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why only 8 time slots on a TRX?

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  • #53356 Reply

    hi Pix

    why there are only 8 time slots on a TRX ?
    why not greater than 8 or less than 8 ?

    #53357 Reply

    Its a trade off between capacity and quality.

    They tested 16 32 4 and 8

    8 is a balance of all benefits.

    If you have 16 TS on a TRX


    you will have similar experience as that of HR(half rate).

    And please note it has to be in power of 2, ie binary.


    #53358 Reply

    thnaks MKT

    can i find it somewhere specifically in docs, something u can suggest !


    #53359 Reply

    why in power of 2 only ?

    #53360 Reply

    Every thing is digital now
    and digital uses binary system.

    #53361 Reply

    hi MKT

    In voice we do the planning like :

    for a given GOS and the traffic in erlang , we can plan a site/sites with say (n) no. of trx ( traffic channels )

    Is there something like that in case of DATA ( GPRS/EDGE ) planning ??

    i.e , for a given throughput DL how can we plan the no. of radio timeslots to be given at a particular cell/site ….

    #53362 Reply

    hi pix

    need ur expert comment for the question below !

    #53363 Reply

    This planning of Data calls is already done when you are going to plan for TRX. Because ultimately TRX are responsible for Data calls as well.
    But the first priority is given Traffic channel and then to data channel.That’s why you well get less surfing speed while in peak hours and more at the time of night.

    There is no GOS for data calls.

    #53364 Reply


    the design of a site (number of TRX, number of sectors) based on voice traffic + data traffic is the right way to go.
    Unfortunately it is not easy to predict how much and when the GPRS is going to be used. It’s also difficult to estimate the amount of throughput required by the users in order for them to feel it’s “good”.

    For instance, for web surf, you don’t need so much throughput. But what you need is fast response time…

    an easy way is to always ensure the voice TCH are not using up all the timeslots (at least 2 or 3 are always available per cell, in order to provide “satisfying” GPRS access)

    QoS indicators can help you with that. Then you can perform drivetests in order to check out the overall data service “quality” of your operator. Do you “feel” that’s good enough ? Don’t forget, we’re talking about a very subjective matter here. You need to isolate some key performance results in order to qualify your network. Ping response time, throughput, reselection time, retransmissions, etc…

    #53365 Reply

    thanks pix

    ya , u r very correct that , it is a very subjective discussion.

    The QOS indicators are the RTT , Retransmissions , throughput/TBF .

    Pix, my RTT value is around 280ms for EDGE and 450 ms for GPRS( pinging at firewall ).

    average throughput/TBF DL/UL as 120kbps/25kbps EDGE
    average throughput/TBF DL/UL as 36kbps/6.1kbps GPRS

    i want to increase it further but how ??
    can u suggest me what can i do furhter at radio level?

    #53366 Reply

    TRX TS is basically depend upon TRX Signaling and which based on E1 so i we set 16 TS then one more E1 require

    #53367 Reply


    you can check interferences and coverage. That’s all you can do at radio level.

    Most probably, you need to increase your radio and abis capacities.

    Perform drive tests to see why your EDGE throughput is so low…
    regarding the RTT, that seems like a good value.. what RTT of subsequent pings ? (meaning, pings coming AFTER the first ping : the first ping takes a while usually.. the next pings are faster because they reuse the same TBF)

    #53368 Reply

    why a TRX has only 8 time slot ?

    #53369 Reply


    Good Re-question on the same thread.

    I’m sure PIX is working on it and will answer you in a while 🙂


    #53370 Reply

    optim -> :)) i wasn’t going to…. but since you ask…


    time is infinite, and when someone was asked to slice it into little slots.
    who asked ? probably a manager of some sort.
    anyway, this guy first decided to cut it into 0 slots. Dividing infinity by 0 was quite an impressive task, but yet it didn’t quite blow away its manager. Indeed, it didn’t comply with the requirements : it was nearly impossible (within the assigned budget) to apply half-rate to such slots.
    So he divided infinity by infinity itself, which is symbolized by the number “8”. By the end of the day GSM was born.
    But from the first experiment, a lonely timeless burst went rogue. It quickly evolved into CDMA, a parallel universe where timeslots are banned.

    I guess I should update wikipedia with this story.


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