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Immediate assignment issue

Viewing 15 posts - 1 through 15 (of 21 total)
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  • #66316 Reply
    SFH
    Guest

    Guys advice please,
    after implementatin of new frequency plan on network, Sdcch assignment success rate of BSC has decreased from 98% to 60%.

    I tried to observe the problem, just the cells are degraded which has also SDCCH on TCH Trx. In a cell for a trial i ordered to delete SDCCH from TCH Trx. After deletion, SD ASGSR has increased from %50 to %99 on this cell which uses SDCCH just on BCCH TRx.

    Due to drivetest on below cases always ends with block call.
    MS2
    Immediate Assignment

    Time : 19:30:46.71
    Vendor Header
    L2 pseudo length : 12
    Skip indicator : 0
    Protocol discriminator : (6) Radio resources management messages
    Message type : 63
    Two-message assignment (TMA) : (0) No meaning
    Downlink assignment to mobile in packet idle mode : (0) No meaning
    TBF or dedicated mode (T/D) : (0) Assigns a dedicated mode resource
    Page mode : (0) Normal paging
    Channel Description
    Channel type : (8) SDCCH/8 + SACCH/C8 or CBCH (SDCCH/8)
    Subchannel : 6
    Timeslot number (TN) : 0
    Training sequence code (TSC) : 6
    Hopping RF channel : (1) RF Hopping Channel
    Mobile allocation index offset (MAIO) : 2
    Hopping sequence number (HSN) : 36

    and calls are successfull for below cases,
    MS2
    Immediate Assignment

    Time : 19:30:51.12
    Vendor Header
    L2 pseudo length : 11
    Skip indicator : 0
    Protocol discriminator : (6) Radio resources management messages
    Message type : 63
    Two-message assignment (TMA) : (0) No meaning
    Downlink assignment to mobile in packet idle mode : (0) No meaning
    TBF or dedicated mode (T/D) : (0) Assigns a dedicated mode resource
    Page mode : (0) Normal paging
    Channel Description
    Channel type : (8) SDCCH/8 + SACCH/C8 or CBCH (SDCCH/8)
    Subchannel : 3
    Timeslot number (TN) : 1
    Training sequence code (TSC) : 0
    Hopping RF channel : (0) Single RF Channel
    Absolute radio frequency channel number (ARFCN) : 528

    Vendor is NSN.
    Any idea to solve that problem?

    #66317 Reply
    Smart
    Guest

    Do u have FH?
    If yes move the SDCCH timeslots on your BCCH TRX.

    What do you changed on your new plan?

    #66318 Reply
    SFH
    Guest

    Yes we have FH, RF hopping.

    When i removed SD channels from TCH for 6 sites, all of them improved. When i add additional SD channel on BCCH TRX no degration.
    But they are for temporary solutions, i need permanent solution. I cant have more than 16 SD channel on BCCH TRx.

    We changed all frequencies and hopping MALs on new FP.

    #66319 Reply
    pix
    Guest

    hello sfh,

    could you describe exactly what’s happening when the MS is on the SDCCH which is hopping ?
    –> in the drivetest : what is the dl rxlev and dl rxqual, what is the BER ? what is the rxlev of the BCCH, just before the sdcch is allocated ? (is there a big diff between rxlev of the bcch and the rxlev of the sdcch ?

    –> in your qos tool : what is the main cause of sdcch DROP in those cells ? (we agree that the MS manages to get the SDCCH channel, so it is not a SDCCH Assignment Failure)
    –> in your qos tool : do you see many tch drops in those cells ? could you ensure that TCH are established on the “hopping” trx ? (= check that not all calls are located on the bcch trx)

    i’m also thinking about another kind of problem : the BSC that handles all those SDCCH timeslots. Are you sure that it is not overloaded ? Did you remap those sdcch on another bsc board, after the replanning ?

    please answer each question one by one, don’t miss anything ! ๐Ÿ™‚
    cheers
    pix

    #66320 Reply
    SFH
    Guest

    Hello pix,

    When ms is on SD which is on hopping TRX;
    Call initiation
    CM Service request
    Channel request is also OK,
    Than call attempt
    RR sent immediate assingment
    Than Block call occures(reason: no traffic channel assignment)

    But when ms is on SD which is on BCCH TRX;
    Everything is fine, classmark is fine, ciphering starts, finally call establishments..

