The purpose of BNC is to

• retrieve real-time GNSS data streams available through NTRIP transport protocol,
• retrieve real-time GNSS data streams via TCP directly from an IP address without using the NTRIP transport protocol, and/or
• retrieve real-time GNSS data streams from a serial port without using the NTRIP transport protocol, and/or
• generate high-rate RINEX Observation and Navigation files to support near real-time GNSS post-processing applications, and/or
• generate ephemeris and synchronized or unsynchronized observations epoch by epoch through an IP port to support real-time GNSS network engines, and/or
• generate clock and orbit corrections to broadcast ephemeris through an IP port to support real-time Precise Point Positioning on GNSS rovers, and/or
• generate synchronized clock and orbit corrections to broadcast ephemeris epoch by epoch through an IP port to support the combination of such streams as coming simultaneously from various correction providers, and/or
• monitor the performance of a network of real-time GNSS data streams to generate advisory notes, and/or
• scan RTCM streams for incoming antenna information as well as message types and their repetition rates, and/or
• feed a stream into a GNSS receiver via serial communication link.

BNC supports the following GNSS data formats:

• RTCM Version 2.x containing message types 18 and 19 or 20 and 21 together with 3 and 22 (GPS and GLONASS),
• RTCM Version 3.x containing message types 1002 (GPS, SBAS) or 1004 (GPS), 1010 or 1012 (GLONASS), 1019 or 1020 (broadcast ephemeris), 3001-3012 (premature messages for combined orbit and clock corrections to GPS and GLONASS broadcast ephemeris)
• RTIGS containing GPS record types 200 (observations) and 300 (ephemeris).

Although BNC is a real-time tool to be operated in online mode, it can be run offline for post processing of data made availabe from a file. Furthermore, apart from its regular window mode, BNC can be run as a batch/background job in a 'no window' mode using processing options from previously saved configuration.

Unless in offline mode, BNC

• requires access to the Internet with a minimum of about 2 to 6 kbits/sec per stream depending on the stream format and the number of visible satellites. You need to make sure that the connection can sustain the required bandwidth.
• requires the clock of the host computer to be properly synchronized.
• has the capacity to retrieve hundreds of GNSS data streams simultaneously. Please be aware that such usage may incur a heavy load on the NTRIP broadcaster side depending on the number of streams requested. We recommend limiting the number of streams where possible to avoid unnecessary workload.

This section describes BNC's top menu bar, its processing options and bottom menu bar.

The usual handling of BNC is that you first select a number of streams ('Add Streams'). Any stream configured to BNC shows up on the 'Streams' canvas in the middle of BNC's main window. You then go through BNC's various tabs to select a combination of processing options before you start the program ('Start'). Records of BNC's activities are shown in the 'Logs' canvas on the bottom of the main window.

As a default, configuration files for running BNC on Unix/Linux/Mac systems are saved in directory '${HOME}/.config/BKG'. On Windows systems, they are typically saved in directory 'C:/Documents and Settings/Username/.config/BKG'. The default configuration file name is 'BNC.ini'.

The default file name 'BNC.ini' can be changed and the file contents can easily be edited. On graphical user interfaces it is possible to Drag & Drop a configuration file icon to start BNC. Some configuration options can be changed on-the-fly. See annexed 'Configuration Example' for a complete set of configuration options.

The top menu bar allows to select a font for the BNC windows, save configured options or quit the program execution. It also provides access to a program documentation.

The 'File' button lets you

• select an appropriate font.
  Use smaller font size if the BNC main window exceeds the size of your screen.
• save selected options in configuration file.
  When using 'Save & Activate Options' while BNC is already processing data, some configuration options become immediately effective on-the-fly without interrupting uninvolved threads. See annexed section 'Configuration Example' for a list of on-the-fly changeable configuration options.
• quit the BNC program.

The 'Help' button provides access to

• help contents.
  You may keep the 'Help Contents' window open while configuring BNC.
• a 'Flow Chart' showing BNC linked to a real-time GNSS network engine such as RTNet.
• general information about BNC.
  Close the 'About BNC' window to continue working with BNC.

BNC comes with a help system providing online information about its functionality and usage. Short descriptions are available for any widget. Focus to the relevant widget and press Shift+F1 to request help information. A help text appears immediately; it disappears as soon as the user does something else. The dialogs on some operating systems may provide a "?" button that users can click; they then click the relevant widget to pop up the help text.

If you are running BNC within a protected Local Area Network (LAN), you might need to use a proxy server to access the Internet. Enter your proxy server IP and port number in case one is operated in front of BNC. If you don't know the IP and port of your proxy server, check the proxy server settings in your Internet browser or ask your network administrator.

Note that IP streaming is often not allowed in a LAN. In this case you need to ask your network administrator for an appropriate modification of the local security policy or for the installation of a TCP relay to the NTRIP broadcasters. If these are not possible, you might need to run BNC outside your LAN on a host that has unobstructed connection to the Internet.

The following defines general settings for BNC's logfile, file handling, reconfiguration on-the-fly, and auto-start.

Records of BNC's activities are shown in the 'Logs' canvas on the bottom of the main window. These logs can be saved into a file when a valid path is specified in the 'Logfile (full path)' field. The logfile name will automatically be extended by a string '_YYMMDD' carrying the current date. This leads to series of daily logfiles when running BNC continuously for extended. Message logs cover the communication status between BNC and the NTRIP broadcaster as well as problems that may occur in the communication link, stream availability, stream delay, stream conversion etc. All times are given in UTC. The default value for 'Logfile (full path)' is an empty option field, meaning that BNC logs will not saved into a file.

When BNC is started, new files are created by default and any existing files with the same name will be overwritten. However, users might want to append existing files following a restart of BNC, a system crash or when BNC crashed. Tick 'Append files' to continue with existing files and keep what has been recorded so far. Note that option 'Append files' affects all types of files created by BNC.

When operating BNC online in 'no window' mode (command line option -nw), some configuration options can nevertheless be changed on-the-fly without interrupting the running process. For that you force the program to reread parts of its configuration in pre-defined intervals from the disk. Select '1 min', '1 hour', or '1 day' to let BNC reread on-the-fly changeable configuration options every full minute, hour, or day. This lets in between edited options become effective without interrupting uninvolved threads. See annexed section 'Configuration Example' for a configuration file example and a list of on-the-fly changeable options.

You may like to auto-start BNC at startup time in window mode with preassigned configuration options. This may be required i.e. immediately after booting your system. Tick 'Auto start' to supersede the usage of the 'Start' button. Make sure that you maintain a link to BNC for that in your Autostart directory (Windows systems) or call BNC in a script below directory /etc/init.d (Unix/Linux/Mac systems).

See BNC's command line option -nw for an auto-start of BNC in 'no window' mode.

Observations will be converted to RINEX if they come in either RTCM Version 2.x, RTCM Version 3.x, or RTIGS format. BNC's RINEX Observation files generally contain C1, C2, P1, P2, L1, L2, S1, and S2 observations. In case an observation is unavailable, its value is set to zero '0.000'. Note that the 'RINEX TYPE' field in the RINEX Observation file header is always set to 'M(MIXED)' even if the file does not contain any GLONASS or SABAS data.

RINEX file names are derived by BNC from the first 4 characters of the corresponding stream's mountpoint (4Char Station ID). For example, data from mountpoints FRANKFURT and WETTZELL will have hourly RINEX Observation files named

FRAN{ddd}{h}.{yy}O
WETT{ddd}{h}.{yy}O

where 'ddd' is the day of year, 'h' is a letter which corresponds to an hour long UTC time block and 'yy' is the year.

