Configuring the Global Navigation Satellite System

Configuring the Global Navigation Satellite
System
Effective Cisco IOS-XE Release 3.17, the Cisco ASR 903 (with RSP3 module) and Cisco ASR 907 router
uses a satellite receiver, also called the global navigation satellite system (GNSS), as a new timing interface.
In typical telecom networks, synchronization works in a hierarchal manner where the core network is
connected to a stratum-1 clock and this clock is then distributed along the network in a tree-like structure.
However, with a GNSS receiver, clocking is changed to a flat architecture where access networks can directly
take clock from satellites in sky using an on-board GPS chips.
This capability simplifies network synchronization planning, provides flexibility and resilience in resolving
network synchronization issues in the hierarchical network.
• Information About the GNSS, page 1
• How to Configure the GNSS, page 3
• Configuration Example For Configuring GNSS, page 6
• Additional References, page 6
Information About the GNSS
Overview of the GNSS Module
The GNSS module is present on the front panel of the RSP3 module and can be ordered separately with PID=.
However, there is no license required to enable the GNSS module.
The GNSS LED on the RSP3 front panel indicates the status of the module. The following table explains the
different LED status.
LED Status
Description
Green
GNSS Normal State. Self survey is complete.
Amber
All other states
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Configuring the Global Navigation Satellite System
Operation of 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
The RSP3 module can also receive 1PPS, 10 MHz, and ToD signals from an external clocking and timing
source. However, the timing signals from the GNSS module (when enabled) take precedence over those
of the external source.
GNSS accuracy can be improved by using the high-accuracy operating mode. However, ensure the following:
• This mode significantly reduces the bandwidth of the Digital Phase Locked Loop (DPLL) clock. Therefore,
a sufficient stabilization period (less than 5 minutes) is required.
• During the stabilization period, the downstream PTP is stopped to avoid providing the degraded clock
to the slaves. Also, 1PPS from GNSS remains disabled.
Note
The high-accuracy mode requires 1PPS, ToD, and 10M as clock source to be configured along with GNSS.
By default, anti-jamming is enabled on the GNSS module.
Operation of the GNSS Module
The GNSS module has the following stages of acquiring and providing timing signals to the Cisco router:
• Self-Survey Mode—When the router is reset, the GNSS module comes up in self-survey mode. It tries
to lock on to minimum four different satellites and computes approximately 2000 different positions of
the satellites to obtain a 3-D location (Latitude, Longitude, and Height) of it 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.
When GNSS moves into Normal state, you can start using the 1PPS, 10 MHz, and ToD inputs from GNSS.
The quality of the signal in Self-Survey mode with Normal state is considered good enough to lock to GNSS.
• Over determined clock mode—The router switches to over determined (OD) mode when the self-survey
mode is complete and the position information is stored in 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, which is retained even when the router is reloaded. 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 unless one of the following conditions occur:
• A position relocation of the antenna of more than 100 meters is detected. This detection causes an
automatic restart of the self-survey mode.
• A manual restart of the self-survey mode or when the stored reference position is deleted.
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Configuring the Global Navigation Satellite System
High Availability for GNSS
• A worst-case recovery option after a jamming-detection condition that cannot be resolved with other
methods.
You can configure the GNSS module to automatically track any satellite or configure it to 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. GALILEO is not supported.
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 router’s physical location is changed to more than 100 m from it’s pre-reloaded condition.
High Availability for GNSS
The Cisco ASR 903 and Cisco ASR 907 routers have two GNSS modules, one each on the active and standby
RSP3 modules. Each GNSS module must have a separate connection to the antenna in case of an RSP3
switchover.
Prerequisites for GNSS
To use GNSS:
• 1PPS, 10 MHz, and ToD must be configured for netsync and PTP. For more information see the
Configuring Clocking and Timing chapter in the Cisco ASR 903 Router Chassis Software Configuration
Guide .
