Silent Network Authentication (SNA) is a form of secure consumer authentication that protects end-users, accounts, and transactions without requiring user input, using direct carrier connections to verify possession of a phone number in the background. It's built on top of standardized GSM authentication systems used by carriers to authenticate mobile phone calls and data sessions, providing high assurance for each verified phone number. SNA is immune to social engineering and offers a frictionless experience, but its limitations include requiring users to be on cellular-connected devices, additional carrier approvals, limited availability in certain countries, and handling of dual SIM cards and data residency requirements.