If there are more than one stream with identical 4Char Station ID (same first 4 characters for their mountpoints), the mountpoint strings are split into two sub-strings and both become part of the RINEX file name. For example, when simultaneously retrieving data from mountpoints FRANKFURT and FRANCE, their hourly RINEX Observation files are named as

FRAN{ddd}{h}_KFURT.{yy}O
FRAN{ddd}{h}_CE.{yy}O.

If several streams show exactly the same mountpoint name (example: BRUS0 from www.euref-ip.net and BRUS0 from www.igs-ip.net), BNC adds an integer number to the file name leading i.e. to hourly RINEX Observation files like

BRUS{ddd}{h}_0.{yy}O
BRUS{ddd}{h}_1.{yy}O.

Note that RINEX file names for all intervals less than 1 hour follow the file name convention for 15 minutes RINEX Observation files i.e.

FRAN{ddd}{h}{mm}.{yy}O

where 'mm' is the starting minute within the hour.

Here you can specify the path to where the RINEX Observation files will be stored. If the specified directory does not exist, BNC will not create RINEX Observation files. Default value for 'Directory' is an empty option field, meaning that no RINEX Observation files will be written.

Select the length of the RINEX Observation file generated. The default value is 15 minutes.

Select the RINEX Observation sampling interval in seconds. A value of zero '0' tells BNC to store all received epochs into RINEX. This is the default value.

Whenever BNC starts generating RINEX Observation files (and then once every day at midnight), it first tries to retrieve information needed for RINEX headers from so-called public RINEX header skeleton files which are derived from sitelogs. A HTTP link to a directory containing these skeleton files may be available through data field number 7 of the affected NET record in the source-table. See http://www.epncb.oma.be:80/stations/log/skl/brus.skl for an example of a public RINEX header skeleton file for the Brussels EPN station.

However, sometimes public RINEX header skeleton files are not available, its contents is not up to date, or you need to put additional/optional records in the RINEX header. For that BNC allows using personal skeleton files that contain the header records you would like to include. You can derive a personal RINEX header skeleton file from the information given in an up to date sitelog. A file in the RINEX Observations 'Directory' with a 'Skeleton extension' suffix is interpreted by BNC as a personal RINEX header skeleton file for the corresponding stream.

Examples for personal skeleton file name convention: RINEX Observation files for mountpoints WETTZELL, FRANKFURT and FRANCE (same 4Char Station ID), BRUS0 from www.euref-ip.net and BRUS0 from www.igs-ip.net (same 4Char Station ID, identical mountpoint stings) would accept personal skeleton files named

WETT.skl
FRAN_KFURT.skl
FRAN_CE.skl
BRUS_0.skl
BRUS_1.skl

if 'Skeleton extension' is set to 'skl'.

Note the following regulations regarding personal RINEX header skeleton files:

• If such a file exists in the 'RINEX directory', the corresponding public RINEX header skeleton file is ignored. The RINEX header is generated solely from the contents of the personal skeleton.
• Personal skeletons should contain a complete first header record of type

-   RINEX VERSION / TYPE
• They should then contain an empty header record of type

-   PGM / RUN BY / DATE
BNC will complete this line and include it in the actual RINEX file header.
• They should further contain complete header records of type

-   MARKER NAME
-   OBSERVER / AGENCY
-   REC # / TYPE / VERS
-   ANT # / TYPE
-   APPROX POSITION XYZ
-   ANTENNA: DELTA H/E/N
-   WAVELENGTH FACT L1/2
• They may contain any other optional complete header record as defined in the RINEX documentation.
• They should then contain empty header records of type

-   # / TYPES OF OBSERV
-   TIME OF FIRST OBS
BNC will include these lines in the final RINEX file header together with an additional
-   COMMENT
line describing the source of the stream.
• They should finally contain an empty header record of type

-   END OF HEADER (last record)

If neither a public nor a personal RINEX header skeleton file is available for BNC, a default header will be used.

Whenever a RINEX Observation file is saved, you might want to compress, copy or upload it immediately via FTP. BNC allows you to execute a script/batch file to carry out these operations. To do that specify the full path of the script/batch file here. BNC will pass the RINEX Observation file path to the script as a command line parameter (%1 on Windows systems, $1 on Unix/Linux/Mac systems).

The triggering event for calling the script or batch file is the end of a RINEX Observation file 'Interval'. If that is overridden by a stream outage, the triggering event is the stream reconnection.

As an alternative to initiating file uploads through BNC, you may like to call an upload script or batch file through your crontable or Task Scheduler (independent from BNC) once every 2 or 3 minutes after the end of each RINEX file 'Interval'.

The default format for RINEX Observation files is RINEX Version 2.11. Select 'Version 3' if you would like to save observations in RINEX Version 3 format.

Broadcast ephemeris can be saved as RINEX Navigation files when received via RTCM Version 3.x as message types 1019 (GPS) and 1020 (GLONASS) or via RTIGS records type 300. The file name convention follows the details given in section 'RINEX File Names' except that the first four characters are 'BRDC' and the last character is

• 'N' or 'G' for GPS or GLONASS ephemeris in two separate RINEX Version 2.11 Navigation files, or
• 'P' for GPS plus GLONASS ephemeris saved together in one RINEX Version 3 Navigation file.

Specify the path for saving broadcast ephemeris data as RINEX Navigation files. If the specified directory does not exist, BNC will not create RINEX Navigation files. Default value for Ephemeris 'Directory' is an empty option field, meaning that no RINEX Navigation files will be created.

Select the length of the RINEX Navigation file generated. The default value is 1 day.

BNC can output broadcast ephemeris in RINEX Version 3 ASCII format on your local host (IP 127.0.0.1) through an IP 'Port'. This function is introduced in order to support i.e. the 'BKG Ntrip Sate Space Server' (BNS) which transforms IGS clocks and orbits into corrections to broadcast ephemeris. Specify an IP port number to activate this function. The default is an empty option field, meaning that no ASCII ephemeris output via IP port is generated.

The source code for BNC comes with an example perl script 'test_bnc_eph.pl' that allows you to read BNC's ASCII ephemeris output from the IP port.

Default format for RINEX Navigation files containing broadcast ephemeris is RINEX Version 2.11. Select 'Version 3' if you want to save the ephemeris in RINEX Version 3 format.

Note that this does not concern the broadcast ephemeris output throug IP port which is always in RINEX Version 3 format.

• Message type 3001: GPS orbit corrections to Broadcast Ephemeris
• Message type 3002: GPS clock corrections to Broadcast Ephemeris
• Message type 3003: GPS code biases
• Message type 3004: Combined orbit and clock corrections to GPS Broadcast Ephemeris
• Message type 3005: GPS User Range Accuracy (URA)
• Message type 3006: High-rate GPS clock corrections to Broadcast Ephemeris
• Message type 3007: GLONASS orbit corrections to Broadcast Ephemeris
• Message type 3008: GLONASS clock corrections to Broadcast Ephemeris
• Message type 3009: GLONASS code biases
• Message type 3010: Combined orbit and clock corrections to GLONASS Broadcast Ephemeris
• Message type 3011: GLONASS User Range Accuracy (URA)
• Message type 3012: High-rate GLONASS clock corrections to Broadcast Ephemeris

RTCM Version 3 streams carrying these messages may be used i.e. to support real-time Precise Point Positioning (PPP) applications.

