSET, because I guess I can help you but I can’t recognize the name of this parameter (different equipment’s vendor = different parameters names, but the parameters usage is still the same).

    — pix

    #45040 Reply
    lucka
    Guest

    Hi Pix,

    AWOFFSET is the “Assignment to Worse cell OFFSET”.

    In the Ericsson documentatio they write:
    ….”AWOFFSET is a signal strength offset parameter. It defines the maximum range of the signalstrength corridor between a congested serving cell and its neighbour, in where the neighbour cells are eligible as candidates for Assignment to Worse Cell. For example: The MS measures SS (serving cell) = -70, AWOFFSET = 15 allows assignment to neighbour with SS = -85 or stronger. The parameter is set per neighbour cell relation”

    I really appreciate your help!
    Regards
    Lucia

    #45041 Reply
    Pix
    Guest

    Ok, I understand now. In Alcatel’s system, it is not an offset but an absolute value (if neigbour SS > -85dBm, whichever the serving cell SS, then the neighbor is a possible candidate).

    Anyway, you can try to set this parameter to “0” on your problem cell, and check how it reacts. It means that when the Serving Cell is congested, the MS will go to a neighbor cell which has the same or better SS.

    Second thing : AWOFFSET relates to congestion in a cell, but not DIRECTLY to call drop rate. However, it might lead to a call drop in the neighbor cell because the MS was sent to a neighbor cell with a very low RXLEV (in case where : Serving cell – AWOFFSET = very low RXLEV)

    In consequence : check that your serving cell is congested AND the high call drops occur in the neighbor cell at busy hour only.

    If it is not the case, then you might have to suspect another problem (maybe it is just a coverage issue, or an interferene issue)

    #45042 Reply
    Optimizer
    Guest

    Hi Lucka,
    The reason of high call drop rate is due to the SD mean holding time, i-e lets say call gets SD from the serving cell and immedialty TCH assignment take places from neibor cell (depend on the AWOFFSET Value) due to congestion. But if the signal strength gets drop on the neigboring cell it will get back to SD of the serving and if by that time SD mean holding times gets expire the call will drop.

    #45043 Reply
    lucka
    Guest

    Hi optimizer,

    thanks for your reply. how does the “SD mean holding time” is calculated?

    For Pix: I´ll try to set up the AWOFFSET to 0 and look what happens.

    Best regards
    Lucia

    #45044 Reply
    pix
    Guest

    optimizer .. if the mobile is on the TCH of the neighbor cell, it will not try to go back on the SDCCH of the previous serving cell.
    It doesn’t work this way. A handover is SDCCH -> SDCCH or TCH –> TCH only.

    Luca : SDCCH MHT = SDCCH ERLANG / SDCCH ALLOCATION SUCCESS

    #45045 Reply
    Optimizer
    Guest

    Thanks Pix for the clarification. What would be the case in Call setup and incase of imediate assignement.

    #45046 Reply
    pix
    Guest

    the mobile is on the SDCCH of cell A, waiting for a TCH. The BSC is measuring that the cell A is congested, so it is looking for a TCH on a neighbor cell that meets the radio parameters conditions ( = acceptable RxLev AND enough free timeslots)

    BSC finds Cell B meets the requirements. Consequently the mobile sets-up the call on a TCH in cell B, and “succesfully” releases the SDCCH in cell A. That is not called a handover, but a Directed Retry (or Forced Directed Retry).

    Seconds later, the mobile is on TCH of cell B, but radio conditions are actually too bad, and it must handover to a better cell. BSC will look for a better cell. The better cell is found to be Cell A. The mobile does a HO from TCH of cell B to TCH of cell A. That is a Handover.

    #45047 Reply
    Vanderlay
    Guest

    Hi Pix,

    If the MS tries to go to the TCH of the Neighboring cell B from SDCCH of cell A, but due to bad radio conditions is unable to estabilish the connection then it will go back to the cell A SDCCH.
    “Unsuccessful Directed retry with reversion to old SDCCH” (T3124 expired (fixed to 320ms)). MS goes to the old SDCCH and reports HO Fail. So SDCCH is not released during that time. It is released only if Timer T8 expires or receives a message that TCH is allocated succesfully. This is the reason to have T8>T3124.
    Such problem could increase SDCCH MHT (check value of timer T8 in the BSC)

    #45048 Reply
    pix
    Guest

    Hi Vanderley,

    Interesting situation, I’ve never come across such a problem before. Thanks for the detailed explanation.

    I just found a few cells in my network that have that kind of high ROC (during DR), i’ll investigate them.

    #45049 Reply
    MAK
    Guest

    in our measurement tool which measures the QOS for the operator we found out in L3 messages that after call proceeding a successful HO is detected and that happened before the connection is established bet the MS and the BS and the measurement tool considered this as a blocked call..so how a successful HR can be done before a connection is established.

    #45050 Reply
    pix
    Guest

    call proceeding is a message that is sent on the TCH. It means your TCH is already established. Therefore a HO is already possible.

    I guess your QoS Tool should be fixed not to take this situation as a problem, if it is indeed what’s happening.

    #45051 Reply
    Da Architect
    Guest

    I just wanted to note that AW in ericsson behaves like Directed-Retry in Alcatel.

    #45052 Reply
    pix
    Guest

    What does it mean “AW” ?

Viewing 15 posts - 1 through 15 (of 16 total)
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