ntrip

1. NGS Real Time Network
Status & Future Prospects
Neil Weston
NGS Convocation, 2005
Silver Spring, MD

2. Main Concepts
• Modify CORS sites for real time data
transmission
• GPS receiver data
• Transmission via the Internet
• Standardized protocols and formats
• Not a navigation service!

3. CORS Site Modification
• Receiver modifications
– Firmware
– Multiple satellite systems
– Data interval
• Communications / Network modifications
– Routers
– Increased bandwidth
– Internet
• Software

4. Network Design Issues
• What format?
• What stations?
• What software?
• What distance?
• What data rate?
• What latency?

5. Formats
• RTCM-SC104
– Versions – 2.0, 2.1, 2.2, 3.0
– Type 1 Fixed GPS corrections (1 sec)
– Type 3 GPS reference station parameters (10)
– Type 16 GPS special message (30,60)
– Type 18 RTK uncorrected carrier phases (1)
– Type 19 RTK uncorrected pseudoranges (1)
– Type 22 Extended station parameters (15)
– Type 59 Proprietary messages (1)

6. Formats cont.
• Raw
– Topcon/Javad Compact (1)
– Ashtech MBEN (5) / PBEN (5) / SNAV
– Thales ASCII
– SP3 ASCII
– Trimble RT17, concise
– Leica LB2
– RINEX
– BINEX

7. CORS Stations
• NDGPS
• WAAS
• PBO Network
• Other contributors sites

8. Software
• NTRIP - Networked Transport of RTCM via Internet
Protocol (version 1.5)
• NTRIP is an RTCM standard
• Application-level protocol streaming Global
Navigation Satellite System (GNSS) data over the
Internet
• Based on hypertext transfer protocol (HTTP/1.1)
• Simultaneous connections from PC’s, laptops,
receivers to a broadcast host
• Streams data to stationary and mobile users

9. Software cont.
• NTRIP – Three major components
– NtripClients – acts as an HTTP client
– NtripServers – acts as an HTTP client
– NtripCasters – HTTP server

12. DGPS/ RTK Data Rates
• DGPS – 0.5 kbits/sec
• RTK – 5 kbits/sec
• Much less demanding than Internet radio,
teleconferencing … 128 kbits/sec …

13. Administration of NtripCaster
• Logs
• Sourcetable
• Configuration file
• User registration

14. NTRIP Pros / Cons
• RTCM standard
• Open documentation
• Software components developed under GNU General
Public License
• Communications through a HTTP port
• Workload on server side
• Not supported by mobile IP provider

15. Data Rate / Latency
• Modified CORS Stations – 1 second interval
• Latency – Not more than 1 to 2 seconds
• Most third party software packages buffer the data
before processing begins

16. NTRIP Consequences
• Easy to become a provider
• Drivers available for real time software development
• End of special hardware for receiving RTCM / RTCA
• Support for networking software
• Lots of potential for mass-usage
• Sites, networks and coverage will grow
• Many third party client and server applications
already exist

17. NTRIP Demonstrations
www.euref-ip.net:2101
– RTK station
– RINEX test station
– Erlanger
alt.ngs.noaa.gov:2101
– NGS_GRD
– NGS_LAB
How you can listen

18. Conclusion
• Streaming GNSS data over the Internet is feasible
• No significant lack of performance compared to other
transportation media
• Advantages for user / service providers
• Developments for various products
• Promising solution for GIS
• Faster data access

19. References
• NTRIP BKG – GPS/GLONASS Data Center
– http://igs.ifag.de/index_ntrip.htm
• RTCM – Radio Technical Commission for Maritime
Services
– http://www.rtcm.org