NTRIP and RTCM – how RTK corrections travel
How RTK corrections travel over the internet: NTRIP caster, mountpoint and sourcetable, sending GGA, NTRIP v1/v2 and the RTCM 3 MSM messages of our bases.
NTRIP (Networked Transport of RTCM via Internet Protocol) is the standard protocol for delivering RTK corrections over the internet. It defines three roles:
- NTRIP server / source – the base station that sends corrections.
- NTRIP caster – the server (in our case
rtk.ba) that receives corrections from all base stations and distributes them to authorised users. - NTRIP client – your rover/terminal/application.
Mountpoint and sourcetable
A mountpoint is the name of a single correction stream. When a client asks the caster for the list, it receives the sourcetable – a catalogue of mountpoints with their format and approximate location. On RTK.ba we recommend AUTO: the gateway selects the nearest base station from your position automatically.
GGA – why the receiver reports its position
For AUTO to know which base station is nearest to you, the receiver must periodically send its approximate position as an NMEA $GPGGA/$GNGGA sentence. In most terminals this is an option called "Send GGA", "NMEA GGA upload" or "VRS mode" – enable it (interval 1–10 s).
NTRIP v1 and v2
We support both versions. If your device offers a choice and you are not sure – select v1 (widest compatibility) or leave it on automatic.
RTCM 3 messages
Corrections use the binary RTCM 3.x standard. Our base stations broadcast MSM messages for all four constellations:
| Message | Content |
|---|---|
| 1005 | Base station antenna reference point (ARP) position |
| 1074 | GPS MSM4 observations |
| 1084 | GLONASS MSM4 observations |
| 1094 | Galileo MSM4 observations |
| 1124 | BeiDou MSM4 observations |
| 1230 | GLONASS code-phase biases |
Bandwidth is modest: about 0.5–1 KB/s, i.e. ~2–4 MB per hour of operation.
Related: Ready to set up? Follow connecting to RTK.ba via NTRIP step by step. If your receiver does not get FIX, see troubleshooting.