WANs used which protocol developed by the Consultative Committee for International Telephone and Telegraph.

X.25 is a standard protocol suite developed by the Consultative Committee for International Telephone and Telegraph (CCITT), now known as ITU-T. It is one of the earliest protocols used for WAN communications, enabling reliable data transfer across public networks using packet switching.

XA.10 (B), CXA 1.23 (C), and X.20 (D) are not recognized standards for WAN protocols.