DATA CHECKED OCT 2026

NTRIP explained: caster, mount point, port and login

The five boxes every RTKReal-time kinematic. A way to make GPS accurate to about an inch by getting live corrections from a nearby base station.More app asks you to fill in, and what each one means.

NTRIPThe standard way RTK corrections are sent over the internet. Think of it as internet radio for correction data.More is the standard way RTK CorrectionsLive info from a base station about how far off the satellite signals are, so your rover can cancel out the error.More travel over the internet. The name stands for Networked Transport of RTCMThe common format RTK corrections are written in, so different brands can understand each other.More via Internet Protocol. RTCM is just the common format the corrections are written in.

BKG, the German agency that helped create NTRIP, says it has three parts:

  • Servers send data from the Base stationA GNSS receiver sitting still on a known spot. It figures out how wrong the satellite signals are right now and shares that as corrections.More.
  • A CasterThe internet server that hands out correction streams. Your rover logs in to it, like tuning into a radio station.More collects it and hands it out. Think of it as a radio station tower.
  • Clients receive it. Your RoverThe receiver that moves around the job, like a survey pole or a drone. It uses the base's corrections to find its exact spot.More or drone controller is the client, like a radio tuned to one channel.
Reference stationNTRIP server Casterhost : port (often 2101)mount pointsuser / password Your rover / RCNTRIP client RTCM ▶RTCM ▶◀ GGA position(for VRS / nearest)
NTRIP flow.
Illustrative diagram by FixFinder, not to scale.

The boxes you fill in

Caster host
The server's address. It looks like a web address or a string of numbers.
Port
Which "door" on the server to use. It is very often 2101, but use whatever your provider tells you.
Mount pointOne specific correction stream on a caster, like one channel on a radio. Each one comes from a certain station or network setup.More
The channel you tune to. It might be one station, the nearest station, or a VRSVirtual reference station. The network blends nearby stations to create a pretend base right next to you, which keeps the baseline short.More (a "virtual" station made just for you). Each channel has its own format, such as RTCM 3 MSMMultiple Signal Messages. A newer kind of RTCM 3 message that carries all satellite systems and signals.More, and its own list of satellite systems.
Username and password
Your login from the network. Even free state networks usually make you sign up.

SourcetableThe list of every mount point a caster offers. Your app shows it when you connect without picking one.More: if you connect without picking a mount point, the caster sends back a list of every channel it has. Many apps show this as a drop-down menu.

GGAA short message your rover sends with its rough location. VRS and nearest-station streams need it to know where you are.More: VRS and "nearest station" channels need to know roughly where you are. Your rover tells them by sending a short message called an NMEAA common text format GPS receivers use to report position and status. GGA is one NMEA message.More GGA sentence. If a VRS channel sends you nothing, check that GGA is turned on.

Each state page lists the network's caster host and PortA number that tells your device which "door" on the caster server to use. For NTRIP it's often 2101.More when the network publishes them. Start from the state map, then follow the receiver setup guides.

Sources (checked Oct 16, 2026):BKG: NTRIP aboutEmlid NTRIP CasterEmlid Reach RS3 docs: RTK quickstartDiagrams are FixFinder illustrations. Always follow your equipment's current manual.

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