Step 1, make sure all 3 systems have the same software level.

Also check, I do not trust network admins, that the DHCP scope isn't messed up. IE, someone copes in and attaches a laptop or phone to the network and all of a sudden there is an IP conflict. If you are on a local switch and this is happening I would would be looking at that network really hard. Do what belevedere said but 95 out of 100 times it's always something network related. Pinging means nothing if routing is screwed up for everything else. Remember there are TWO IP addresses to check.

Thanks sir, for replying.
All systems are same software level,I think there will be some changes in 51-05 program, my setting for 3 systems are given below please suggest what modification should I do regarding this.
51-05-01-----5
51-05-02-----20
51-05-03-----5
51-05-04-----20
51-05-05-----10
51-05-06-----30
51-05-07-----40

They should be fine with default settings. You need to dive into that network. Wireshark etc...

Are you trying to run this site over a VPN?

Sir,
Client have their MPLS Line, remote location can be open any time from their network,but it will connect with primary after rebooting the remote location system by either soft reset or hard reset.Both systems are on same software version i.e. 10.60

In US we are using version 12.

The disconnect is caused by latency. The system automatically disconnects and reboots anytime it sees latency of over 200ms round trip. (failed heartbeat)

If the latency is over 240 ms round trip it will not reconnect.

I have had salesman sell the product expecting it to work over a VPN tunnel and it might connect but it will always go through phases where it will fail and reboot constantly. Netlink is only for customers who have their own fiber optic backbone. Even then latency will kill it.

If 51-06 is turned on and 02 is set to "reset when all packages are idle" the system will not reset if a phone is off hook. This includes a digital phone that might have the handset off the cradle. I had a customer who had a person at one of the remote sites who did that and the system would not reconnect. They had me drive 5 hours round trip to hang up the phone. At the time we thought there was an issue with the phone system.

If using 51-06 do not turn on 51-07 they conflict with each other.

Dear Sir,
As per your guidance, problem rectified.
Thanks all of you.