• The antenna should see as much as possible from the total sky. For proper timing, minimum of four
satellites should be locked. For information, see the Cisco ASR 903 Series Aggregation Services Router
Hardware Installation Guide .
Restrictions for GNSS
The GNSS module is not supported through SNMP; all configurations are performed through commands.
How to Configure the GNSS
Note
To know more about the commands referenced in this document, see the Cisco IOS Master Command
List .
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Configuring the Global Navigation Satellite System
Enabling the GNSS on the Cisco Router
Enabling the GNSS on the Cisco Router
enable
configure terminal
gnss slot r0
no shutdown
exit
Note
After the GNSS module is enabled, GNSS will be the source for 1PPS, ToD, and 10MHz clocking functions.
Configuring the Satellite Constellation for GNSS
enable
configure terminal
gnss slot r0
constellation [auto | gps | galelio | beidou | qzss
exit
Configuring Pulse Polarity
enable
configure terminal
gnss slot r0
1pps polarity negative
exit
Note
The no 1pps polarity negative command returns the GNSS to default mode (positive is the default value).
Configuring Cable Delay
enable
configure terminal
gnss slot r0
1pps offset 5
exit
Note
It is recommended to compensate 5 nanosecond per meter of the cable.
The no 1pps offset command sets cable delay offset to zero.
Configuring High-Accuracy Mode
enable
configure terminal
gnss slot r0
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Configuring the Global Navigation Satellite System
Disabling Anti-Jam Configuration
operating-mode high-accuracy
exit
Disabling Anti-Jam Configuration
enable
configure terminal
gnss slot
ro
anti-jam disable
exit
Verifying the Configuration of the GNSS
Use the show gnss status command to display status of GNSS.
Router# show gnss status
GNSS status:
GNSS device: detected
Lock status: Normal
Receiver Status: Auto
Clock Progress: Phase Locking
Survey progress: 100
Satellite count: 22
Holdover Duration: 0
PDOP: 1.04
TDOP: 1.00
HDOP: 0.73
VDOP: 0.74
Minor Alarm: NONE
Major Alarm: None
Use the show gnss satellite command to display the status of all satellite vehicles that are tracked by the
GNSS module.
Router# show gnss satellite all
All Satellites Info:
SV PRN No
Channel No
Acq Flg
Ephemeris Flg
SV Type
Sig Strength
---------------------------------------------------------------------------------14
0
1
1
0
47
21
2
1
1
0
47
22
3
1
1
0
46
18
4
1
1
0
47
27
6
1
1
0
44
31
8
1
1
0
49
24
10
1
1
0
42
79
12
0
1
1
18
78
13
1
1
1
26
Router# show gnss satellite 21
Selected Satellite Info:
SV PRN No: 21
Channel No: 2
Acquisition Flag: 1
Ephemeris Flag: 1
SV Type: 0
Signal Strength: 47
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Configuring the Global Navigation Satellite System
Configuration Example For Configuring GNSS
Use the show gnss time and show gnss location to display the time and location of the Cisco ASR 902 or
Cisco ASR907 router.
Router# show gnss time
Current GNSS Time:
Time: 2015/10/14
12:31:01 UTC Offset: 17
Router# show gnss location
Current GNSS Location:
LOC: 12:56.184000 N
77:41.768000 E 814.20 m
Configuration Example For Configuring GNSS
gnss slot R0
no shutdown
operating-mode high-accuracy
anti-jam disable
constellation glonass
1pps polarity negative
1pps offset 1000 negative
Additional References
Standards
Standard
Title
—
There are no associated standards for this feature,
MIBs
MIB
• There are no MIBs for this feature.
MIBs Link
To locate and download MIBs for selected platforms,
Cisco software releases, and feature sets, use Cisco
MIB Locator found at the following URL:
http://www.cisco.com/go/mibs
RFCs
RFC
Title
—
There are no associated RFCs for this feature.
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