When using clocks from Broadcast Ephemeris (with or without corrections) and clocks from SP3 files in the same application, it is important to understand that Broadcast Ephemeris clocks - according to the Interface Control Documents (ICD) - are corrected for the 2nd-order relativistic effect whereas clocks from SP3 files are not. The 2nd-order relativistic effect is a priodic time correction defined as -2 (R * V) / c^2 and includes the scalar product of satallite position and velocity divided by the speed of light raised to the second power.

Specify a directory for saving Broadcast Corrections in files. If the specified directory does not exist, BNC will not create Broadcast Correction files. Default value for Broadcast Corrections 'Directory' is an empty option field, meaning that no Broadcast Correction files will be created.

The file name convention for Broadcast Correction files follows the convention for RINEX files except for the last character of the file name suffix which is set to "C".

The saved file contains the following information in plain ASCII format:

• GPS Week
• Second in GPS Week
• GNSS Indicator and Satellite Vehicle Pseudo Random Number
• IOD refering to Broadcast Ephemeris set
• Clock Correction to Broadcast Ephemeris [m]
• Radial Component of Orbit Correction to Broadcast Ephemeris [m]
• Along-track Component of Orbit Correction to Broadcast Ephemeris [m]
• Cross-track Component of Orbit Correction to Broadcast Ephemeris [m]

Example file contents:

...
1490 115710.0 G27    97      5.291      1.201   -1.964    0.821
1490 115710.0 G26    14    -11.247      1.003   -1.168    0.074
...

Select the length of the Broadcast Correction files. The default value is 1 day.

BNC can output epoch by epoch synchronized Broadcast Corrections in ASCII format on your local host (IP 127.0.0.1) through an IP 'Port'. Specify an IP port number to activate this function. The default is an empty option field, meaning that no Broadcast Correction output via IP port is generated.

The output format equals the format used for saving Broadcast Corrections in a file with the exception that the Mountpoint is added at each line's end.

The following is an example output from two RTCM Version 3 streams (CLCK1 and CLCK4) containing message types 3004 and 3010:

...
1490 115710.0 R17    18     -1.903      2.348   -1.343   -1.403 CLCK1
1490 115710.0 R10    18     -4.131      2.416   -0.646   -1.054 CLCK1
1490 115710.0 G27    97      5.291      1.201   -1.964    0.821 CLCK4
1490 115710.0 G26    14    -11.247      1.003   -1.168    0.074 CLCK4
...
1490 115711.0 R17    18     -1.902      2.349   -1.342   -1.403 CLCK1
1490 115711.0 R10    18     -4.131      2.415   -0.647   -1.052 CLCK1
1490 115711.0 G27    97      5.288      1.200   -1.964    0.820 CLCK4
1490 115711.0 G26    14    -11.246      1.004   -1.168    0.074 CLCK4
...

The source code for BNC comes with an example perl script 'test_bnc_eph.pl' that allows you to read BNC's Broadcast Corrections from the IP port.

When feeding a real-time GNSS network engine waiting epoch by epoch for synchronized Broadcast Corrections, BNC drops (only concering IP port output) whatever is received later than 'Wait for full epoch' seconds. A value of 2 to 5 seconds could be an appropriate choice for that, depending on the latency of the incoming Broadcast Corrections stream and the delay acceptable by your application. A message such as "COCK1: Correction overaged by 5 sec" shows up in BNC's logfile if 'Wait for full epoch' is exceeded.

BNC can generate synchronized or unsynchronized observations epoch by epoch from all stations and satellites to feed a real-time GNSS network engine. The output can be produced in a binary format through an IP port and/or a plain ASCII format to save the observations in a local file. It comprises the following observations where available:

StatID, SVPRN, GPSWeek, GPSWeeks, C1, C2, P1, P2, L1, L2, slip_cnt_L1, slip_cnt_L2, lock_timei_L1, lock_timei_L2, S1, S2, SNR1, SNR2

Note that slip_cnt stands for the cumulative loss of continuity indicator, lock_timei for the lock time indicator, and SNR for the signal-to-noise ratio 'S' mapped to integer numbers 1 to 9. In case an observation is not available, its value is set to zero '0.000'. Loss of continuity indicator and lock time indicator are set to nedative values if undefined.

The binary output is a continuous stream in the following order:

begEpoch
t_obsInternal
t_obsInternal
...
t_obsInternal
endEpoch
begEpoch
t_obsInternal
...

The corresponding structures are defined as follow:

  const char begEpoch[] = "BEGEPOCH";
  const char endEpoch[] = "ENDEPOCH";
...
...
class t_obsInternal {
 public:
  int    flags;
  char   StatID[20+1];  // Station ID
  char   satSys;        // Satellite System ('G' or 'R')
  int    satNum;        // Satellite Number (PRN for GPS NAVSTAR)
  int    slot;          // Slot Number (for Glonass)
  int    GPSWeek;       // Week of GPS-Time
  double GPSWeeks;      // Second of Week (GPS-Time)
  double C1;            // CA-code pseudorange (meters)
  double C2;            // CA-code pseudorange (meters)
  double P1;            // P1-code pseudorange (meters)
  double P2;            // P2-code pseudorange (meters)
  double L1;            // L1 carrier phase (cycles)
  double L2;            // L2 carrier phase (cycles)
  int    slip_cnt_L1;   // L1 cumulative loss of continuity indicator (negative value = undefined)
  int    slip_cnt_L2;   // L2 cumulative loss of continuity indicator (negative value = undefined)
  int    lock_timei_L1; // L1 last lock time indicator                (negative value = undefined)
  int    lock_timei_L2; // L2 last lock time indicator                (negative value = undefined)
  double S1;            // L1 signal-to noise ratio
  double S2;            // L2 signal-to noise ratio
  int    SNR1;          // L1 signal-to noise ratio (mapped to integer)
  int    SNR2;          // L2 signal-to noise ratio (mapped to integer)
};

The source code for BNC comes with an example program called 'test_bnc_qt.cpp' that allows you to read BNC's (synchronized or unsynchronized) binary observation output from the IP port and print the observations in a plain ASCII format on standard output.

Note that any socket connection of an application to BNC's synchronized or unsynchronized observations ports is recorded in the 'Logs' canvas on the bottom of the main window together with a connection counter, resulting in log records like 'New client connection on sync/usync port: # 1'.

BNC can produce synchronized observations in binary format on your local host (IP 127.0.0.1) through an IP 'Port'. Scynchronized means that BNC collects all data for any specific epoch which become available within a certain number of latency seconds (see 'Wait for Full Epoch' option). It then - epoch by epoch - outputs whatever has been received. Specify an IP port number here to activate this function. The default is an empty option field, meaning that no binary synchronized output is generated.

When feeding a real-time GNSS network engine waiting for synchronized input epoch by epoch, BNC drops whatever is received later than 'Wait for full epoch' seconds. A value of 3 to 5 seconds could be an appropriate choice for that, depending on the latency of the incoming streams and the delay acceptable for your real-time GNSS product. Default value for 'Wait for full epoch' is 5 seconds.

Note that 'Wait for full epoch' does not effect the RINEX Observation file content. Observations received later than 'Wait for full epoch' seconds will still be included in the RINEX Observation files.

Select the synchronized observation output sampling interval in seconds. A value of zero '0' tells BNC to send/store all received epochs. This is the default value.

Specifies the full path to a 'File' where synchronized observations are saved in plain ASCII format. The default value is an empty option field, meaning that no ASCII output file is created.

Beware that the size of this file can rapidly increase depending on the number of incoming streams. This option is primarily meant for testing and evaluation.

