Spectracom - Essential Ingenuity

Outputting position information

Question

How can current position information be provided by the time server?

Answer

One way that the time server can output position information (latitude, longitude and altitude) is via the associated SNMP “ssGpsRefTableEntry” OIDs.  This information is provided by an SMMP table reporting position information. These three individual OIDs are the only way to read position information via SNMP (there isn’t a single OID available that grabs latitude, longitude and altitude with a single poll, but SNMP can report the information via three individual OIDs). 
 
In addition to being able to use SNMP (or the front panel) to provide position information, there are a couple of other ways for SecureSync to output position. These include using the gpsloc CLI command via a telnet, SSH or RS-232 serial connection (as shown below).  After establishing the connection, enter this command and the time server will respond with the current position.
 
gpsloc CLI command
 
Lastly, another commonly used method to output position is via an ASCII output data stream, provided by an ASCII output Option Card (Spectracom Model 1204-02 for RS-232 output, or Model 1204-04 Option Card for RS-485 output) installed in the rear panel option "slots" (available on SecureSync and NetClock 9483 models). Both of these ASCII output Option Cards provide the ability to output several different selectable data streams, including NMEA formats GPGGA and GPRMC (which are the two data streams that can provide position information):

Below in bold are an example of both the GPGGA and GPRMC ASCII Data output formats, followed by a description of each of the fields in the data streams.  Note that the time server can be configured to output both of these mesaages back-to-back, as desired.

GPGGA

    $GPGGA,123519.00,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47
 
Where:
 

GGA = Global Positioning System Fix Data
123519.00 = Fix taken at 12:35:19 UTC
4807.038,N = Latitude 48 deg 07.038' N
01131.000,E = Longitude 11 deg 31.000' E
1 = Fix quality:
0 = Invalid
1 = GPS fix (SPS)
2 = DGPS fix
3 = PPS fix
4 = Real Time Kinematic
6 = estimated (dead reckoning) (2.3 feature)
7 = Manual input mode
8 = Simulation mode
08 = Number of satellites being tracked
0.9 = Horizontal dilution of position
545.4,M = Altitude, Meters, above mean sea level
46.9,M  = Height of geoid (mean sea level) above WGS84 ellipsoid
(empty field) = Time in seconds since last DGPS update
(empty field) = DGPS station ID number
*47    = the checksum data, always begins with *
 

 

GPRMC

     $GPRMC,123519.00,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A
 
Where:
 

RMC = Recommended Minimum sentence C
123519.00 = Fix taken at 12:35:19 UTC
A = Status A=active or V=Void.
4807.038,N = Latitude 48 deg 07.038' N
01131.000,E = Longitude 11 deg 31.000' E
022.4  = Speed over the ground in knots
084.4  = Track angle in degrees True
230394 = Date - 23rd of March 1994
003.1,W = Magnetic Variation
*6A = The checksum data, always begins with *
 
The Model 1204-02 and 1204-04 ASCII output Option Cards are available for retrofit into fielded units (given an empty option module "slot"). The SecureSync Option Cards/Modules Datasheet provide information on all Spectracom time server options.


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