The protocol was created to address the problem of call spoofing --calls that claim to come from a number or network, but they don't. SHAKEN/STIR works by the network operator where the call has originated "signining" the call using a certificate. The telecom operator on the receiving end of the call can verify it came from the network the call claims it originated by looking at its certificate and making a few cryptographic checks. Work on the SHAKEN/STIR protocol has been underway for a while, and until now, several telecom operators have tested it already, but with calls inside their respective networks, where they could verify that everything was working as intended and calls were getting signed correctly when made, and verified the right way when received. "The calls were successfully authenticated and verified using the SHAKEN/STIR protocol - believed to be an industry first for calls between separate providers," the US telco said. Telcos will be able to mark calls that not have been SHAKEN/STIR-signed as suspicious and consumer will be able to act on these warnings and turn down calls.