lapd: adding support for ericsson's lapd dialect
Ericsson's RBS2111-BTS (and similar) implements a lapdm dialect which uses
a link establishment method that differs from the standard. While the BSC
is transmitting sabm frames on one specific timeslot, the BTS will
periodically scan through all timeslots to check for incoming sabm frames.
When the BTS detcts the sabm fames on one of the timeslots it will stay
there and continue to commence the link establishment.
The described procedure requires a slightly modified lapd profile, the t200
retransmission timeout has to be configured to exactly 300 msek. Otherwise
the link establishment will fail. Since the BTS will switch from timeslot
to timeslot most of the sabm frames will not be seen by the BTS, so the
maximum retransmission has to be increased. This patch suggests a maximum
retry count of 300, which is an educated guess and has worked fine during
our tests.
Change-Id: I892af57013d7ab4216e9e2d0873a69129aaeb8e5
2 files changed