While you cannot say for certain that a particular call is coming from a robot, being a major network you can make a very good guess. E.g. when the same origin hits every number with a caller ID in that number's exchange just block that origin from your network. If there is a legitimate reason for this - they will contact you immediately and sort it out. Bonus point - spammers will hit the competitors networks with more bandwidth and force even more people to consider switching.
The current situation is the one, which requires cooperation of the whole industry, actually. It's a prisoner's dilemma in the sense that the first one to implement anti-spam will gain a temporary advantage but eventually everyone will have to implement it and keep up with the spammers who will be finding new ways to circumvent these measures. As it stands now - nobody gains advantage and nobody has to spend money on anti-spam and lose revenue from spam at the same time. As little as it is, taking your $70 and $0.05 from spammers is a lot better than taking your $70 and zero from spammers.
There is no real concept of "origin". Unless you're the direct upstream carrier of the originator of the robocalls, the robocalls will be diluted with legitimate calls in such a way no single inbound carrier stands out.
I see, are there second layer provides agregating multiple VoIP retailers? I thought VoIP route directly to the big telcos networks. But even in this case - just drop the whole 2nd layer provider and they will quickly deal with their spammer clients.
Big carriers* often route directly, but even then, it's not guaranteed (they could use a third-party or even a competitor as a fallback in case their own interconnect goes down), and to be fair, big carriers (Twilio, etc) are decent at fighting abuse - it's not them we need to worry about.
Small & shady carriers are where the problem is, and those often just resell capacity from bigger carriers (some of which in turn resell even bigger carriers), or sometimes even resell illegal "black" or "grey" routes as they're called, could even be compromised servers from legitimate customers of big carriers.
In the end this entanglement mixes legitimate calls with malicious ones by the time they reach the destination (final) carrier, making it impossible for them to drop malicious calls without impacting a lot of legitimate usage.
*I avoid saying VoIP retailers because it doesn't really mean anything; carriers often allow you to use different interconnects, and VoIP is just one of many.
>In the end this entanglement mixes legitimate calls with malicious ones by the time they reach the destination (final) carrier, making it impossible for them to drop malicious calls without impacting a lot of legitimate usage.
No, I did not say "drop calls", I said drop the source. If Twilio got blocked on T-Mobile it would found which re-seller is responsible in no time. If it was their hacked server - they, again, would have found it and patched. It's no different from e-mail spam in early 2000s - all e-mail from a server sending spam would have been blocked, including legitimate e-mail.
The current situation is the one, which requires cooperation of the whole industry, actually. It's a prisoner's dilemma in the sense that the first one to implement anti-spam will gain a temporary advantage but eventually everyone will have to implement it and keep up with the spammers who will be finding new ways to circumvent these measures. As it stands now - nobody gains advantage and nobody has to spend money on anti-spam and lose revenue from spam at the same time. As little as it is, taking your $70 and $0.05 from spammers is a lot better than taking your $70 and zero from spammers.