Like many businesses, we have a phone system that is VoIP-based. Occasionally, we will experience a no audio situation. Here is what I know about the problem:
- Almost always on a Monday morning or Tuesday after a holiday. (But not every week.)
- Affects all phones.
- Has been happening since 2020.
- Affects phones behind CODA-4582 and CGNM-2250 modems.
- Affects BC and Alberta.
- SIP over TCP/TLS or UDP works; RTP over UDP fails. Packet capture confirms the RTP traffic does not arrive to the VoIP service provider.
- Rebooting the Shaw modem solves the problem.
- Rebooting router, phones, switches does nothing.
- When the problem happens, multiple Shaw users in different cities report the same. (But not all.)
Other notes:
- I don't know if inbound audio would work. The service provider does not send RTP until the first RTP packet arrives. Since no RTP arrives to the service provider, no RTP is sent.
- CODA-4582 has a static IP and is in bridge mode. (Not sure about CGNM-2250.)
- This problem has been observed with multiple routers.
Still to test:
- Do devices using SIP over UDP have 2-way audio? (Edit: no they do not, same symptoms.)
- Are only specific UDP ports blocked and if so which ones?
- Does the problem correlate to a modem firmware upgrade? (Do I have access to find that out?)
- ???
Any other suggestions would be appreciated.
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