Ntrip - Networked Transport of RTCM via Internet Protocol

Ntrip stands for an application-level protocol for streaming Global Navigation Satellite System (GNSS) data over the Internet.
It is a generic, stateless protocol based on the Hypertext Transfer Protocol HTTP/1.1. The HTTP objects are enhanced to GNSS data streams. Ntrip 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. It supports wireless Internet access through Mobile IP Networks like GSM, GPRS, EDGE, or UMTS.

Ntrip is implemented in three system software components: NtripClients, NtripServers and NtripCasters. The NtripCaster is the actual HTTP server program whereas NtripClient and NtripServer are acting as HTTP clients.

Ntrip is meant to be an open none-proprietary protocol. Major characteristics of Ntrip 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 up to thousand users possible when applying modified Internet Radio broadcasting software.
• Considering security needs; stream providers and users do not necessarily get into contact, streams often not blocked by firewalls or proxyservers protecting Local Area Networks.
• Enables streaming over any mobile IP network because of using TCP/IP.

Motivation

Since 1993 the RINEX Format is the standard file format for long-time storage and dissemination of GNSS receiver data, targeted mainly for the estimation of station coordinates in post-processing mode. RINEX data can be downloaded at several global and regional data centers usually as "daily" files containing 24 hours of data.
With ongoing development and the desire for getting information immediately the demand for accessing GNSS data with very small delay (in real-time) grew. Monitoring and of course positioning are probably the main use cases where real-time data is indispensable.
In order to disseminate GNSS data in real-time a new format had to be developed. RTCM messages (see RTCM Home Page) are nowadays widely used for this purpose. In addition to a format a transport protocol had to be defined, the so-called Ntrip streaming protocol, developed at BKG together with TU Dortmund. Using this protocol the data user is able to communicate with the data provider. Georg Weber, the former scientific director in the Department of Geodesy at BKG and representing BKG as a member of the RTCM Services Special Committee (SC) 104 played a decisive role in the development and promotion of real-time GNSS and Ntrip.
An important reason why Ntrip has been widely accepted is that BKG provides software tools for both, the server and the client side. On the server side the BKG Ntrip Broadcaster was developed to stream GNSS data in real-time over the Internet. The BKG Ntrip Client (BNC), which is not only an Ntrip client, is the leading internationally accepted standard Ntrip client application. It's development started in 2005 mainly by Leos Mervart from TU Prague.

Documentation

The material provided here describes the Ntrip real-time GNSS data transport protocol definition and the description of an Ntrip Example Implementation. Note that the protocol definition made available here is not the official Ntrip documentation. The standards can be purchased at the RTCM shop.
The Ntrip working group of RTCM SC104 provides a practical guidance to developers of Ntrip client software. The document is distributed freely at the RTCM shop. New

Ntrip, Version 1.0

In September 2004 Ntrip Version 1.0 became an RTCM Recommended Standard, see Press Release. The Transport Protocol Definition Vers. 1.0, Status 2004-09-30 is available here.

Ntrip, Version 2.0

In June 2009 RTCM Special Committee 104 (SC104) has completed a Version 2.0 of its Ntrip standard, see Press Release. Major changes compared to Version 1.0 are:

• Cleared and fixed design problems and HTTP protocol violations
• Replaced non standard directives
• Adds chunked transfer encoding
• Improves header records
• Provides for sourcetable filtering
• Provides for Real Time Streaming Protocol (RTSP) communication

Note that Ntrip Version 2.0 is fully downward compatible with Ntrip Version 1.0.

Ntrip Broadcaster

Global Navigation Satellite System (GNSS) data can be broadcast in real-time over the Internet using the Ntrip dissemination technique. In this context, the purpose of so-called Ntrip Broadcasters is to split data streams coming in from GNSS Reference Stations (Sources) for many simultaneously listening Clients. Ntrip Broadcasters do not alter the data. The communication between Sources, a Broadcaster, and its Clients is done through HTTP. Ntrip supports the dissemination of any GNSS data stream (GPS, GLONASS, Galileo, EGNOS, WAAS etc.) that needs 0.2 to 10 Kbit/s transmission rate and carries e.g.

