Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 
ON THIS PAGE
 

GNSS Configuration for Routers

This topic describes how to configure a GNSS receiver on routers.

Some Juniper routers support the G.8275.1 profile—Telecom Grandmaster (T-GM) functionality using an external TB-1 GNSS receiver. There are several benefits of the TB-1 receiver with the T-GM functionality which include:

  • Compliance to ITU-T G.8272 (Unified functional architecture for transport networks) PRTC Class A.

  • Support for multiple constellations such as GPS, GLONAS, QZSS and Galileo.

  • Support for multipath spoofing, jamming, interference detection and isolation mechanisms.

  • Supported on 10G and 25G ports for all devices in the network.

Commands to Configure the T-GM Functionality

Use the following commands to configure the T-GM functionality:

  • set chassis synchronization gnss-receiver <(0|1)> receiver-type <name>

  • set chassis synchronization gnss-receiver <(0|1)> interface

Commands to Enable GM Functionality

Use the following commands to enable GM functionality:

  • set protocols ptp clock-mode ordinary

  • set protocols ptp profile-type g.8275.1

  • set protocols ptp master interface <interface-name> multicast-mode transport ieee-802.3

  • ptp-mode

  • gnss-receiver

  • show chassis synchronization gnss-receiver extensive

  • show chassis synchronization extensive

  • show ptp lock-status detail

In T-GM mode the router functions as an ordinary clock and all the PTP configured ports are in "TimeTransmitter only" state. Up to 512 timeTransmitter ports are supported on the routers.

Note:

  • ACX7024 and ACX7024X routers support this functionality.

  • A synchronous Ethernet (SyncE) input is not allowed when system is functioning as a T-GM. Use the following command to configure a wait-to-restore check for SyncE input:

    set chassis synchronization source interfaces et-0/0/4 quality-level prc wait-to-restore 0

  • Ensure that at least one of configured timeTransmitter port link is up, else the show ptp lock-status command will keep displaying the status as Initializing and show chassis synchronization extensive command will keep displaying the current clock status as Freerun.

Configure GNSS Receiver for Telecom Grandmaster (T-GM)

The TB-1 GNSS receiver is designed to operate with multiple constellations. When connected to an external GNSS antenna, the receiver contains all the circuitry necessary to automatically acquire GNSS satellite signals, track GNSS satellites, and acquire precise position and timing solutions. It provides 1 pulse-per-second (PPS) precision timing and stable 10-MHz frequency output.

To optimize the GNSS capability, establish a common time scale and coordinated system between all the systems. This coordinated system simplifies network synchronization, and provides flexibility and resiliency.

Table 1 describes the steps to configure GNSS receiver on the supported routers.

Table 1: GNSS Receiver Configuration

Configuration Step

Command

Step 1: (Mandatory) Enable GNSS receiver and grandmaster clock functionality.

Enable the GNSS receiver by using the gnss-receiver 0 interface statement at the edit chassis synchronization hierarchy level. By enabling the GNSS receiver, you establish communication between the router with the GNSS receiver.

Configure the satellite constellation by using the gnss-receiver 0 constellation statement at the edit chassis synchronization hierarchy level. Various constellations are available. Through this configuration, you can configure the GNSS receiver to explicitly use a specific constellation or combination of constellations.

For more information, see clock-mode, profile-type, transport-ieee-802.3, gnss-receiver, and ptp-mode.

Note:

When ptp-mode is enabled, port 27 is no longer available for use.

  1. Set clock mode.

    [edit protocols ptp]
user@host# set clock-mode ordinary

  2. Set G.8275.1 profile type.

    [edit protocols ptp]
user@host# set profile-type g.8275.1

  3. Set transport protocol as IEEE 802.3. 

    [edit protocols ptp master interface interface name multicast-mode]
user@host# set transport ieee-802.3

  4. Set the GNSS receiver interface. 

    [edit chassis synchronization gnss-receiver number]
user@host# set interface

  5. (Optional) Set the holdover-in-spec-duration configuration.

    [edit protocols ptp]
user@host# set protocols ptp holdover-in-spec-duration time duration

  6. Configure the GNSS receiver type as TB-1. 

    [edit chassis synchronization gnss-receiver number]
user@host# set receiver-type tb-1

  7. Set the GNSS receiver constellation. 

    [edit chassis synchronization gnss-receiver number]
user@host# set constellation

  8. Set PTP mode for FPC and PIC.

    [edit chassis fpc 0 pic 0]
user@host# set ptp-mode

Step 2: (Optional) Specify the position mode. TB-1 as timing receiver has two different position modes— position-fix-mode and survey-mode. The default position mode is survey-mode if no specific mode is configured.

  • position-fix-mode: Use this mode when you know the accurate antenna location.

  • survey-mode: Use this mode when you do not know the fixed location of the antenna.

For more information about position mode, see gnss-receiver.

 
[edit chassis synchronization gnss-receiver number]
user@host# set position-mode

Step 3: (Optional) Specify the antenna cable delay compensation value. This configuration is used to compensate the delay introduced due to RF cable which is routed from antenna to TB-1 RF input.

You can also use this command to compensate the PPS cable delay by adding both RF cable and PPS cable delays.

For long cable runs, this delay can be significant. The range is from -1000000 to 1000000 nanoseconds.

For more information about cable delay compensation, see gnss-receiver.

 
[edit chassis synchronization gnss-receiver number]
user@host# set cable-delay-compensation value
Note:

Refer https://timesmicrowave.com/calculator/ to calculate the antenna cable delay compensation value and mention it in the command.

For example, if the antenna cable delay compensation is 1000 nanoseconds, then the command should be set cable-delay-compensation -1000. Note the negative value for the delay.

Step 4: (Optional) Specify the Signal-to-Noise Ratio (SNR) threshold value.

The SNR is the ratio of the signal power to the noise power. GNSS receiver measures SNR value to indicate the signal strength of the received satellite signal and the noise density. You can configure the SNR threshold value. Satellites with the signal level equal to or above the threshold value can only be used for positioning.

  • range: 0 - 99 dBHz

For more information about SNR threshold, see gnss-receiver.

 
[edit chassis synchronization gnss-receiver number]
user@host# set snr-threshold value

Step 5: Commit the configuration.

 
[edit]
user@host# commit

Step 6: Verify the configuration.

For more information about the operational commands, see show chassis synchronization gnss-receiver extensive, show chassis synchronization extensive, and show ptp lock-status detail.

Note:

Ensure that at least one of configured timeTransmitter port link is up, else the show ptp lock-status command will keep displaying the status as Initializing and show chassis synchronization extensive command will keep displaying the current clock status as Freerun.

 
[edit]
user@host# run show chassis synchronization gnss-receiver extensive
[edit]
user@host# run show chassis synchronization extensive
[edit]
user@host# run show ptp lock-status detail
[edit]
user@host# run show ptp clock detail

Troubleshoot GNSS Receiver

Alarms

In case of any issues, run the show chassis alarms command to verify the following:

  • TB-1 is not detected or not connected in the USB port.

  • 1PPS is not detected or connected.

  • 10 MHz is not detected or connected.

Sample Output