SOLVED Grandstream Phones won't answer

[ZIain]

I have just introduced some Grandstream WP820 wireless handsets to a tenant i have had for about 4 years. All their existing handsets are Yealink and Sangoma, this has been stable and working without issues for ages now. Adding the WP820's appeared to work fine when I set the first ones up, however when the tenant started using them I found out when one WP820 calls another the call is unable to be answered. When the WP820's call one of the desk phones there is no issue, and vice versa. The issue is only between the 820's.

Any ideas where the issue could be, or where to start troubleshooting?

Thanks.

 

[ZIain]

One other thing to note here, if I reject a call to the 820 from a desk phone, the desk phone gets the "busy here" message, however if I reject a call coming from another 820 then it carries on ringing on the handset that originates the call.

 

[ZIain]

What I've also noticed is that the registration info for the 820's doesn't have the contact, and that the LAN IP is actually their public IP address.

 

[ZIain]

I currently have 2 of the handsets with me for testing, and something else I've discovered is that sometimes handset 1 shows as registered on the handset itself, but not on the registrations page on FPBX. When it is in this state I am able to call handset 2 from handset 1, answer it and have a conversation. However handset 2 is not able to call handset 1 at all. After a period of time handset 1 will then show up in the registrations page and it's back to the previous situation where both handsets can call each other but neither is able to pick up the call.

 

[ZIain]

If I change the sip protocol to TCP on the handsets, then calls will are able to be answered, however that makes the registrations unstable, I mean sometimes the handset will become unregistered and won't re-register without manual input, and sometimes i will get multiple registrations for the same handset. Reverting back to UDP makes the registrations stable again, but goes back to not being able to pick up a ringing call.

 

[hfoster]

Sounds like NAT issues to me. You disabled SIP ALG on the firewall/router?

 

[ZIain]

Thank you @hfoster for making me check. That's exactly what it was. We disable SIP ALG by default so hadn't bothered to check. That'll teach me to never assume.

 

[hfoster]

It's a classic. 1 working phone = router rewriting everything SIP to 5060.