ROUTER R6080 CONNECTIVITY PROBLEM

I am using the router for more than two years.

I used to make whatsapp video call to canada (from India) using the wifi.

Since last three months or so whenever I am calling the call is hanging with message 

" Poor network connection "

But at this time when I am trying through some other router of the same ISP the call is getting through.

I have reset the router settings three/four times but same problem continues.

Can anybody help me in resolving the issue.