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Ghost calls

What are ghost calls?

Section titled “What are ghost calls?”

Customers often receive “ghost” calls, where there is no one on the other side and no record shows in the PBX call history.

This is typically SPIT — Spam over Internet Telephony. Malicious individuals use a SIP dialler to search for IP addresses that respond to a SIP INVITE. Most SIP phones on default settings respond to any INVITE, which tells the attacker your device is there and causes it to ring.

How do I know if I’m getting ghost calls?

Section titled “How do I know if I’m getting ghost calls?”

Review the PBX call history. If there is no log entry for the call, it is likely coming from a scanner rather than through our switch.

How can I prevent ghost calls?

Section titled “How can I prevent ghost calls?”

  1. Disable IP calls. Certain devices let you disable IP calling altogether. Check your device’s manual to see whether yours can.

  2. Only permit calls from our SIP proxy. This is device specific. In device settings, look for something like Accept Incoming from SIP Proxy Only and make sure it is checked.

    BrandGuide
    GrandstreamGhost calls on Grandstream phones
    YealinkGhost calls on the Yealink T48G

  3. Change the device’s default SIP port. Use something other than 5060.

  4. Block SIP packets from unknown senders. From your router or firewall, block inbound SIP packets except those originating from our SIP server and proxy.

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