"Ghost calls" is a term used to describe where calls don't function as expected. These issues can manifest in different ways but generally fall into three main categories:
- Ring Group issues where calls don't answer properly or continue ringing
- Phones that ring constantly from random numbers
- Calls that connect but have no audio
This article explains the causes and solutions for each type of ghost call to help you quickly troubleshoot and resolve these issues.
- Incoming calls to a ring group don't answer when picked up
- Phones continue to ring even after someone has answered
- Call appears to be active on one phone but still rings on others
This issue is almost always caused by the local router/firewall.
- The router is not managing VoIP sessions properly
- Aggressive firewall settings are interfering with SIP signalling
- NAT traversal issues preventing proper call handling
When a call comes in to a ring group, the VoIP platform sends signals to multiple endpoints simultaneously. If the router doesn't properly handle the subsequent signalling when one phone answers, the other phones may continue to ring, or the call might not properly connect despite being answered.
- Follow our router configuration guide Security and Firewalls
- Check and update router firmware to ensure it properly supports VoIP traffic
- Configure SIP ALG settings (usually this should be disabled)
- Open appropriate firewall ports for VoIP traffic
- Enable QoS (Quality of Service) to prioritise VoIP traffic
- Ensure proper NAT handling for SIP traffic
If you're using a consumer-grade router in a business environment, consider upgrading to a business-class router with proper VoIP support.
¶ Random Inbound Call Spam
- Phone rings constantly from unknown or random numbers
- Call logs show unusual international numbers or patterns
- Issues appear suddenly and stops, then comes back sporadically
This issue is especially common on Yealink and Grandstream phones. It occurs when malicious actors scan the internet for exposed VoIP devices.
- Adjust the local SIP port away from the default 5060
- For phones provisioned through our platform, contact our support team for assistance
- For self-managed phones, change this setting in the phone's web interface
Changing the SIP port is highly effective as most scanners only target the default ports. This simple change can immediately stop the problem in most cases.
- Calls connect and appear normal, but you can't hear the caller
- Caller can't hear you, but you can hear them (one-way audio)
- Neither party can hear each other despite call connecting
- Audio works for some calls but not others
This is primarily a firewall issue where:
- The router is blocking traffic
- Router is providing unusable data to the voice platform
- Follow our router configuration guide Security and Firewalls
- Ensure RTP ports are open (typically UDP 10000-20000)
- Disable SIP ALG/SIP transformations on the router (these often cause more problems than they solve)
- Configure consistent NAT handling for both signaling and media
- Test with a different network to isolate the issue