Dropping LLC frames due the TBF destruction

Andreas Eversberg andreas at eversberg.eu
Thu Nov 7 07:35:49 UTC 2013

(just ignore my last mail. somehow i hit the wrong key...)

hi holger, hi harald,

i looked at the TS 08.18. the LLC-DISCARDED.ind message does not contain
any reference to the frame(s) that has been discarded, so SGSN cannot
resend specific frames that are dropped. also a resend does not seem to
be specified. it is task of the PCU to be sure to deliver LLC frame.

during a downlink TBF, lost downlink blocks are resent by the RLC/MAC
protocol, but assignment is not. (at least not correctly)

here is my suggestion: if assignment fails, the PCU should resend
downlink TBF assignment several times. the number of retries should be a
config option. it may happen that the assignment on PACCH fails, while
the MS is in packet transmode. if the MS switches back to packet idle
mode in the meantime, the retry must be performed on AGCH. it may also
happen that the assignment on AGCH fails because the MS is establishing
an uplink TBF. if this happens, the retry must be performed on PACCH. if
the number of maximum retries is reached, the LLC frame (or list of)
should be discarded and the an LLC-DISCARDED.ind message should be sent
to SGSN.



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