BNC can produce unsynchronized observations from all configured streams in binary format on your local host (IP 127.0.0.1) through an IP 'Port'. Unscynchronized means that BNC immediately forwards any received observation to the port. Specify an IP port number here to activate this function. The default is an empty option field, meaning that no binary unsynchronized output is generated.

You may use BNC to feed a serial connected device like an GNSS receiver. For that one of the incoming streams can be forwarded to a serial port.

Enter a 'Mountpoint' to forward its corresponding stream to a serial connected GNSS receiver.

When selecting the serial communication options listed below, make sure that you pick those configured to the serial connected receiver.

Enter the serial 'Port name' selected on your host for communication with the serial connected receiver. Valid port names are

Windows:       COM1, COM2
Linux:         /dev/ttyS0, /dev/ttyS1
FreeBSD:       /dev/ttyd0, /dev/ttyd1
Digital Unix:  /dev/tty01, /dev/tty02
HP-UX:         /dev/tty1p0, /dev/tty2p0
SGI/IRIX:      /dev/ttyf1, /dev/ttyf2
SunOS/Solaris: /dev/ttya, /dev/ttyb

Note that you must plug a serial cable in the port defined here before you start BNC.

Select a 'Baud rate' for the serial output link. Note that using a high baud rate is recommended.

Select a 'Flow control' for the serial output link. Note that your selection must equal the flow control configured to the serial connected device. Select 'OFF' if you don't know better.

Select the 'Parity' for the serial output link. Note that parity is often set to 'NONE'.

Select the number of 'Data bits' for the serial output link. Note that often '8' data bits are used.

Select the number of 'Stop bits' for the serial output link. Note that often '1' stop bit is used.

Select 'Auto' to automatically forward all NMEA-GGA messages coming from your serial connected GNSS receiver to the NTRIP broadcaster and/or save them in a file.

Forwarding valid NMEA-GGA messages to the NTRIP broadcaster is required for receiving 'Virtual Reference Station' (VRS) streams. Thus, in case your serial connected receiver is not capable to provide them, the alternative for VRS streams is a 'Manual' simulation of an initial NMEA-GGA message. Its contents is based on the approximate (editable) latitude/longitude from the broadcaster's source-table and an approximate VRS height to be specified.

In summary: select 'Manual' only when handling a VRS stream and your serial connected GNSS receiver doesn't generate NMEA-GGA messages. Select 'Auto' otherweise.

Specify the full path to a file where NMEA messages coming from your serial connected receiver are saved.

Specify an approximate 'Height' above mean sea level in meter for your VRS to simulate an inital NMEA-GGA message. Latitude and longitude for that (editable) are taken from the broadcaster's source-table.

This option concerns only 'Virtual Reference Stations' (VRS). Its setting is ignored in case of streams coming from physical reference stations.

At various times, the incoming stream might become unavailable or corrupted. In such cases, it is important that the BNC operator and/or the stream providers become aware of the situation so that necessary measures can be taken to restore the stream. Furthermore, continuous attempts to decode corrupted stream(s) can generate unnecessary workload for BNC. Outages and corruptions are handled by BNC as follows:

Stream outages: BNC considers a connection to be broken when there are no incoming data detected for more than 20 seconds. When this occurs, BNC will attempt to reconnect at a decreasing rate. It will first try to reconnect with 1 second delay, and again in 2 seconds if the previous attempt failed. If the attempt is still unsuccessful, it will try to reconnect within 4 seconds after the previous attempt and so on. The wait time doubles each time with a maximum wait time of 256 seconds.

Stream corruption: Not all bits chunk transfers to BNC's internal decoders return valid observations. Sometimes several chunks might be needed before the next observation can be properly decoded. BNC buffers all the outputs (both valid and invalid) from the decoder for a short time span (size derived from the expected 'Observation rate') and then determines whether a stream is valid or corrupted.

Outage and corruption events are reported in the 'Logs' canvas. They can also be passed on as parameters to a shell script or batch file to generate an advisory note to BNC operator or affected stream providers. This functionality lets users utilise BNC as a real-time performance monitor and alarm system for a network of GNSS reference stations.

BNC can collect all returns (success or failure) coming from a decoder within a certain short time span to then decide whether a stream has an outage or its content is corrupted. This procedure needs a rough a priory estimate of the expected observation rate of the incoming streams.

An empty option field (default) means that you don't want an explicit information from BNC about stream outages and incoming streams that can not be decoded.

Event 'Begin_Failure' will be reported if no data is received continuously for longer than the 'Failure threshold' time. Similarly, event 'Begin_Corrupted' will be reported when corrupted data is detected by the decoder continuously for longer than this 'Failure threshold' time. The default value is set to 15 minutes and is recommended so not to innundate user with too many event reports.

Note that specifying a value of zero '0' for the 'Failure threshold' will force BNC to report any stream failure immediately. Note also that for using this function you need to specify the 'Observation rate'.

Once a 'Begin_Failure' or 'Begin_Corrupted' event has been reported, BNC will check for when the stream again becomes available or uncorrupted. Event 'End_Failure' or 'End_Corrupted' will be reported as soon as valid observations are again detected continuously throughout the 'Recovery threshold' time span. The default value is set to 5 minutes and is recommended so not to innundate users with too many event reports.

Note that specifying a value of zero '0' for the 'Recovery threshold' will force BNC to report any stream recovery immediately. Note also that for using this function you need to specify the 'Observation rate'.

As mentioned previously, BNC can trigger a shell script or a batch file to be executed when one of the events described are reported. This script can be used to email an advisory note to network operator or stream providers. To enable this feature, specify the full path to the script or batch file in the 'Script' field. The affected stream's mountpoint and type of event reported ('Begin_Outage', 'End_Outage', 'Begin_Corrupted' or 'End_Corrupted') will then be passed on to the script as command line parameters (%1 and %2 on Windows systems or $1 and $2 on Unix/Linux/Mac systems) together with date and time information.

Leave the 'Script' field empty if you do not wish to use this option. An invalid path will also disable this option.

Examples for command line parameter strings passed on to the advisory 'Script' are:

FFMJ0 Begin_Outage 08-02-21 09:25:59
FFMJ0 End_Outage 08-02-21 11:36:02 Begin was 08-02-21 09:25:59

#!/bin/bash
sleep $((60*RANDOM/32767))
cat | mail -s "NABU: $1" email@address <<!
Advisory Note to BNC User,
Please note the following advisory received from BNC.
Stream: $*
Regards, BNC
!

Note the sleep command in this script which causes the system to wait for a random period of up to 60 seconds before sending the email. This should avoids overloading your mail server in case of a simultaneous failure of many streams.

This section describes a number of miscellaneous options which can be applied for a single stream (mountpoint) or for all configured streams.

Specify a mountpoint to apply one or several of the 'Miscellaneous' options to the corresponding stream. Enter 'ALL' if you want to apply these options to all configured streams. An empty option field (default) means that you don't want BNC to apply any of these options.

BNC can average latencies per stream over a certain period of GPS time, the 'Performance log' interval. Mean latencies are calculated from the individual latencies of at most one (first incoming) observation or correction to Broadcast Ephemeris per second. Note that computing correct latencies requires the clock of the host computer to be properly synchronized.

Latency: Latency is defined in BNC by the following equation:

    UTC time provided by BNC's host
  - GPS time of currently processed epoch
  + Leap seconds between UTC and GPS time
  --------------
  = Latency

Statistics: BNC counts the number of GPS seconds covered by at least one observation. It also estimates an observation rate (independent from the a priory specified 'Observation rate') from all observations received throughout the first full 'Performance log' interval. Based on this rate, BNC estimates the number of data gaps when appearing in subsequent intervals.

