tree 384aee29441ed73952a29d6729e51db0bed152d5
parent 22ce59826a77bf02f10773d16463a3896874c72a
author Harald Welte <laforge@gnumonks.org> 1371816378 +0200
committer Harald Welte <laforge@gnumonks.org> 1371816378 +0200

GPRS LLC: Add non-standard method of sequence number recovery

In some situations (like MS reboot without prior DETACH or SGSN reboot
without prior MS detach), the LLC sequence numbers for UI mode could
be different on both sides.

The LLC spec unfortunately doesn't permit us to send something like a
FRMR in this case, but instructs us to silently discard the frame.  At
that time the remote LLC entity will re-transmit the frame with the same
seqeunce number over and over again, which we will drop again and again.

The mthod used now will keep track of the last received UI sequence
number.  If that number is retransmitted for three times in a row, then
we accept this sequence number and recover from that point on.