Why is RB433UAH client disconnect pptp with cisco?

Initial RB433UAH client can connect to cisco server but one period of time it disconnect to server a long time and may be connect again or can not connect. Whoever help me please…

check what the RouterOS log said, why disconnect happened …

It’log said terminating… -Keepalives time out. Did you explain to me about to log?

Check this:
http://wiki.mikrotik.com/wiki/Manual:Interface/PPTP#Server_configuration

It means that the server checked if the client is still connected, but received no responses, so it closed the connection because client was not responding.

I want to know Did it possible have session of connection still exit between RB433UAH and Cisco Router which their don’t know? or What is cause of disconnect? Help me please…

This is my project diagram

|------------------CDMA Signal-------------------|
RB433UAH Client---->PPTP Tunnel------>Cisco Router server-------->Dedicated-link-------->Cisco Router
|-------------------------------------->IPsec Tunnel----------------------------------------------------->|

Everthing OK but RB433UAH pptp Client alway disconnect to Cisco Router server. Whoever help me said to cause please… Thank a lot for your recommended