modem disconnects shortly after PPPD connect...

After my modem dialing and pppd building in short time,
modem disconnets automatically.
What’s going on?

http://qdn.qnx.com/support/bok/solution.qnx?10101
This linked shows the same problem as me that many people reported to QNX,
but there isn’t any answer i could found…
Could someone dissolved the problem help me please??
THX a lot!!