Latencies of observations or corrections to Broadcast Ephemeris and statistical information can be recorded in the 'Logs' canvas at the end of each 'Performance log' interval. A typical output from a 1 hour 'Performance log' interval would be:

08-03-17 15:59:47 BRUS0: Mean latency 1.47 sec, min 0.66, max 3.02, rms 0.35, 3585 epochs, 15 gaps

Select a 'Performance log' interval to activate this function or select the empty option field if you do not want BNC to log latencies and statistical information.

When configuring a GNSS receiver for RTCM stream generation, the setup interface may not provide details about RTCM message types. As reliable information concerning stream contents should be available i.e. for NTRIP broadcaster operators to maintain the broadcaster's source-table, BNC allows to scan RTCM streams for incoming message types and printout some of the contained meta-data. The idea for this option arose from 'InspectRTCM', a comprehensive stream analyzing tool written by D. Stoecker.

Tick 'Scan RTCM' to scan RTCM Version 2.x or 3.x streams and log all contained

• numbers of incoming message types
• Antenna Reference Point (ARP) coordinates
• Antenna Phase Center (APC) coordinates
• antenna height above marker
• antenna descriptor.

Note that in RTCM Version 2.x the message types 18 and 19 carry only the observables of one frequence. Hence it needs two type 18 and 19 messages per epoch to transport the observations from dual frequency receivers.

Logged time stamps refer to message reception time and allow to understand repetition rates. Enter 'ALL' if you want to log this information from all configured streams. Beware that the size of the logfile can rapidly increase depending on the number of incoming RTCM streams.

This option is primarily meant for testing and evaluation. Use it to figure out what exactly is produced by a specific GNSS receiver's configuration. An empty option field (default) means that you don't want BNC to print the message type numbers and antenna information carried in RTCM streams.

Each stream on an NTRIP broadcaster (and consequently on BNC) is defined using a unique source ID called mountpoint. An NTRIP client like BNC access the desired data stream by referring to its mountpoint. Information about streams and their mountpoints is available through the source-table maintained by the NTRIP broadcaster. Note that mountpoints could show up in BNC more than once when retrieving streams from several NTRIP broadcasters.

Streams selected for retrieval are listed under the 'Streams' canvas section on BNC's main window. The list provides the following information either extracted from source-table(s) produced by the NTRIP broadcasters or introduced by BNC's user:

'resource loader'	NTRIP broadcaster URL and port, or TCP/IP host and port, or Serial input port specification.
'mountpoint'	Mountpoint introduced by NTRIP broadcaster, or Mountpoint introduced by BNC's user.
'decoder'	Type of decoder used to handle the incoming stream content according to its format; editable.
'lat'	Approximate latitude of reference station, in degrees, north; editable if 'nmea' = 'yes'.
'long'	Approximate longitude of reference station, in degrees, east; editable if 'nmea' = 'yes'.
'nmea'	Indicates whether or not streaming needs to be initiated by BNC through sending NMEA-GGA message carrying position coordinates in 'lat' and 'long'.
'ntrip'	Selected NTRIP transport protocol version (1, 2, R, or U), or 'N' for TCP/IP streams without NTRIP, or 'UN' for UDP streams without NTRIP, or 'S' for serial input streams without NTRIP.
'bytes'	Number of bytes received.

• BNC automatically allocates one of its internal decoders to a stream based on the stream's 'format' and 'format-details' as given in the source-table. However, there might be cases where you need to override the automatic selection due to incorrect source-table for example. BNC allows users to manually select the required decoder by editing the decoder string. Double click on the 'decoder' field, enter your preferred decoder and then hit Enter. The accepted decoder strings are 'RTCM_2.x', 'RTCM_3.x', and 'RTIGS'.
• In case you need to log the raw data as is, BNC allows users to by-pass its decoders and and directly save the input in daily log files. To do this specify the decoder string as 'ZERO'. The generated file names are created from the characters of the streams mountpoints plus two-digit numbers each for year, month, and day. Example: Setting the 'decoder' string for mountpoint WTZZ0 to 'ZERO' and running BNC on March 29, 2007 would save the raw data in a file named WTZZ0_070329.
• BNC can also retrieve streams from virtual reference stations (VRS). To initiate these streams, an approximate rover position needs to be sent in NMEA format to the NTRIP broadcaster. In return, a user-specific data stream is generated, typically by a Network-RTK software. VRS streams are indicated by a 'yes' in the source-table as well as in the 'nmea' column on the 'Streams' canvas in BNC's main window. They are customized exactly to the latitude and longitude transmitted to the NTRIP broadcaster via NMEA-GGA messages.
  If NMEA-GGA messages are not coming from a serial connected GNSS rover, BNC simulates them from the default latitude and longitude of the source-table as shown in the 'lat' and 'long' columns on the 'Streams' canvas. However, in most cases you would probably want to change these defaults according to your requirement. Double-click on 'lat' and 'long' fields, enter the values you wish to send and then hit Enter. The format is in positive north latitude degrees (e.g. for northern hemisphere: 52.436, for southern hemisphere: -24.567) and eastern longitude degrees (example: 358.872 or -1.128). Only streams with a 'yes' in their 'nmea' column can be edited. The position must preferably be a point within the VRS service area of the network. RINEX files generated from these streams will contain an additional COMMENT line in the header beginning with 'NMEA' showing the 'lat' and 'long' used.
  Note that when running BNC in a Local Area Network (LAN), NMEA strings may be blocked by a proxy server, firewall or virus scanner.

To remove a stream from the 'Streams' canvas in the main window, highlight it by clicking on it and hit the 'Delete Streams' button. You can also remove multiple streams simultaneously by highlighting them using +Shift and +Ctrl.

The streams selection can be changed on-the-fly without interrupting uninvolved threads in the running BNC process.

Window mode: Hit 'Save & Activate Options' while BNC is in window mode and already processing data to let changes of your streams selection immediately become effective.

No window mode: When operating BNC online in 'no window' mode (command line option -nw), you force BNC to reread its 'mountPoints' configuration option from disk at pre-defined intervals. Select '1 min', '1 hour', or '1 day' as 'Reread configuration' option to reread the 'mountPoints' option every full minute, hour, or day. This lets a 'mountPoints' option edited in between in the configuration file become effective without terminating uninvolved threads. See annexed section 'Configuration Example' for a configuration file example and a list of other on-the-fly changeable options.

The bottom menu bar allows to add or delete streams to BNC's configuration and to start or stop it. It also provides access to BNC's online help function.

Button 'Add Streams' > 'Coming from Caster' opens a window that allows user to select data streams from an NTRIP broadcaster according to their mountpoints.

Enter the NTRIP broadcaster host IP and port number. Note that EUREF and IGS operate NTRIP broadcasters at http://www.euref-ip.net/home and http://www.igs-ip.net/home.

It may be that your are not sure about your NTRIP broadcasters host and port number or you are interested in other broadcaster installations operated elsewhere. Hit 'Show' for a table of known broadcasters maintained at www.rtcm-ntrip.org/home. A window opens which allows to select a broadcaster for stream retrieval.

Some streams on NTRIP broadcasters may be restricted. Enter a valid 'User' ID and 'Password' for access to protected streams. Accounts are usually provided per NTRIP broadcaster through a registration procedure. Register through http://igs.bkg.bund.de/index_ntrip_reg.htm for access to protected streams on www.euref-ip.net and www.igs-ip.net.