• RTCM observations or broadcast ephemeris or orbit/clock corrections, DGPS, RTK
• RTCA corrections, EGNOS & WAAS
• Raw receiver data, vendor formats
• RINEX observations
• BINEX observations
• other GNSS data/formats

Ntrip Broadcasters are currently installed world-wide to disseminate GNSS data in real-time. Visit www.rtcm-ntrip.org for a list of known installations.

BKG maintains the following Ntrip Broadcasters:

Visit our stream list to get more details. See here for a more comprehensive list of Ntrip Broadcasters dedicated to support IGS and EUREF.

BKG offers the BKG Professional NtripCaster SW for disseminating GNSS real-time data streams via Internet. Read more »

Access

To get access to BKG casters please use our registration page.

Use Cases

The user registration for access to the GNSS streams requires a short description of the user's real-time application. To see a selection of anonymized application descriptions, click here.

Ntrip References

The following links shall provide some background information on Ntrip usage and further Ntrip development. We try to keep the list up to date. Feel free to inform us about your Ntrip publication in case you would like to see it listed below.

Ntrip: Protocol, Video on YouTube,English
Ntrip: Client Excercise, Video on YouTube, English
Ntrip: Application and Benefit in Modern Surveying Systems, English
Nutzung der Internet-Radio-Technologie zur Übertragung von GNSS-Daten, German
Die Zukunft spricht Ntrip, German
El proyecto EUREF-IP: Resultados con GPRS, Spanish
Techniques GPS-RTK appliquées à la trajectographie, French
GNSS-Echtzeitorbitkontrolle auf Basis Internet-transferierter ..., German
D-GNSS Accuracy Test At Bucu EPN Station, English
Networked Transport of RTCM via Internet Protocol, English
Ntrip: PP-Presentation, IAG, Sapporo, Japan, 2003, English
Новый формат Ntrip передачи..., Russian
Test Results of an Internet RTK System Based on the Ntrip Protocol, English
Ntrip - Ein neues Konzept zur Übertragung von Korrekturdaten unter SAPOS, German
Benefits of Telecommunications Technology to GPS Users, English
GNSS/GPS infrastructure to support LBS Positioning Systems in Victoria, English
NTRIP Estudi i Aplicacions, Catalan
Interactive Map of EUREF-IP Real-Time GNSS Data Streams, English
Verbesserte GPS-Positionsschätzung mit IP-transportierten ..., German

Data and Products

Real-time observations, ephemeris and corrections can be received from following non-exhaustive list of Ntrip Broadcasters. Corrections are disseminated in the RTCM-State Space Representation (RTCM-SSR) format that has been adopted by the IGS and can be used for real-time PPP.

Observations

For the very beginning real-time observations have been made available on IGS and EUREF broadcasters in form of legacy messages for GPS and GLONASS (1004, 1012). Nowadays they have been more and more replaced by the new RTCM3 Multi-Signal Message (MSM) format that was developed to handle all GNSS constellations, signals, and observation types.

Broadcast Ephemeris

Several Ntrip broadcasters disseminate streams carrying only broadcast ephemeris. They derive their stream contents independently from a globally distributed selection of mainly EUREF and IGS reference stations. Ephemeris message repetition rates vary between 1 and 5 seconds.

Broadcast Ephemeris messages from globally distributed streams are also converted to RINEX Navigation files. These files are made available for download at https://igs.bkg.bund.de/root_ftp/NTRIP/BRDC/. Unlike daily concatenated files from reference stations, their 24h sliding window content is updated every 15 minutes.

Broadcast Orbit and Clock Corrections

Precise orbits and clocks can be derived from corrections to Broadcast Ephemeris. RTCM's State Space Representation (SSR) Working Group has developed appropriate v3 messages to disseminate such Broadcast Corrections in real-time. The following messages are defined:

Orbit corrections are provided in along-track, cross-track and radial components. These components are defined in the earth-centered, earth-fixed reference frame of the broadcast ephemeris. Clock corrections are not adjusted for the 2nd-order relativistic effect. After applying corrections, the satellite position and clock is referred to the 'ionospheric free' phase center of the antenna which is compatible with the broadcast orbit reference. The orbit and clock corrections do neither include local effects (like Ocean Loading or Solid Earth Tides) nor atmospheric effects (ionosphere and/or troposphere). There is currently no RTCM SSR message for ionospheric state parameters. The development of ionospheric messages will be the next step in the schedule of the RTCM State Space Representation Working Group.

