The GNSS module is present on the front panel of the Route Processor (RP) module and can be ordered separately with PID=. However, there is no license required to enable the GNSS module.

When connected to an external antenna, the module can acquire satellite signals and track up to 32 GNSS satellites, and compute location, speed, heading, and time. GNSS provides an accurate one pulse-per-second (PPS), a stable 10 MHz frequency output to synchronize broadband wireless, aggregation and pre-aggregation routers, and an accurate time-of-day (ToD).

Note	We do not recommend that you configure both the front panel (10M, 1PPS and ToD) input configuration and the GNSS input configuration.

By default, anti-jamming is enabled on the GNSS module.

A GNSS module operates in one of these modes. Both modes acquire and provide timing signals to Cisco 8000 routers:

• Self-survey mode - When the router is reset, the GNSS module comes up in self-survey mode. It tries to lock on to a minimum of four different satellites and computes approximately 2000 different positions of the satellites to obtain a 3-D location (Latitude, Longitude, and Height) of its current position. This operation takes about 35 to 40 minutes. During this stage also, the module is able to generate accurate timing signals and achieve a Normal or Phase-locked state.

• Over-determined clock mode - The router switches to an over-determined (OD) mode when the self-survey mode is complete and the position information is stored in the non-volatile memory on the router. In this mode, the module only processes the timing information based on satellite positions captured in self-survey mode.

The router saves the tracking data. This tracking data is retained even after the router reload. If you want to change the tracking data, use the no shutdown command to set the GNSS interface to its default value.

The GNSS module stays in the OD mode until one of the following conditions occur:

• When the position relocation of the antenna of more than 100 meters is detected. This detection causes an automatic restart of the self-survey mode.

• When the self-survey mode is restarted manually.

• When the stored reference position is deleted.

• When a worst-case recovery scenario is considered after a jamming-detection condition that cannot be resolved with other methods.

You can configure the GNSS module to automatically track any satellite or explicitly use a specific constellation. However, the module uses configured satellites only in the OD mode.

Note	GLONASS and BeiDou satellites cannot be enabled simultaneously.

When the router is reloaded, it always comes up in the OD mode unless:

• The router is reloaded when the self-survey mode is in progress.

• The physical location of the router is changed to more than 100 m from its pre-reloaded condition.

When the system restarts GNSS self-survey by using the default gnss slot R0/R1 command in configuration mode, the 10MHz, 1PPS, and ToD signals are not changed and remain in the up state.

Note	The R1 slot is applicable only to specific modules that support dual RP.

• 1PPS, 10 MHz, and ToD must be configured for netsync and PTP.

• The antenna must have a clear view of the sky. For accurate timing, a minimum of four satellites should be locked.

• The GNSS module is not supported through SNMP; all configurations are performed through commands.

• The GNSS holdover performance is one microsecond in two hours of holdover after twelve hours of GNSS lock time.

A Cisco 8000 router can act in Primary Reference Time Clock (PRTC) mode, when GNSS is locked and no telecom profiles are configured. In PRTC mode, the router provides ToD + 1PPS output with ToD in UBX format.

Once the router is in PRTC mode, ordinary clock and transparent clocks are not supported under LAN profiles. All boundary clocks under LAN profiles will be in GMC-BC mode, which fetches timestamps and grandmaster clock details as per the GNSS input.

The GMS-BC master clock provides these clock quality values.

Clock Quality:
    Class: 6                        //----GNSS CLASS
    Accuracy: Within 250ns          //----GNSS Accuracy
    Offset (log variance): 20061    //----GNSS Variance

PRTC mode is supported on PTP Default and Power profile. The conversion takes place automatically when GNSS moves to locked state.

Note	GNSS cannot be configured when the one of the following is configured: 802.1AS PTP TC mode GMC-BC options

This table provides information about the GNSS class supported on the Cisco 8000 series routers and line cards.