1. GNSS Vulnerabilities Mitigation for Timing Applications
GNSS Protection 9 Layer Model
GNSS Vulnerabilities Mitigation for Timing Applications
Omer Sharar – Focus Telecom

2. GNSS Vulnerabilities - Jamming
Common GNSS jammers available online:
Critical Infrastructures, both Commercial & Defense, are totally GPS dependent
A good, Rubidium based atomic clock (like the MAC) helps maintain good holdover which is a great short term solution for jamming
BUT even the greatest Rb based timing system will not comply with today’s stringent timing requirements for a long time without GPS
DIY GPS jammer diagram:

3. GNSS Vulnerabilities- Spoofing
A spoofing attack tricks the receiver with false position / time
Could cause SEVERE damage for any network

4. Introducing: The GNSS Protection 9-Layer Model
The Front-End Layer: GPSdome front-end protection
APTS
PTP
The Mask Layer: Configurable Antenna Elevation Mask
The Cutoff Layer: External GPS Switch
The Firewall Layer: BlueSky GPS Firewall
The Receiver Layer: GNSS Multiple constellation
The Management Layer: TimePictra
The Network Layer: PTP with APTS
The Holdover Layer: ePRTC / Rb / OCXO 1
The Client Layer: DomainTime II 2 3 4 5 6 7 8 9

5. Layer 1: The Front-end Layer – GPSdome
Standalone, retrofit, dual antenna module
Applies CRPA, null steering algorithm
Rejects disruptions by nullifying their energy
Compatible with any GPS system
Introduces minimal latency to RF signal (50ns)
Deterministic fixed delay
Qualified by INPL

6. Layer 2: The Mask Layer
A SW configurable option of Microsemi timing systems receivers
Allows for rejection of lower-elevation satellites
Allows for protection from multi-path
Allows for rejection of spoofing attempts

7. Layer 3: The Cutoff Layer – Focus Telecom’s GPS Switch
An external, standalone module which cuts off the GNSS feed to the receiver and the DC back to the antenna
Minimizes exposure to GNSS
With 2 modes of operation:
Remote controlled: remotely turned on or off from control center
Preprogrammed: Disconnected GPS for X hours/days, then connect for Y hours/days

8. Layer 4: The Firewall Layer – Microsemi’s BlueSky GPS Firewall
Microsemi’s BlueSky GPS FW assures correct GPS data and autonomous time scale
Analyzes GPS data and flags anomalies according to IS-GPS-200H with user configurable abilities
When anomaly is flagged, GNSS is cut off and hardened GPS data is synthesized allowing the receiver to continue working uninterrupted
Optional external input from atomic standard enables extended holdover and enhanced detection capabilities
Validated GNSS data
“Hardened” GPS data

9. Layer 5: The Receiving Layer
A multiple-constellation GNSS receiver receives satellites from more than a single constellation
Allows for more satellites in view
Allows for sanity checks of constellation
Avoids dependency on US owned GPS system
More resistant to narrow-band jamming

10. Layer 6: The Management Layer – Microsemi’s TimePictra NMS
Monitor all sync elements in the network
Allows for comparison between multiple units geographically apart
Allows to track anomalies e.g. shifting position in stationary units
Allows for statistical data of satellite reception trends
Provides gauges on time quality the network provides (PTP)

11. Layer 7: The Holdover Layer – From OCXOs to ePRTC
Optimal time HO is achieved Microsemi’s ePRTC (ITU-T G and G.811.1)
Better than PRTC (100ns) to UTC for over 2 weeks without GPS
Microsemi’s Rb technology (MAC and XPRO) provides for optimal local holdover (<1uS and 24 hours)
Patented temperature-compensation technology allows for <25uS holdover with an OCXO

12. Layer 8: The Network Layer – PTP with APTS
Backup network edge timing from Core
IEEE 1588 PTP with APTS (Assisted Partial Timing Support) allows for accurate source of time
Implementation of Microsemi’s APTS at the network edge compensates for network asymmetry of 30 different paths from the Core
When GNSS is not available, a fallback on PTP will not compromise accuracy at the network edge

13. Layer 9: The Client Layer – Microsemi’s DomainTime II
Time Management system (for IT NTP/PTP networks)
Monitors time all the way to the client
Implemented on the DC, DTII SW could receive time from multiple sources and compare them for inconsistencies
With auditing capabilities, the accuracy of each client could be measured, recorded and analyzed