Products naming convention

At the end of the year 2019 a new naming convention for real-time products was introduced by the IGS Real-time working group. According to that the mountpoints should have the pattern "TTTTXXAAAF" with

TTTT

stream type (SSRA, SSRC, IONO, BCEP, etc.)

XX

2 digit solution ID

AAA

3 letter agency code

F

1 digit format ID (0: RTCM3, 1: IGS-SSR, 2-9: reserved)

The stream type (TTTT) can be one of the following:

SSRA

state space correction stream (orbits, clocks, ...), orbits refer to APC. Example: SSRA01BKG0 (former CLK11)

SSRC

state space correction stream (orbits, clocks, ...), orbits refer to COM. Example: SSRC01BKG0 (former CLK01)

DCBS

state space correction stream (DCBs only)

IONO

ionospheric correction stream

TROP

tropospheric correction stream

BCEP

broadcast navigation data (ephemeris) stream

Note that SSRA and SSRC may also contain DCBs, iono corrections, tropo corrections and phase-bias corrections.
A transition table from short to the new long mountpoint names is available here.

Broadcast Correction IDs

Any RTCM Version 3 Broadcast Correction stream contains three types of IDs to identify its contents.

• A globally unique SSR Provider ID (PID) released by RTCM to identify a SSR service, see SSRProvider.
• A SSR Solution ID (SID) which indicates different SSR services of one SSR provider.
• A Issue Of Data (IOD) to indicate a change in the SSR generation, which may be relevant for rover operation.

The following are IDs used in IGS and EUREF context:

Based on the SSR messages defined by RTCM, the streams on products.igs-ip.net are made available as a common effort of EUREF and IGS.

RTCM SC-104 Messages for real-time GNSS applications

A selection of message types defined in RTCM v3:

Abbreviations:

RTK

Real-Time Kinematic

SSR

State Space Representation

MSM

Multiple Signal Message

URA

User Range Accuracy

HR

High-rate Clock Corrections to Broadcast Ephemerides

MSM Description:

MSM1

Compact Pseudoranges

MSM2

Compact PhaseRanges

MSM3

Compact Pseudoranges and PhaseRanges

MSM4

Full Pseudoranges and PhaseRanges plus CNR

MSM5

Full Pseudoranges, PhaseRanges, PhaseRangeRate and CNR

MSM6

Full Pseudoranges and PhaseRanges plus CNR (high resolution)

MSM7

Full Pseudoranges, PhaseRanges, PhaseRangeRate and CNR (high resolution)

Links:

• Status of RTCM Version 3 message implementation in BNC
• RTCM Home Page
• software.rtcm-ntrip.org
• SNIP RTCM 3 message cheat sheet
• RTKLIB supported RTCM 3 messages types

Monitoring

The operation of a real-time GNSS service demands a much higher level of monitoring than it is necessary in the post-processing world, where for example RINEX files can be reprocessed the next day in case of an error. Some monitoring tools and status pages are listed below.

NABU's

The Broadcaster function is continuously monitored by an alarm system that generates "Notice Advisories to Broadcaster Users", in short NABU's. If a data stream is unavailable for several minutes due to any reason, the monitor system generates a NABU message and sends it by e-mail to the affected stream provider. An additional message is sent when the stream becomes available again. All NABU messages are stored in the NABU's Archive.

In addition availability and status information are available for IGS and EPN broadcasters.

PPP (Precise Point Positioning)

BKG continuously generates PPP Plots which present results from BNC-PPP jobs run either non-stop or with consecutive hourly restarts. They are meant for test and evaluation purposes and show the performance in terms of coordinate displacements. The mainly used PPP client program is BNC which is capable of handling Broadcast Ephemeris Corrections for satellite orbits and clocks coming in RTCM v3 format.
The intention is to give a rough idea on the real-time accuracy you may expect when using BNC with orbit and clock correction streams derived from the global IGS real-time networks. Note that your results may be less or more accurate depending on current satellite coverage. Problems may be caused by deficiencies of orbit/clock correctors, deficiencies of the BNC software, or by outages in the stream flow over the Internet.

Software

Beside the BKG Ntrip Client and BKG Ntrip Caster some further Ntrip related tools and software are listed in the following non-exhaustive table:

Online tools

• SNIP NTRIP Caster Table Checker