iMessage and FaceTime Delay

Incoming iMessage and Facetime are not getting instantly when I am on DHCP Client Broad Band Service.

Internet Speed is Excellent. It is 40 MBPS

But outgoing iMessages and FaceTime are working instantly.

But When I use Mobile Data or DSL Broad Band then incoming iMessages and FaceTime also responding instantaneously.

Our service provider checked every thing and confirmed all ports are open. No issues from their end.

Is there anything I have to do specially in WiFi router.

What could be the wrong with DHCP Client Broad Band?

Madhu