Use the 'Get Table' button to download the source-table from the NTRIP broadcaster. Pay attention to data fields 'format' and 'format-details'. Keep in mind that BNC can only decode and convert streams that come in RTCM Version 2.x, RTCM Version 3.x, or RTIGS format. RTCM Version 2.x streams must contain message types 18 and 19 or 20 and 21 while RTCM Version 3.x streams must contain GPS or SBAS message types 1002 or 1004 and may contain GLONASS message types 1010 or 1012, see data field 'format-details' for available message types and their repetition rates in brackets. Note that in order to produce RINEX Navigation files RTCM Version 3.x streams containing message types 1019 (GPS) and 1020 (GLONASS) are required. Select your streams line by line, use +Shift and +Ctrl when necessary.

The contents of data field 'nmea' tells you whether a stream retrieval needs to be initiated by BNC through sending an NMEA-GGA message carrying approximate position coordinates (virtual reference station).

Hit 'OK' to return to the main window. If you wish you can click on 'Add Streams' and repeat the process again to retrieve streams from different casters.

Some limitations and deficiencies of the NTRIP version 1 stream transport protocol are solved in NTRIP version 2. Improvements mainly concern a full HTTP compatibility in view of requirements coming from proxy servers. Version 2 is backwards compatible to Version 1. Options implemented in BNC are:

  1:  NTRIP version 1, TCP/IP.
  2:  NTRIP version 2 in TCP/IP mode.
  R:  NTRIP version 2 in RTSP/RTP mode.
  U:  NTRIP version 2 in UDP mode.

If NTRIP version 2 is supported by the broadcaster:

• Try using option '2' if your streams are otherwise blocked by a proxy server operated in front of BNC.
• Option 'R' or 'U' may be selected if latency is more important than completeness for your application. Note that the latency reduction is likely to be in the order of 0.5 sec or less. Note further that options 'R' (RTSP/RTP mode) and 'U' (UDP mode) are not accepted by proxy servers and a mobile Internet Service Provider may not support it.

Select option '1' if you are not sure whether the broadcaster supports NTRIP version 2.

Button 'Add Streams' > 'Coming from TCP/IP Port' allows to retrieve streams via TCP directly from an IP address without using the NTRIP transport protocol. For that you:

• Enter the IP address of the stream providing host.
• Enter the IP port number of the stream providing host.
• Specify a mountpoint. Recommended is a 4-character station ID. Example: FFMJ
• Specify the stream format. Available options are 'RTCM_2', 'RTCM_3', 'RTIGS', and 'ZERO'.
• Enter the approximate latitude of the stream providing rover in degrees. Example: 45.32.
• Enter the approximate longitude of the stream providing rover in degrees. Example: -15.20.

Streams directly received from a TCP/IP port show up with an 'N' for 'No NTRIP' in the 'Streams' canvas section on BNC's main window . Latitude and longitude are to be entered just for informal reasons.

Button 'Add Streams' > 'Coming from UDP Port' allows to pick up streams arriving directly at one of the local host's UDP ports without using the NTRIP transport protocol. For that you:

• Enter the local port number where the UDP stream arrives.
• Specify a mountpoint. Recommended is a 4-character station ID. Example: FFMJ
• Specify the stream format. Available options are 'RTCM_2', 'RTCM_3', 'RTIGS', and 'ZERO'.
• Enter the approximate latitude of the stream providing rover in degrees. Example: 45.32.
• Enter the approximate longitude of the stream providing rover in degrees. Example: -15.20.

Streams directly received at a UDP port show up with a 'UN' for 'UDP, No NTRIP' in the 'Streams' canvas section on BNC's main window . Latitude and longitude are to be entered just for informal reasons.

Button 'Add Streams' > 'Coming from Serial Port' allows to retrieve streams from a GNSS receiver via serial port without using the NTRIP transport protocol. For that you:

• Specify a mountpoint. Recommended is a 4-character station ID. Example: FFMJ
• Specify the stream format. Available options are 'RTCM_2', 'RTCM_3', 'RTIGS', and 'ZERO'.
• Enter the approximate latitude of the stream providing receiver in degrees. Example: 45.32.
• Enter the approximate longitude of the stream providing receiver in degrees. Example: -15.20.
• Enter the serial 'Port name' selected on your host for communication with the receiver. Valid port names are

  Windows:       COM1, COM2
  Linux:         /dev/ttyS0, /dev/ttyS1
  FreeBSD:       /dev/ttyd0, /dev/ttyd1
  Digital Unix:  /dev/tty01, /dev/tty02
  HP-UX:         /dev/tty1p0, /dev/tty2p0
  SGI/IRIX:      /dev/ttyf1, /dev/ttyf2
  SunOS/Solaris: /dev/ttya, /dev/ttyb
  

• Select a 'Baud rate' for the serial input. Note that using a high baud rate is recommended.
• Select the number of 'Data bits' for the serial input. Note that often '8' data bits are used.
• Select the 'Parity' for the serial input. Note that parity is often set to 'NONE'.
• Select the number of 'Stop bits' for the serial input. Note that often '1' stop bit is used.
• Select a 'Flow control' for the serial link. Select 'OFF' if you don't know better.

When selecting the serial communication options listed above, make sure that you pick those configured to the serial connected GNSS receiver.

Streams received from a serial connected GNSS receiver show up with an 'S' (for Serial Port, no NTRIP) in the 'Streams' canvas section on BNC's main window . Latitude and longitude are to be entered just for informal reasons.

Hit 'Start' to start retrieving, decoding, and converting GNSS data streams in real-time. Note that 'Start' generally forces BNC to begin with fresh RINEX which might overwrite existing files when necessary unless the option 'Append files' is ticked.

Hit the 'Stop' button in order to stop BNC.

Command line options are available to run BNC in 'no window' mode or let it read data from a file in offline mode. BNC will then use processing options from the configuration file. Note that the self-explaining contents of the configuration file can easily be edited. It is possible to introduce a specific configuration file name instead of using the default name 'BNC.ini'.

Apart from its regular windows mode, BNC can be started on all systems as a background/batch job with command line option '-nw'. BNC will then run in 'no window' mode, using processing options from its configuration file on disk. Terminate BNC using Windows Task Manager when running it in 'no window' mode on Windows systems.

Example:

bnc.exe -nw

Although BNC is primarily a real-time online tool, it can be run in offline mode to read data from a file for post processing purposes. Enter the following four command line options for that:

• '--file <inputFileName>' to enter the full path to an input file containing data in RTCM Version 2.x, or Version 3.x, or RTIGS/SOC format.
• '--format <format>' to enter one of the file format describing strings 'RTCM_2', 'RTCM_3' or 'RTIGS'.
• '--date YYYY-MM-DD' to enter a date for the first epoch.
• '--time HH:MM:SS' to enter a time for the first epoch.

Example:

./bnc --file FFMJ.dat --format RTCM_3 --date 2008-10-27 --time 23:12:56

Note that it is necessary to define a date and time for the first epoch because RTCM streams do not contain complete time stamps as needed for RINEX. Note further that when running BNC in offline mode, it will use options for file saving, interval, sampling etc. from its configuration file.

Example:

./bnc --conf MyConfig.ini

This leads to a BNC job using configuration file 'MyConfig.ini'. The configuration file will be saved in the current working directory.

