You use the Webex service?
See network requirements for Webex, Webex Meetings, and Webex Calling
Minimum Network Requirements
Network design and configuration has many variables, many of which can affect the performance and quality of Voice over IP (VOIP) service. For the Cloud Communications service to work in most network environments, there are a set of minimum requirements the customer network must meet below: https://carrier.webex.com/minimum-network-requirements/
Firewall Configuration Specifications
The firewall settings required for the Cloud Communications service to function properly are documented: https://carrier.webex.com/firewall-requirement-summary-2
- If you are deployed in the Cloud Communications server 1, please refer to the pages 15 to 20 of the guide.
- If you are deployed in the Cloud Communications server 2, please refer to the pages 24 to 27 of the guide.
