GPS Synchronization
| Document revision: | 2.0 (Fri Mar 05 08:56:37 GMT 2004) |
| Applies to: | V2.8 |
General Information
Summary
Global Positioning System (GPS) receiver can be used by MikroTik RouterOS to get the precise location and time (which may be used as NTP time source)
Specifications
Packages required: gpsLicense required: Level1
Submenu level: /system gps
Standards and Technologies: GPS, NMEA 0183, Simple Text Output Protocol
Hardware usage: Not significant
Related Documents
Description
Global Positioning System (GPS) is used for determining precise location of a GPS receiver. There are two types of GPS service:
- Precise Positioning Service (PPS) that is used only by U. S. and Allied military, certain U. S. Government agencies, and selected civil users specifically approved by the U. S. Government. Its accuracy is 22m horizontally, 27.7m vertically and 200ns of time
- Standard Positioning Service (SPS) can be used by civil users worldwide without charge or restrictions except that SPS accuracy is intentionally degradated to 100m horizontally, 156m vertically and 340ns of time
GPS system is based on 24 satellites rotating on 6 different orbital planes with 12h orbital period. It makes that at least 5, but usually 6 or more satellites are visible at any time anywhere on the Earth. GPS receiver calculates more or less precise position (latitude, longitude and altitude) and time based on signals received from 4 satellites (three are used to determine position and fourth is used to correct time), which are broadcasting their current positions and UTC time.
MikroTik RouterOS can communicate with many GPS receivers which are able to send the positioning and time via asynchronous serial line using NMEA 0183, NMEA/RTCM or Simple Text Output Protocol. Note that you might need to configure the router's serial port in order to work with your device. For example, many GPS receivers work on 4800bit/s bitrate, to the same whould be set in the /port menu for the respective serial port.
Precise time is mainly intended to be used by built-in NTP server, which can use it as a time source without any additional configuration if GPS is configured to set system time.
Additional Resources
Synchronizing with a GPS Receiver
Submenu level: /system gpsProperty Description
enabled (yes | no) - whether the router will communicate with a GPS receiver or not port (name) - the port that will be used to communicate with a GPS receiver set-system-time (time) - whether to set the system time to the value received from a GPS receiver or notNotes
If you are synchronizing system time with a GPS device, you should correctly choose time zone if it is different from GMT as satellites are broadcasting GMT (a.k.a. UTC) time.
Example
To enable GPS communication through serial0 port:
[admin@MikroTik] system gps> print
enabled: no
port: (unknown)
set-system-time: yes
[admin@MikroTik] system gps> set enabled=yes port=serial0
[admin@MikroTik] system gps> print
enabled: yes
port: serial0
set-system-time: yes
[admin@MikroTik] system gps>
GPS Monitoring
Submenu level: /system gps monitorDescription
This command is used for monitoring the data received from a GPS receiver.
Property Description
date-and-time (read-only: text) - date and time received from GPS server longitude (read-only: text) - longitude of the current location latitude (read-only: text) - latitude of the current location altitude (read-only: text) - altitude of the current location speed (read-only: text) - mean velocity valid (read-only: yes | no) - whether the received information is valid or not (e.g. you can set a GPS receiver to the demo mode to test the connection, in which case you will receive information, but it will not be valid)Example
[admin@MikroTik] system gps> monitor
date-and-time: jul/23/2003 12:25:00
longitude: "E 24 8' 17''"
latitude: "N 56 59' 22''"
altitude: "-127.406400m"
speed: "0.001600 km/h"
valid: yes
[admin@MikroTik] system gps>