• In Qt-based desktop environments (like KDE) on Unix/Linux platforms it may happen that you experience a crash of BNC at startup even when running the program in the background using the '-nw' option. This is a known bug most likely resulting from an incompatibility of Qt libraries in the environment and in BNC. Entering the command 'unset SESSION_MANAGER' before running BNC may help as a work-around.
• Currently BNC only handles GPS, SBAS and GLONASS data. Galileo is not yet supported.
• BNC currently will only handle C1, C2, P1, P2, L1, L2, S1, and S2 observations as well as the cumulative loss of continuity and lock time indicators. Which observables and indicators are available on a particular stream will depend on the setup of source receiver and the data format used. RTCM Version 2.x streams do not carry signal-to-noise ratio 'S' values while RTCM Version 3.x streams can only transport one code observable per frequency. Note that signal-to-noise ratios 'S' are also logged mapped to integer numbers 1 to 9.
• Using RTCM Version 3.x, BNC will properly handle message types 1002, 1004, 1010, and 1012. Note that when handling message types 1001, 1003, 1009 and 1011 where the ambiguity field is not set, the output will be no valid RINEX. All values will be stored modulo 299792.458 (speed of light).
Concerning the RTCM Version 3.x premature message types 3001-3012 (see RTCM document 012-2009-SC104-528 'Proposed SSR Messages for SV Orbit, Clock, Code Biases, URA prepared by Geo++'), a final decision is not yet made. Note the what's implemented in BNC is just a temporary solutions.
• Using RTCM Version 2.x, BNC will only handle message types 18 and 19 or 20 and 21 together with position and the antenna offset information carried in types 3 and 22. Note that processing carrier phase corrections and pseudo-range corrections contained in message types 20 and 21 needs access to broadcast ephemeris. Hence, whenever dealing with message types 20 and 21, make sure that broadcast ephemeris become available for BNC through also retrieving at least one RTCM Version 3.x stream carrying message types 1019 (GPS ephemeris) and 1020 (GLONASS ephemeris).
• Streams coming in RTIGS format carry only GPS data.
• BNC's 'Get Table' function only shows the STR records of a source-table. You can use an Internet browser to download the full source-table contents of any NTRIP broadcaster by simply entering its URL in the form of http://host:port. Data field number 8 in the NET records may provide information about where to register for an NTRIP broadcaster account.
• EUREF as well as IGS adhere to an open data policy. Streams are made available through NTRIP broadcasters at www.euref-ip.net and www.igs-ip.net free of charge to anyone for any purpose. There is no indication up until now how many users will need to be supported simultaneously. The given situation may develop in such a way that it might become difficult to serve all registered users at the same times. In cases where limited resources on the NTRIP broadcaster side (software restrictions, bandwidth limitation etc.) dictates, first priority in stream provision will be given to stream providers followed by re-broadcasting activities and real-time analysis centers while access to others might be temporarily denied.
• We experienced a limitation of the Standard Version of Microsoft Windows related to socket communication where sockets are not always handled properly. Since BNC makes intensive use of communication through sockets, we recommend to use the Server Version of Microsoft Windows when running BNC continuously for extended on a Windows platform.
• The source code provided by NRCan for decoding RTIGS streams is 32-bit dependent. Hence the BNC executable generated for 64-bit Linux systems would only run when compiled using the -m32 compiler option.
• Once BNC has been started, many of its configuration options can not be changed as long as it is stopped. See chapter 'Reread Configuration' for on-the-fly configuration exceptions.

The BKG Ntrip Client (BNC) Qt Graphic User Interface (GUI) has been developed for the Federal Agency for Cartography and Geodesy (BKG) by Leos Mervart, Czech Technical University Prague, Department of Geodesy. BNC includes the following GNU GPL software components:

• RTCM 2.x decoder, written by Oliver Montenbruck, German Space Operations Center, DLR, Oberpfaffenhofen
• RTCM 3.x decoder, written for BKG by Dirk Stoecker, Alberding GmbH, Schoenefeld
• RTIGS decoder, written by Ken MacLeod, Natural Resources, Canada.

Georg Weber
Federal Agency for Cartography and Geodesy (BKG)
Frankfurt, Germany
[euref-ip@bkg.bund.de] or [igs-ip@bkg.bund.de]

Acknowledgements
BNC's Help Contents has been proofread by Thomas Yan, University of New South Wales, Australia.
Scott Glazier, OmniSTAR Australia, included the decoding of broadcast ephemeris from RTIGS streams and has been helpful in finding BNC's bugs.
James Perlt, BKG, helped fixing bugs and redesigned BNC's main window.
Andre Hauschild, German Space Operations Center, DLR, revised the RTCMv2 decoder.
Zdenek Lukes, Czech Technical University Prague, Department of Geodesy, extended the RTCMv2 decoder to handle message types 3, 20, 21, and 22 and added loss of lock indicator.

The Radio Technical Commission for Maritime Services (RTCM) is an international non-profit scientific, professional and educational organization. Special Committees provide a forum in which governmental and non-governmental members work together to develop technical standards and consensus recommendations in regard to issues of particular concern. RTCM is engaged in the development of international standards for maritime radionavigation and radiocommunication systems. The output documents and reports prepared by RTCM Committees are published as RTCM Recommended Standards. Topics concerning Differential Global Navigation Satellite Systems (DGNSS) are handled by the Special Committee SC 104.

Personal copies of RTCM Recommended Standards can be ordered through http://www.rtcm.org/orderinfo.php.

'Networked Transport of RTCM via Internet Protocol' Version 1.0 (NTRIP) stands for an application-level protocol streaming Global Navigation Satellite System (GNSS) data over the Internet. NTRIP is a generic, stateless protocol based on the Hypertext Transfer Protocol HTTP/1.1. The HTTP objects are enhanced to GNSS data streams.

NTRIP Version 1.0 is an RTCM standard designed for disseminating differential correction data (e.g. in the RTCM-104 format) or other kinds of GNSS streaming data to stationary or mobile users over the Internet, allowing simultaneous PC, Laptop, PDA, or receiver connections to a broadcasting host. NTRIP supports wireless Internet access through Mobile IP Networks like GSM, GPRS, EDGE, or UMTS.

NTRIP is implemented in three system software components: NTRIP clients, NTRIP servers and NTRIP broadcasters. The NTRIP broadcaster is the actual HTTP server program whereas NTRIP client and NTRIP server are acting as HTTP clients.

NTRIP is an open none-proprietary protocol. Major characteristics of NTRIP's dissemination technique are:

• Based on the popular HTTP streaming standard; comparatively easy to implement when having limited client and server platform resources available.
• Application not limited to one particular plain or coded stream content; ability to distribute any kind of GNSS data.
• Potential to support mass usage; disseminating hundreds of streams simultaneously for thousands of users possible when applying modified Internet Radio broadcasting software.
• Considering security needs; stream providers and users don't necessarily get into contact, streams often not blocked by firewalls or proxy servers protecting Local Area Networks.
• Enables streaming over mobile IP networks because of using TCP/IP.

The NTRIP broadcaster maintains a source-table containing information on available NTRIP streams, networks of NTRIP streams and NTRIP broadcasters. The source-table is sent to an NTRIP client on request. Source-table records are dedicated to one of the following: Data Streams (record type STR), Casters (record type CAS), or Networks of streams (record type NET).

Source-table records of type STR contain the following data fields: 'mountpoint', 'identifier', 'format', 'format-details', 'carrier', 'nav-system', 'network', 'country', 'latitude', 'longitude', 'nmea', 'solution', 'generator', 'compr-encryp', 'authentication', 'fee', 'bitrate', 'misc'.

Source-table records of type NET contain the following data fields: 'identifiey', 'operator', 'authentication', 'fee', 'web-net', 'web-str', 'web-reg', 'misc'.

Source-table records of type CAS contain the following data fields: 'host', 'port', 'identifier', 'operator', 'nmea', 'country', 'latitude', 'longitude', 'misc'.

