VOIP and CGNAT compatibility (Airband FTTP)

We have VOIP service with Port5060, through Airband FTTP, an openWRT router, a Cisco SPA122 ATA and Panasonic DECT base and phones.

Sometimes (say 1 in 5-10 calls) when the phone rings it correctly displays the callerID, we pick it up and there is nobody there. Hanging up and trying to ring back, there is no dial tone. Talking to the caller, the remote end just keeps ringing. I think we get a dial tone back when they give up ringing.

Port5060 are blaming Airband's CGNAT and say that there is no workaround.

I will raise a ticket with Airband, but I hold out zero hope of them actually doing anything.

Are there any workarounds or are we stuck with a copper line for eve? (Well until they disappear.

Thanks for any suggestions.

Sounds like either a SIP re-registration issue and possibly the one way audio is down to RTP stream being blocked or port timeouts somewhere in the food chain between your ATA and the provider.

On your side you may need to look into the SIP settings on the ATA to alter the SIP registration interval. Check any NAT traversal settings are enabled. You may possibly look at your firewall settings. I’m not au fait with your router but it may be worth tweaking SIP ALG setting to see if it makes any difference (better or worse!)

Some of these links may help in your understanding of what is going on and where the issues may lie:

https://phil.lavin.me.uk/2020/08/a-tale-of-voip-nat-...

Unfortunately a lot of the time it is something in the carrier network that kills stuff not always necessarily CGNAT. On my setups over the years I had decent performance with some wireless providers, namely Vodafone and EE (either on 4G or 5 connections which are all CGNAT). However I had no end of issues with Relish (now part of Three) and could never get decent VoIP service running over their net.

If you are reasonably techical you could packet sniff the network using wireshark to see what is happening with the UDP traffic related to your service.

I'd say its your VOIP providers issue as I have used VOIP behind CGNAT and have customers that do so with no issue.

Thanks
Dan

Easy way to test that is for the OP to open a free basic Sipgate account and enter the credentials on the ATA to test with.

In my experience it’s been the opposite. It’s usually the network rather than the VoIP provider that’s the issue.

SIP doesn't tend to like NAT very much in general although obviously there are workarounds.

Does Airband support IPv6? This may be the other solution, as everything should work with no NAT there.

I have a Cisco SPA 112 with the latest firmware which I recently updated. For my main service I have the "Register expires" set to 60 seconds, instead of the default of 3600 secs. There is also a "Auto Register When Failover:" not mentioned in the manual which I have now set to yes.

There is a Cisco forum for their ATAs.

Tim - I am also with Airband (but just their Wireless stuff) - and had awful problems with getting router to router VPN links working with their NAT because it was randmonly alternating between two different IP addresses while the connection was still active - even doing a keep alive ping did not stop this it would happily start with one external IP address and then at some point just flip to the other and later flip back etc.

I can't help but think this is a config issues somewhere in the Airband stuff but it plays havoc with anything that needs to connct back - in my case whenever the IP changed my VPN dropped and as remote end was using Dynamic DNS address to allow it would not then let me reconnect until the other end (which I did not control) refreshed or timed out it's DNS cache and looked up the actually IP again.

On the back of persistent moaning Airband gave me a static address. It might be worth checking if your address is also dong this - I setup a powerShell loop sending:

(Invoke-WebRequest -UseBasicParsing ifconfig.me/ip).Content.Trim()

to get my address

Change network provider (they sound utterly rubbish. Life’s too short). Keep the VoIP provider.

Thanks you for all your replies, Very useful.

The current situation is that searching the openWRT forum I found a post about similar symptoms and their fix was to install nf-natfiler-extra kernel modules, I have now done this, it remins to be seen if it has fixed the problem.

Port5060 have come back saying that VOIP "should" work through the double NAT of my router and CGNAT, but it is not guaranteed. They have suggested as a test connecting the SPA122 directly to Airband PPoE feed, this would show if the problem is my router or CGNAT.

Thanks for the links , I may well resort to studying and understanding the protocol and using tcpdump on the router.

If only there was a choice.

Unfortunately Faster Worcestershire awarded the contrct to install FTTP here to Airband so they have a monopoly.

Adsl is around 2Mbps, in the house there is almost no mobile signal, but up at roof aerial height O can get a Three signal around 20Mbps, I lived with that for 18months and that is still an option.

My FTTP connection was paid for by a Gigabit voucher, so I am committed to Airband for 12 months.

I suspect that their business plan is to make their profit from the grants and vouchers for intalling FTTP, they are not interested in running as an ISP.

Another issue I have with them is that although speed tests come in around 200Mbps and pings to 8.8.8.8 in the 7-8mS I get frequent iPlayer issues, buffering, "something has gone wrong" or just being kicked out of iplayer back to live TV.