What Is a Protected Distribution System?
A Protected Distribution System (PDS) is a US government–defined wireline or fiber telecommunications system equipped with physical and electromagnetic safeguards sufficient to permit transmission of unencrypted classified national-security information. The governing authority is the Committee on National Security Systems (CNSS), and the current controlling standard is CNSSI No. 7003 (2015), which superseded the earlier NSTISSI No. 7003 (1996). Any program office or facility referencing PDS requirements should cite CNSSI No. 7003 as the operative document; NSTISSI No. 7003 is retained only as historical context.
The fundamental purpose of a PDS is to deter, detect, and make operationally difficult any unauthorized physical access to the transmission medium. Because the system itself provides the security assurance, encryption of the data in transit may be relaxed or eliminated — a significant operational advantage for high-throughput classified environments.
PDS Categories Under CNSSI No. 7003
CNSSI No. 7003 defines two principal categories of PDS:
- Hardened Distribution System: Employs robust physical construction — typically armored conduit, continuous-welded steel carrier, or equivalent — to make penetration physically difficult without leaving obvious evidence.
- Simple/Alarmed Carrier PDS: Relies on a combination of physical enclosure and an active alarm or monitoring system that continuously detects unauthorized access attempts, compensating for a lighter physical construction with real-time detection capability.
The Alarmed Carrier category is the focus of this guide and the primary use case for acoustic-sensing fiber technology deployed in modern secure facilities.
Acoustic-Sensing Fiber: How It Works
In an Alarmed Carrier PDS, specialized optical sensing fibers are routed within the conduit or carrier alongside the primary classified transmission medium. These sensing fibers exploit the physics of distributed acoustic sensing (DAS): mechanical perturbations — such as drilling, cutting, tapping, or even sustained pressure on the conduit — cause measurable changes in the backscatter pattern of light propagating through the fiber. An interrogator unit at one or both ends of the run continuously analyzes these optical signatures in real time.
The result is a system that can:
- Detect and localize acoustic events along the entire length of a conduit run without human patrol.
- Discriminate between background mechanical noise and anomalous intrusion signatures through signal processing and, increasingly, machine-learning classification.
- Generate immediate alerts — with approximate location — to a centralized monitoring console.
- Maintain a continuous, time-stamped audit log of all acoustic events for post-incident forensic review.
CyberSecure IPS: Alarmed Carrier PDS Solution
Heather Technologies partners with CyberSecure IPS to deliver an Alarmed Carrier PDS platform purpose-built for CNSSI No. 7003 compliance. The system integrates acoustic-sensing optical fibers within the conduit infrastructure and connects them to a centrally managed, continuously operating monitoring platform.
Key Capabilities
- Continuous Acoustic Monitoring: The sensing layer operates around the clock without gaps, eliminating the detection windows that periodic human inspection inherently creates.
- Automated PVI Support: CNSSI No. 7003 requires Periodic Visual Inspection (PVI) of PDS infrastructure at defined intervals. The CyberSecure IPS platform automates collection of the inspection and testing data necessary to document and demonstrate compliance, reducing administrative burden on security personnel.
- Centralized Management: A single management console provides visibility across all monitored segments, supports alert triage, and generates compliance reports aligned to CNSSI No. 7003 requirements.
- Scalable Architecture: The system is designed to scale from a single secure room to a multi-building classified campus, with sensing runs that can span substantial distances on a single interrogator deployment.
TEMPEST Relationship — An Important Distinction
PDS and TEMPEST are adjacent but legally and technically distinct security disciplines. TEMPEST addresses electromagnetic emanation security — controlling or shielding signals that could be intercepted remotely without physical access to the cable. A PDS addresses physical line protection: preventing or detecting hands-on access to the transmission medium. A facility may require both TEMPEST controls and a PDS, but satisfying one does not satisfy the other. Specifiers should evaluate both requirements independently against the applicable classified information system security authorization.
Deployment Considerations
| Factor | Consideration |
|---|---|
| Governing Standard | CNSSI No. 7003 (2015) — confirm current revision status with CNSS before program start |
| PDS Category Selection | Alarmed Carrier vs. Hardened — determined by facility construction, threat model, and authorizing official |
| Conduit & Carrier Design | Must meet CNSSI No. 7003 physical requirements; consult facility security officer (FSO) |
| Sensing Fiber Placement | Co-located within PDS conduit; interrogator placement at secure, access-controlled termination points |
| PVI Automation | Platform must generate documentation traceable to CNSSI No. 7003 inspection requirements |
| Integration | Alarm outputs typically integrated with Physical Security Information Management (PSIM) or security operations center (SOC) platforms |
Why Acoustic-Sensing Fiber Advances PDS Practice
Traditional Alarmed Carrier implementations relied on mechanical contact switches, pressure tapes, or optical-continuity loops that detect intrusion only at the point of complete breach. Acoustic-sensing DAS fiber advances this model by providing pre-breach detection: the act of drilling toward a conduit, cutting through an outer layer, or applying tools to fittings generates acoustic signatures that are captured and flagged before the classified transmission medium is exposed. This shifts the security posture from reactive to anticipatory, giving security personnel time to intervene before a compromise occurs.
For program managers, contracting officers, and facility security officers specifying classified infrastructure, an Alarmed Carrier PDS using acoustic-sensing fiber represents a defensible, continuously auditable technical control that directly supports the intent of CNSSI No. 7003 — and reduces long-term manpower requirements relative to purely inspection-based approaches. Contact Heather Technologies to discuss site survey, system design, and integration with your existing classified facility infrastructure.