Overview

You noticed that calls to a particular MS Teams number made from Zoom phone do not complete. Calling from mobile works normally.

<supportagent>

Prerequisites

• Screenconnect access
• Hepic access
• TCPdump/Wireshark to collect/review SIP messages
• Knowledge of protocols and how to read and analyze SIP flow messages

</supportagent>

Solution

To start with troubleshooting, we will need fresh call samples. Reproduce the issue and open a ticket with Support, making sure to describe the issue and any symptoms you observe, and add at least two call samples in the following format:

• Calling From Number:
• Calling To Number:
• Date of call: dd/mm/yy
• Time of call: xx:xx am/pm (time zone)
• Trouble observed: Inbound or Outbound
• Description of the failing scenario

<supportagent>

Such issues are rare, and the impact of this type of case is medium. Once you have the details and call samples from the customer, proceed with the steps below.

1. In a Screenconnect VM use Hepic to search for the samples provided.
2. If you see any failures in SIP signaling, see where these come from (our SBC, AT&T, customer side) and reach out to the SaaS, AT&T, or the customer with the findings. If no failures are found, open a ticket with AT&T to verify what they are seeing on their end.

Known Cases

Issue with Microsoft

In one case encountered, there were no issues from the SBC side in the traces, and a ticket was opened with AT&T. Their finding was that the Called party PBX responded with the following:

SIP/2.0 500 Internal Server Error
SERVER: Microsoft.PSTNHub.SIPProxy v.2023.3.18.1 i.USEA.13.

This is an error from Microsoft, and the customer was advised to open a case with Microsoft providing the logs/traces and findings shared.

</supportagent>

Verification

Once the root cause is fixed, try to replicate the issue to confirm that it is no longer there.