Help with mbus sq numbering

[KarlisFreibergs]

I develope scurity aplication on AVR microcontroller and use
nokia 5110
trough mbus,im sucessfully send sms,call and work with
memory,
but when im use many commands one after one, nokia many
times
not respond vith ACK and ignore commands,or ignore my ACK's
and 
send all 3 packets,and this situation depends on sequence
numbers
that i use.The question is how to correctly nuber packets on
MBUS.