CUNA and other organizations provided feedback to a communications task force Wednesday regarding the use of an enhanced signaling protocol (SIP Code) for voice service providers to notify callers a voice service provider has blocked their call.

The Federal Communications Commission (FCC) permitted SIP Code 603 to be used to temporarily satisfy this requirement in a December 2021 order. However, SIP Code 603 was originally designed to signal the call had been declined by the recipient, and CUNA has expressed concerns that the use of SIP Code 603 would not differentiate between calls declined and calls blocked.

An enhanced version currently under development–SIP Code 603+—would include header information indicating a voice service provider has blocked the call.

CUNA and the organizations raised several technical specifications important to callers when receiving a call blocked notification, noting the standards for SIP Code 603+ must:

• Utilize a uniform, standard word or phrase to indicate that the call has been blocked.
• Enable the code to be read using automated, machine-readable technology.
• Make it clear that a 603+ Code without a reason header signifies the called party has declined the call, and the code should not be used for any other purpose.
• Include, in standardized formats, the name and contact information for the blocking entity in the reason header.
• Address, to the extent practicable, the transmission of the 603+ Code across international boundaries
• Address which entity should receive notification where a third party initiates the call on behalf of a customer
• Consider cost of deployment and implementation by small carriers and both large and small enterprise callers.
• Ensure that callers’ calling applications are able to obtain the header on the 603+ Code.