The phone rings but there is no audio when you're using a VPN or Sophos Connect.

Condition

You are able to place a call and the receiving phone rings but, no audio is heard.

Cause

This happens when the caller is unable to send data at the RTP stage of a SIP connection. This is shown in the image below where Alice is the caller and Boris is the recipient.

Remedy

  1. Go to Rules and policies > Firewall rules.
  2. Make sure you have configured a firewall rule for SIP.
  3. Make sure you select the recipient's network in Destination networks. Normally you will want to have this set to Any so that you can call any phone.