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IRAT PS Fail (Target Cell : 2G ALU )

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  • #69588

    Hi expert,

    For Huawei NW, we have high PS IRAT Fail, cause: Failed Outgoing UMTS-to-GSM PS Handovers due to UE Reselection Back to a UTRAN Cell

    Could anyone help about this topic, how to investigate this cause? what are the best values of 2G cell parameters? is there any timer which avoid ping pong 3g to 2g and 2g to 3g back?

    3g = Huawei
    2G = ALU

    Many thx


    hi styrax,

    Is there a way, with counters or traces, to know whether the failure occur during preparation phase on the 2G side, or during the radio phase, when the ue actually leaves the 3G and try to connect to the 2G ?

    FYI, in our network, we forbid the 3G2G PS IRAT : it was found to be better for customer to keep PS transfer in worst possible conditions, and drop / reconnect to 2G, rather than allow 3G2G PS Irat.
    The time for 3G2G PS irat is so slow, it makes sense to forbid it.



    Hi Pix,
    thx for ur response,

    concerning IRAT PS HO phases, PLZ could you confirm the following:
    – IRAT PS HO preparation phase include RELOCATION REQUIRED (RNC to CN) and RELOCATION COMMAND (CN to RNC)
    – IRAT PS HO completion phase include Iu-release command (CN to RNC) and Iu-release complete (CN to RNC)

    and btw 2 phases the message CELL CHANGE ORDER FROM UTRAN is sent to UE

    Could u PLZ provide details about IRAT PS fail causes, and during which HO procedure the fail occurs?

    Many thx



    yes , your split of the 2 phases is fine.

    in preparation phase, the error may come from:
    1/ congestion on 2G cell
    2/ misconfiguration of 2G cell in the 3G network
    3/ misconfiguration of handover parameters between 3G and 2G (for example, the 2G might be forced to reply to 3G with the message “I’m overloaded, don’t send any UE from 3G here !…)

    in execution phase:
    1/ real radio failure : the UE is in such a poor 3G radio that it can’t decode the relocation command
    2/ wrong BCCH/BSIC provided to the UE
    3/ wrong TBF information from the 2G (or whatever info the 2G sends to the 3G BSS regarding what’s waiting for the UE in the 2G cell)

    Further testing would be necessary : I never tried it myself, I’m just thinking out loud…


    Hi again,

    PLZ Pix, during preparation phase, does the CN (MSC or SGSN) ensure 2G resources before sending Handover from UTRAN for both cases PS & CS IRAT HO?

    I read before, that for IRAT PS HO, 2G resources will not be assigned before sending the handover from UTRAN message, is that true?

    and what is the difference btw Handover from UTRAN and cell change order message? and what is the difference with IRAT cell reselection procedure


Viewing 5 posts - 1 through 5 (of 5 total)
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