Protected distribution system

A Protected distribution system (PDS) is a wireline or fiber-optics telecommunication system that includes terminals and adequate acoustical, electrical, electromagnetic, and physical safeguards to permit its use for the unencrypted transmission of classified information.

Note: A complete protected distribution system includes the subscriber and terminal equipment and the interconnecting lines. Deprecated synonym approved circuit.

Source: from Federal Standard 1037C and from the National Information Systems Security Glossary