First Post here

I have created this to try and help me hopefully could help others, anything i should add? how could i improve it? This isn't the main one i made a reddit copy , and some of the numbers changed,

https://docs.google.com/spreadsheets/d/15MepJBYKCq-3IVCw1p-KiRTmsXJGn77s/edit?usp=sharing&ouid=106038862253437246365&rtpof=true&sd=true

Please excuse the AI but its been trying to help me all day asked it to summarise my fault finding

[SUMMARY] SIP Inbound Calls Failing – Full Diagnostics Done, Need Expert Eyes

I’ve been troubleshooting a SIP handset that can make outbound calls, shows as registered, but inbound calls ring twice then go to voicemail. I’ve done extensive testing on both my UniFi network and a completely different 5G hotspot. The issue follows the SIP account, not the network.

Below is everything I’ve tested and what the packet captures show.

1. Environment

• SIP provider: Phonely
• SIP server: reg9.phonely.co.uk:5075
• Device: Wi‑Fi SIP phone (Yealink)
• Router: UniFi UDR
• Phone has a fixed LAN IP
• SIP ALG disabled
• Hardware Acceleration disabled
• Band steering, fast roaming, multicast blockers all disabled

2. Behaviour

• Outbound calls work perfectly
• Phone shows Registered
• Inbound calls ring twice then go to voicemail
• Same behaviour on:
  • Home UniFi network
  • 5G mobile hotspot (completely different ISP/router/NAT)

This already suggests the issue is not local.

3. Packet Capture Results (WAN interface)

A. No INVITE ever arrives during inbound call attempts

During multiple inbound call attempts, I captured traffic on the WAN interface (ppp0).
There is ZERO SIP INVITE traffic from the provider to my public IP.

No INVITE = the call is never delivered to me.

B. I do see SIP traffic in general

Example from capture:

Code

OPTIONS sip:613.third@reg9.phonely.co.uk:5075 SIP/2.0
SIP/2.0 404 Not Found

Provider responds 404 Not Found to OPTIONS for my SIP URI.
This is a huge red flag.

It means the provider’s SBC does not recognise the AOR/contact for this extension.

C. I do see BYE/200 OK for calls that DID connect

Example:

Code

BYE sip:613.third@192.168.0.228:5060 SIP/2.0
200 OK

So:

• My phone can receive SIP packets
• My phone responds correctly
• NAT is working
• Router is not blocking SIP

4. What this proves

Because:

• No INVITE ever reaches my router
• Provider sends 404 to OPTIONS
• Outbound works
• Registration shows OK
• Same issue on a completely different network
• BYE/200 OK works fine

The only logical conclusion is:

**The provider is not routing the INVITE to the correct contact.

This is a provider‑side issue.**

Likely causes:

1. Stale SIP contact binding on their SBC
2. Wrong IP/port stored for the extension
3. Extension mis‑provisioned (e.g., wrong AOR: 613 vs 613.third)
4. Cluster node mismatch (reg8/reg9 out of sync)
5. Account still bound to old office IP from earlier testing

5. Additional tests I ran

• Tried the phone on a 5G hotspot → same issue
• Disabled all UniFi SIP‑breaking features
• Confirmed phone sends REGISTER and OPTIONS
• Confirmed provider replies to BYE
• Confirmed no INVITE arrives during failing inbound calls
• Considering testing with another extension’s credentials to compare behaviour

6. What I need opinions on

Given the evidence:

• Does anyone see any scenario where this isn’t a provider‑side contact binding issue?
• Has anyone seen a SIP server return 404 Not Found to OPTIONS for a registered extension?
• Could the provider be caching an old contact from a previous network?
• Any edge cases I might have missed?

.

Thanks in advance — this one’s been a headache.