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Regarding T200 and N200 values.

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  • #47417

    Hi! All,

    Thank you in advance. I want to know about T200 and N200. Let I set T200=235.38 ms*2 (i.e, 470.76 ms) and N=3 for SDCCH (SAPI0).

    Does T200 restart once in every Control channel multiframe irrespective of its value?


    If T200 expires only after a set value, then the messages will be repeated 4 times only or 8 times as indicated my N200 values??



    Hi NK,
    Please see next explanation from documentation (I think it could be much more clear to you):Principle: When the BTS transmits a DL layer-2 frame on the air (e.g.
    an I-frame with an embedded layer 3 message) the BTS starts the
    timer T200 and waits for the acknowledgement frame from the MS.
    The acknowledgement frame can be another I-frame sent by the MS
    in the UL (if the MS has to transmit a layer-3 DTAP message
    anyway) as well as RECEIVE READY (RR) if there is nothing else to
    be transmitted on layer 3. If the acknowledgement from the MS is not
    received within T200 the transmission of the layer 2 frame is
    repeated and T200 restarted. The total number of repetitions is
    restricted to N200, a fixed value for the BTS side specified by GSM
    which depends on the control channel types:
    N200(SDCCH)=23, N200(SACCH)=5,
    N200(FACCH/FR)=34, N200(FACCH/HR)=29
    If T200 expires after the last layer 2 frame repetition the BTS sends
    an ERROR INDICATION with cause ‘T200 expired N200+1 times’
    (followed by a RELEASE INDICATION) message to the BSC, which
    releases the associated resources.

    Br Tomar


    so it follows the typical mechanism of timer / ack / retries / error.

    pankaj kalyani

    hi all,
    can u tell me abt T200

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