Ping Zyxel IpDslam which is in other subnet.

I'm out of ideas. Can't think of any thing else that can cause this. It might help checking the logs of the Zyxel.

What is the previous default route gateway 172.80.1.1 pointing to. Is it another router? the default route should point to the router that leads to the internet. But that probably is not related to your problem.

172.80.1.1 is an Ip address of the system which was connected to other end of Dslam through Rj45 cable. it is used to configure the Dsalm. It has the Windows server 2003.

If i ping to 172.80.1.1 is also same result ie Request timed out.

Can the Zyxel ping itself? can it ping 172.80.1.2 and 127.0.0.1

I did not understood your question - Can the Zyxel ping itself?

I can ping 172.80.1.2 $ 127.0.0.1 from 172.80.1.1(Pc connected to other end of Dslam).

OK, Then can you ping 192.168.1.1 and 192.168.1.4 from 172.80.1.1 ?

Sorry, forget about my previous question, this is not possible since you have NAT running.