Random Registration issues

[joshua@itstel.com]

Hoping someone else ran into this: I had a customer with 200 endpoints at a single location. One endpoint would not register. EVERY time I would reboot the router OR the ISP cable modem, a different endpoint would not register. I removed my router and connected the switches directly to the ISP modem and had the same issue. If I took the endpoint that didn't register to my office, it would register right away. Took it back to the customer, and wouldn't register. The customer was in the process of getting dedicated Internet, and when they did the problem went away.

Now I have a customer with 81 endpoints at a single location using cable modem having the same problem. Dedicated internet is not an option this time. These are my only two customers with more than 50 endpoints at one location and I had the problem at both.

Would the ISP limit somehow the number of endpoints? Would I need a static IP from the ISP? Both had Dynamic IP's. Would it be a NAT issue via port 5060 because of the quantity? Any insight or first hand experience would be helpful.