    In drive test, both dl RxLev and Rxqual are OK. Anyway i ordered to dt team to test on dominant area of the serving cell and the test method is stationary for the problematic cells\sites.

    According to statistics, such low SD ASGSR cells has not high SD drops, no TCH drop problem. TCH assignment success rate is between %98-100 for problematic cells, is also OK.

    About SD overloading, when i remove sd channel from TCH TRX to BCCH TRX, sd asgsr is improving. I tried that for 9 cells and all of them improved.

    Cells are soft resetted, 1 cell hard resetted, no improvement. Just when i remove SD from hopping trx, there is improvement

    #66321 Reply
    Brother
    Guest

    check number of defined sdcch numbers maybe mistakenly reduced,

    are u using dynmical sdcch allocation u can check also this

    third thing comes to my mind maybe u defined layers for trx’s for traffic allocation u can dig these maybe all related maybe something else

    #66322 Reply
    SFH
    Guest

    SD channel numbers are OK, anyway the problem is not due to SD channel number, the problem is related with SD channels which on hopping TRXs.

    No we have, static SDs.

    There is no priority for allocation. MS can use SD from BCCH TRx or hopping TRx. Just the problem when immediate assingments on BCCH TRx everything is fine but when on hopping TRX we faces with block calls. And when i remove all SD channels from hopping TRXs, everything is going to be fine.

    #66323 Reply
    Rex
    Guest

    Hi SFH,
    What type of hopping you used before the implementation of new frequency plan? Since you don’t have drops that means your MAIO planning is OK. The next thing you might have check is multiplexing scheme on Abis. What multiplexing scheme you are using? If it is static then move to 64 statistic an see what happens (I dodn’t know for NSN if it’s same like in ALU, but, you know what I mean).
    Regards,
    Rex

    #66324 Reply
    Smart
    Guest

    If you are using hopping it is very important to set SD ts and PD ts on BCCH trx.

    If you set them on hopping trx you will have problems

    #66325 Reply
    pix
    Guest

    it’s great to see so many good ideas flying around !

    SFH > all your answers tend to prove that the problem is not “real”. There is no poor radio conditions, as TCH are fine, there is no SDCCH congestion, etc.

    have you checked the qos per trx ? your answer was not clear about this. Ensure that the sdcch ts is located on a trx that handles a lot of tch traffic as well, then look at the qos stats for this specific trx only.

    you should try to roll back to NH for few cells, see if it changes anything.

    cheers
    pix

    #66326 Reply
    Brother
    Guest

    One more thing,
    During implementation of new frequency plan, u have to lock cell define and then maybe trx’s will be shifted, and if trx has problem and was locked before or trx has problem but it was tch trx before and now shifted to bcch, this can create such a problem,

    so it is better to check trx quality and path balance stats as pix said

    #66327 Reply
    SFH
    Guest

    Thanks for your recommendations friends.

    The problem is solved, i have noticed that in imported XML all TSC values are wrong except BCCH TRx.

    Because of that SD channels which map on BCCH TRx were fine, but on hopping TRXs are degraded…

    Fyi.

    #66328 Reply
    Brother
    Guest

    kill them all…

    #66329 Reply
    pix
    Guest

    thanks for the update !

    now, that is something that’s impossible to diagnose ๐Ÿ™‚ even for the best rf engineers (like us !) ๐Ÿ˜€

    i didn’t even know you could change the TSC per TRX !! (well, in alu, it’s imposible)

    #66330 Reply
    Learner
    Guest

    Pix can you help me regarding this error ” terrestrial-circuit-already-allocated”. It d0 comes immiadately after Alert message from transcoder end.

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