A couple of years ago we started seeing an increasing number of incoming “ghost” calls on our codecs. This only affected users who opened the SIP functionality on their devices to be compatible with SIP-based calling apps and WebRTC bridging. We cut some firmware to address this, by implementing a “blacklist” of common attributes of these calls. They got worse, and we couldn’t keep up with all the new robo-dialers, so we killed G.711 support so most of these calls would be rejected. Some still make it through and can tie up the codec for a short time until they get rejected. Now, we have a new app, and there will be more SIP users and it’s even more important to reject unwanted calls quickly. So here’s our third try…
First some background–The calls come in over the SIP channel integrated into our codecs. For convenience the codec will respond to any calls it gets from the Internet, not just a provider. This way you don’t have to worry about registering your SIP device and using a certain provider to dial in. You can make a direct call to your codec at it’s IP address without any proxies or other nonsense. This provides for more reliable connections.
The new approach is to integrate a “whitelist” of user agents from the calling apps we know folks use. If the incoming UA doesn’t match our list, the codec doesn’t respond. We’ve populated the whitelist with everything we know about, and users can add or subtract entries. It’s turned on by default but can be disabled by the user. This is available in firmware release 4.0p17 and above.
If you’re experiencing incoming ghost SIP connections, upgrade your codec firmware and you should be good!