Information About GNSS
Industrial automation and control, utilities, and military networks require large numbers of devices in their networks to have an accurate and synchronized view of time. The IR8340 timing module has a built-in Global Navigation Satellite System (GNSS) receiver that enables the router to determine its own location and get an accurate time from a satellite constellation. GNSS capability simplifies network synchronization planning and provides flexibility and resilience in resolving network synchronization issues in a hierarchical network.
GNSS Hardware
The IR8340 timing module uses a GNSS receiver with precise frequency and phase outputs for the host system. When connected to an external GNSS antenna, the receiver contains all the circuitry necessary to automatically acquire GNSS satellite signals, track up to 32 GNSS satellites, and compute location, speed, heading, and time. It provides an accurate one pulse-per-second (PPS) and stable 10 MHz frequency output. For more information, see GNSS Signaling.
 Note |
You are recommended to choose GPS LRM-400 cable for GNSS so that you can check all GNSS alarms. For a list of supported antennas and cables, see the Cisco Catalyst IR8340 Rugged Series Router Harware Installation Guide. |
The GNSS chip supports the following frequency bands:
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AUTO—GPS + QZSS + GLONASS (default)
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GPS
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GLONASS
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BeiDou
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Galileo
Software
The GNSS feature supports the following functions:
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Time Mode—A special receiver mode where the position of the receiver is known and fixed, and only the time is calculated using all available satellites.
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Survey-in—The procedure that is carried out prior to using Time Mode. It determines a stationary receiver's position by building a weighted mean of all valid 3D position solutions. The receiver computes the average position over an extended time period until a predefined standard deviation has been reached and the minimum observation time has passed by. Afterwards the receiver will be automatically set to fixed mode and the timing features will be activated.
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Survey-in and fixed-position navigation reduce timing jitter, even at low signal levels, and enable synchronization to be maintained with as few as one single satellite in view.
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Time pulse accuracy—Clear sky: 20 ns | Indoor: 500 ns.
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Configures the GNSS receiver.
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After the receiver has gained lock, software performs the following functions once per second:
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Reads the new time/date.
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Reads the corresponding PPS timestamp from the hardware.
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Feeds time/date and PPS timestamp into the Time Services SW Virtual Clock/Servo for GNSS.
The GNSS SW Virtual Clock time can then be used to drive PTP output.
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You can use the constellation CLI to choose between these constellations. When a constellation is changed, survey-in process is restarted to lock to a new constellation. For more information, see Configuring the Satellite Constellation for GNSS.
Default TOD format is ubx and out 1PPS can get when GNSS is locked (for example, PRTC mode).
Frequency 1hz: the following commands are required to enable to get locked:
Router(config)# network-clock synchronization automatic
Router(config)# network-clock synchronization mode QL-enabled
Router(config)# network-clock quality-level rx QL-PRC External R0 1hz
Router(config)# network-clock input-source 1 External R0 1hz
Router(config)# network-clock wait-to-restore 10 global
GNSS Signaling
There are two stages in the process for the GNSS receiver to acquire satellites and provide timing signals to the host system:
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Self-Survey Mode: On reset, the GNSS receiver comes up in self-survey mode and attempts to lock on to a minimum of four different satellites to obtain a 3-D fix on its current position. It computes nearly 2000 different positions for these satellites, which takes about 35 minutes. Also during this stage, the GNSS receiver is able to generate accurate timing signals and achieve “Normal (Locked to GPS)” state. Note that the timing signal obtained during self-survey mode can be off by 20 seconds; therefore, Cisco IOS collects PPS only during OD mode.
After the self-survey is complete, the results are saved to the GNSS receiver flash, which speeds up the transition to OD mode the next time the self-survey runs. You can manually restart the self-survey process with the gnss self-survey restart Cisco IOS command. After self-survey mode completes again, the results in the GNSS receiver flash are overwritten with the updated results.
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Over-determined (OD) clock mode: The device transitions to OD mode when self-survey mode is completed and the position information is stored in non-volatile memory on the device. In this mode, the GNSS receiver outputs timing information based on satellite positions obtained in self-survey mode.
The GNSS receiver remains in OD mode until there is a reason to leave it, such as:
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Detection of a position relocation of the antenna of more than 100m, which triggers an automatic restart of the self-survey.
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Manual restart of the self-survey using the gnss self-survey restart command.
After the GNSS receiver locks on to a satellite system, it sends a 10ms wide PPS pulse and the current time/date according to the satellite system to the Cisco IOS time service.
GNSS LED
The GNSS LED (labeled "GPS" on the cable side and power supply side LEDs) indicates the GNSS status. The following table shows LED colors and their meaning.
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Color |
Status |
|---|---|
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Blinking Green |
Attempting to acquire satellite fix. |
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Solid Green |
GNSS has valid signal/fix. |
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Blinking Amber |
Antenna fault. |
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Off |
GNSS not configured. |
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