Ghost Calls

A ghost call is an incoming phone call with no one on the other end, usually from a random number, and occurring persistently. Ghost calls are unfortunately a well-known problem in the telephone industry. To protect your network from ghost calls, it’s important to make sure the firmware on your phones are up-to-date.

Ghost calls generally occur due to neglected auto-dialers from telemarketers, or hackers looking for networks to exploit. These hackers perform a large series of automated port scans on IP addresses across the internet to find vulnerable systems. Luckily there are a number of ways you can avoid being targeted.

Here are some ways to prevent ghost calls.

Block peer-to-peer IP calls

IP devices can call each other directly without using a server by sending calls directly to each other’s IP addresses, also known as peer-to-peer IP telephony. Unfortunately, this also opens up vulnerability for ghost calls. Some IP phones can disable direct IP calls, and only allow calls coming directly from Telzio’s server to your device.

Disabling direct IP calls on your device is the best way to stop ghost calls. 

Check your phone’s manual to see if your device can disable direct IP calls. Here are a couple of examples on how to disable direct IP calls:

Grandstream GXP2200

Advanced Settings – Call Features – Disable Direct IP Calls

Grandstream GXP2160

Accounts – Account 1 – SIP Settings – Security Settings – Accept Incoming SIP from Proxy Only

Use a firewall

Some firewalls are able to filter port scans from legitimate traffic. Check the manual for your router/firewall for instructions, or contact your internet provider for assistance.

Change your IP address

If you don’t have requirements to maintain a static IP address, you can ask your internet provider to assign you a new IP address. This may not be a permanent solution to eliminating ghost calls, but it can help to start.

Change the local SIP port on your phone

Changing the local SIP port on your phone will make it more difficult for hackers to guess their way into your device.

Here are a few examples on how to change the local SIP port:

Grandstream GXP2200

Account – Account 1 – SIP Settings – Local SIP Port

Grandstream GXP2160

Accounts – Accounts 1 – SIP Settings – Basic Settings – Local SIP Port

Cisco SPA303

Ext 1 – SIP Settings – SIP Port