Good evening, Shafar!
This very morning I has been working on the same problem for one of our MX BSCs. – enormous MC739 (Number of dropped calls due to remote transcoder failure) counter.
(as I see you also have a problem with MX BSC they must be twins I think :)))
From my experience – in 99,9% of cases the cause is faulty MT120 board. The question is how to find it (and the sooner the better :)) especially if you have a lot of Aterm (> 20).
You can get from NPO or RNO statistic for Aint-channels (in NPO this option is available only if you have working zone with less than 2000 cells) – particularly for that BSC for several hours. There are only 2 counters: C750 and C751.
C750 – TIME_A_CHANNEL_BUSY
C751 – NB_A_CHANNEL_ALLOC if my memory doesn’t trick me
C750/C751 is average duration of Aint channel occupation.
Normally it ought to be around 30 – 40 sec. Of course you see much grater range in your values, but be very careful – if you see some channels where during some hour successively this value is around 3-3,5 sec – you are lucky and you’ve found faulty link.
Than – define an Ater link and reset MT120. It’s not bad to shutdown traffic on it before of course :))
Sometimes it doesn’t help and you should to change MT120 but it happens – as I see in our network – seldom.