About firewalls and how they might affect your VoIP service.
A firewall is a system of hardware or software which serves as a primary layer of security for your organization’s network. Your firewall will filter any incoming and outgoing traffic through your network. Any untrusted or inappropriate traffic detected based on preconfigured settings will be immediately blocked and legitimate traffic will be allowed, thus keeping your organization’s network safe from unwanted threats and malicious activity.
Depending on the type of firewall, you may experience a loss in communication during your call. VoIP communication is a multi-step process to establish a call. If your firewall identifies any part of your call session as unrelated or untrusted, then situations where a one-way call may occur, or the phone call may never establish properly at all.