Защищённые телекоммуникационные системы правительственной связи США

Telecommunication system by the US Government
A protective distribution system (PDS), also called protected distribution system, is a US government term for 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. At one time these systems were called "approved circuits". A complete protected distribution system includes the subscriber and terminal equipment and the interconnecting lines.

The purpose of a PDS is to deter, detect and/or make difficult physical access to the communication lines carrying national security information. A specification called the National Security Telecommunications and Information Systems Security Instruction (NSTISSI) 7003 was issued in December 1996 by the Committee on National Security Systems. Approval authority, standards, and guidance for the design, installation, and maintenance for PDS are provided by NSTISSI 7003 to U. S. government departments and agencies and their contractors and vendors. This instruction describes the requirements for all PDS installations within the U. S. and for low and medium threat locations outside the U. S.
PDS is commonly used to protect SIPRNet and JWICS networks. The document superseded one numbered NASCI 4009 on Protected Distribution Systems, dated December 30, 1981, and part of a document called NACSEM 5203, that covered guidelines for facility design, using the designations "red" and "black". There are two types of PDS: hardened distribution systems and simple distribution systems.

Hardened distribution PDSs provide significant physical protection and can be implemented in three forms: hardened carrier PDSs, alarmed carrier PDSs and continuously viewed carrier PDSs.

In a hardened carrier PDS, the data cables are installed in a carrier constructed of electrical metallic tubing (EMT), ferrous conduit or pipe, or rigid sheet steel ducting. All of the connections in a Hardened Carrier System are permanently sealed completely around all surfaces with welds, epoxy or other such sealants. If the hardened carrier is buried under ground, to secure cables running between buildings for example, the carrier containing the cables is encased in concrete. With a hardened carrier system, detection is accomplished via human inspections that are required to be performed periodically. Therefore, hardened carriers are installed below ceilings or above flooring so they can be visually inspected to ensure that no intrusions have occurred. These periodic visual inspections (PVIs) occur at a frequency dependent upon the level of threat to the environment, the security classification of the data, and the access control to the area.