How does a Teams number stop completing calls without an alarm?
In Microsoft Teams, a call from the public network passes through the carrier’s trunk, an SBC and Microsoft’s voice service. An expired certificate, an SBC that stopped exchanging SIP OPTIONS, a codec with no match or an unassigned number takes the call down, and Teams keeps working between users.
The most common silent failures in Direct Routing:
- SBC certificate. The connection to Teams is SIP over TLS. A certificate that is expired, from an authority that is not accepted, or with a name that does not match the SBC takes the whole connection down.
- SIP OPTIONS. Teams sends SIP OPTIONS to the SBC and expects OPTIONS from the SBC. When they stop, because of a firewall, DNS or a blocked port, the SBC is treated as down and stops receiving calls.
- Codec and media. The SBC converts media between Teams and the carrier; a changed codec list ends in a 488 or in one-way audio.
- Number assignment. A number with no user, queue or auto attendant assigned is rejected.
- Carrier trunk. On the other side of the SBC, the trunk has the failures of any SIP trunk: registration, IP, channels.
Where do you look for each symptom?
In Direct Routing, the Teams admin center shows the health of each SBC, with the status of the TLS connection and the SIP OPTIONS, and the SBC’s own logs show both legs of the call. The table links each symptom to the most common code and the point to check.
| Symptom | SIP code or cause | Where to look |
|---|---|---|
| Every call stopped at the same time | TLS failure: expired or unaccepted certificate | SBC certificate validity and chain; SBC health in the admin center |
| SBC marked as inactive | SIP OPTIONS with no response | Firewall, DNS and TLS port between the SBC and Teams |
| Call rejected for one number | 404 Not Found or 403 Forbidden | Number assignment and voice routing policies |
| Rejected right after the INVITE | 488 Not Acceptable Here | Codecs on both legs of the SBC |
| Rejected at peak times | 503 with cause 34 | Carrier trunk channels, SBC sessions |
| One-way audio | NAT, media ports or media bypass | RTP ports on the firewall, SBC media settings |
What changes with Operator Connect?
With Operator Connect, the carrier provides the trunk and the SBC, and the numbers show up in the Teams admin center ready to assign. You do not handle certificates or OPTIONS, but you cannot see that equipment either. When the number fails, the test call’s evidence is what backs up the ticket.
Number assignment and voice policies stay on your side. Confirm the rest in your contract with the carrier.
What does a real test call catch that Teams does not show?
The Teams dashboard shows the connection between Teams and the SBC. It does not see a call the carrier failed to deliver to the SBC, and it does not know whether the auto attendant played the right greeting. A call placed from the outside, like a customer’s, crosses the whole path and returns the route’s SIP code.
It also checks whether audio flowed both ways and whether the measured voice quality, MOS-LQO, stayed above the agreed threshold.
How does Monitor monitor Teams telephony?
Monitor does not integrate with Microsoft Teams; it calls the numbers, so it works with any platform. 2N5 places real test calls at the agreed pace, retries each failure before alerting and delivers the incident with the SIP code and Q.850 cause of each call.
See the details in SIP trunk monitoring and, for service numbers, in 0800 and IVR monitoring.
Frequently asked questions
Does Monitor connect to my Microsoft 365 tenant?
No. Monitor does not integrate with Microsoft Teams or your SBC. 2N5 calls the numbers you choose, from its own platform, the way a customer does. That is why it works with Direct Routing, with Operator Connect and with any carrier.
Why does the SBC certificate take down every call?
In Direct Routing, the SBC and Teams talk SIP over TLS, and Teams only accepts the connection when the SBC certificate is valid, issued by an authority Microsoft accepts and matches the SBC's name. When it expires, the TLS connection fails and calls stop in both directions.
Isn't the Direct Routing health dashboard enough?
It shows whether the TLS connection and the SIP OPTIONS between Teams and the SBC are healthy, which is useful. But it does not show whether the carrier is delivering calls to the SBC, whether the number is assigned to the right person or queue, or whether audio flows both ways.
With Operator Connect, who fixes a failure?
The carrier that provides the service, because the SBC and the trunk are theirs. You cannot see that equipment, so the test call's evidence is what you take to the ticket: the time, the number called, and the SIP code and Q.850 cause of each attempt. Confirm the support channel in your contract.