The major changes of NTRIP version 2.0 compared to version 1.0 are:

• cleared and fixed design problems and HTTP protocol violations;
• replaced non standard directives;
• chunked transfer encoding;
• improvements in header records;
• source-table filtering; and
• RTSP communication.

NTRIP version 2 allows to either communicate in TCP/IP mode or in RTSP/RTP mode whereas version 1 is limited to TCP/IP only.

Transmitting GNSS carrier phase data can be done through RTCM Version 2.x messages. Please note that only RTCM Version 2.2 and 2.3 streams may include GLONASS data. Messages that may be of some interest here are:

• Type 1 message is the range correction message and is the primary message in code-phase differential positioning (DGPS). It is computed in the base receiver by computing the error in the range measurement for each tracked SV.
• Type 2 message is automatically generated when a new set of satellite ephemeris is downloaded to the base receiver. It is the computed difference between the old ephemeris and the new ephemeris. Type 2 messages are used when the base station is transmitting Type 1 messages.
• Type 3 and 22 messages are the base station position and the antenna offset. Type 3 and 22 are used in RTK processing to perform antenna reduction.
• Type 6 message is a null frame filler message that is provided for data links that require continuous transmission of data, even if there are no corrections to send. As many Type 6 messages are sent as required to fill in the gap between two correction messages (type 1). Message 6 is not sent in burst mode.
• Type 9 message serves the same purpose as Type 1, but does not require a complete satellite set. As a result, Type 9 messages require a more stable clock than a station transmitting Type 1 's, because the satellite corrections have different time references.
• Type 16 message is simply a text message entered by the user that is transmitted from the base station to the rover. It is used with code-phase differential.
• Type 18 and 20 messages are RTK uncorrected carrier phase data and carrier phase corrections.
• Type 19 and 21 messages are the uncorrected pseudo-range measurements and pseudo-range corrections used in RTK.
• Type 23 message provides the information on the antenna type used on the reference station.
• Type 24 message carries the coordinates of the installed antenna's ARP in the GNSS coordinate system coordinates.

RTCM Version 3.x has been developed as a more efficient alternative to RTCM Version 2.x. Service providers and vendors have asked for a standard that would be more efficient, easy to use, and more easily adaptable to new situations. The main complaint was that the Version 2 parity scheme was wasteful of bandwidth. Another complaint was that the parity is not independent from word to word. Still another was that even with so many bits devoted to parity, the actual integrity of the message was not as high as it should be. Plus, 30-bit words are awkward to handle. The Version 3.x standard is intended to correct these weaknesses.

RTCM Version 3.x defines a number of message types. Messages that may be of interest here are:

• Type 1001, GPS L1 code and phase.
• Type 1002, GPS L1 code and phase and ambiguities and carrier to noise ratio.
• Type 1003, GPS L1 and L2 code and phase.
• Type 1004, GPS L1 and L2 code and phase and ambiguities and carrier to noise ratio.
• Type 1005, Station coordinates XZY for antenna reference point.
• Type 1006, Station coordinates XYZ for antenna reference point and antenna height.
• Type 1007, Antenna descriptor and ID.
• Type 1008, Antenna serial number.
• Type 1009, GLONASS L1 code and phase.
• Type 1010, GLONASS L1 code and phase and ambiguities and carrier to noise ratio.
• Type 1011, GLONASS L1 and L2 code and phase.
• Type 1012, GLONASS L1 and L2 code and phase and ambiguities and carrier to noise ratio.
• Type 1013, Modified julian date, leap second, configured message types and interval.
• Type 1014 and 1017, Network RTK (MAK) messages (under development).
• Type 1019, GPS ephemeris.
• Type 1020, GLONASS ephemeris.
• Type 4088 and 4095, Proprietary messages (under development).

RTIGS stands for a data format and transport protocol for GPS observations. It was defined by the Real-Time IGS Working Group (RTIGS WG). Its definition is based on the SOC format. Every RTIGS record has one of the following numbers:

Station record number 100
Observation record (O_T) number 200
Ephemeris record (E_T) number 300
Meteorological record (M_T) number 400

Every station has one of the following unique numbers:

1-99 reserved for JPL
100-199 reserved for NRCan
200-299 reserved for NGS
300-399 reserved for ESOC
400-499 reserved for GFZ
500-599 reserved for BKG
600-699 reserved for GEOSCIENCE AUS
700-799 others
etc

The number of bytes in each real time message includes the header as well as the data content, but NOT the pointer.

For example:

• A station message is output once per hour and is 20 bytes.
• An observation message is output once per second. The header is 12 bytes long and the SOC data is 21 bytes per PRN. So a typical RTIGSO_T message will be 390 bytes if 8 sats are being tracked.
• An ephemeris message is output when the ephemeris is decoded by the GPS receiver. The time in the ephemeris header is the collected time. Only one ephemeris can be bundled in a RTIGSE_T message.
  A RTIGSE_T message contains one eph. The message consists of 12 header bytes and 72 ephemeris bytes, for a total of 84 bytes.
• The RTIGSM_T (met) message should be issued once every 15 minutes. A basic met message consists of a 12 byte header and 3 longs (temp, press and relative humidity) for a total of 24 bytes.

All records are related to a station configuration indicated by the Issue of Data Station (IODS). The IODS will enable the user to identify the equipment and software that was used to derive the observation data.

Each record header contains the GPS Time in seconds which flows continuously from 6 Jan-1980 onwards.

The data payload of each record consists of observations. The structures indicate a pointer to data but in fact the broadcast messages do not contain the pointer, only the data. Users will have to manage the data and the pointer is shown in order to illustrate where the data is located in the message and one possible data management option.

All record data are in network byte order (Big Endian), i.e. IA32 users have to swap bytes.

Visit http://igscb.jpl.nasa.gov/mail/igs-rtwg/2004/msg00001.html for further details.

The SOC format has been designed in July 1999 by the Jet Propulsion Laboratory (JPL) and the California Institute of Technology (CalTech) to transport 1Hz GPS data with minimal bandwidth over the open Internet. SOC follows the 'little-endian' byte order meaning that the low-order byte of a number is stored in memory at the lowest address, and the high-order byte at the highest address. Because the transport layer is UDP, the format does not include sync bits, a checksum, or cyclic redundancy checksum (CRC). SOC allows to transport the GPS observable CA, P1, P2, L1, and L2, efficiently compressed down to 14 bytes with 1 mm range resolution and 0.02 mm phase resolution. SOC contains epochs for cycle slips, a stand-alone time-tag per epoch, a minimum representation of the receiver's clock solution, 3 SNR numbers, a unique site id, a modulo 12 hour sequence number and flags for receiver type and GPS health. SOC's simple structure comprises an 8 byte header, a 9 byte overhead for timetag, number of gps, etc., plus 21 data bytes per gps.

Visit http://gipsy.jpl.nasa.gov/igdg/papers/SOC_FORMAT.ppt for further details.

The following table's left column is an example for the contents of a configuration file 'BNC.ini'. It enables the retrieval of stream ACOR0 form www.euref-ip.net for the generation of 15 min RINEX files. RINEX files are uploaded to an archive using script 'up2archive' :

Note that the following configuration options saved on disk can be changed/edited on-the-fly while BNC is already processing data:

• 'mountPoints' to change the selection of streams to be processed, see section 'Streams',
• 'waitTime' to change the 'Wait for full epoch' option, see section 'Feed Engine', and
• 'binSampl' to change the 'Sampling' option, see section 'Feed Engine'.