Sharing One Trimble GPS Base Station with Multiple Rovers over the Internet
Summary: Trimble’s GPS Total Station 5700 survey system pairs base stations with field rovers — but the cellular modems linking them couldn’t support multiple simultaneous connections. TCP-Com from TALtech solved it as a software-based terminal server: the 5700 BASE’s RS232 data stream becomes available over any TCP/IP network, letting multiple rovers in multiple locations survey from a single base at the same time.
The Challenge
Survey crews often need several rovers working simultaneously off one base station’s correction stream. The 5700 BASE outputs its data over RS232, and rovers connected over cellular packet-data modems and the Internet — but the host modem could support only a single TCP session, limiting each base to one rover and forcing crews to deploy redundant base stations for multi-site work.
The Solution
TCP-Com runs on a Windows PC connected to the 5700 BASE’s serial port and acts exactly like a hardware terminal server, in software: serial data in, TCP/IP out. Configured as a TCP server on the PC’s public IP address, with multiple client connections enabled and inbound serial data broadcast to all clients, TCP-Com makes the base station’s stream available to every rover that connects — each rover’s controller simply dials the server’s IP address and port instead of a phone number. Once connected, every rover receives the base data simultaneously, from anywhere with an Internet connection, and surveys proceed normally in multiple locations at once.
The Results
- Multiple 5700 rovers served by one base station simultaneously
- Surveys running in multiple locations at the same time from shared corrections
- Rovers connect from anywhere both ends have Internet connectivity
- A software solution replacing dedicated terminal-server hardware
How You’d Set This Up Today
The cellular network of the original deployment has long since given way to LTE and 5G IP modems — which makes this architecture more relevant, not less, since every modern cellular modem is natively an Internet device. TCP-Com on current Windows 10/11 performs the same role for any RS232, USB, or networked serial instrument: one physical device, many simultaneous network clients. Surveyors, SCADA integrators, and telemetry systems use it to share GPS corrections, weather stations, and monitoring instruments across sites — and TCP-Com’s virtual COM port mode also works the other direction, making remote networked devices appear as local COM ports to legacy software.
Collecting Data from Your Own Instruments?
Need one serial device available to many computers — or a networked device visible as a COM port? Download a free TCP-Com trial or call (800) 722-6004 and we’ll map out your configuration together.
Originally published in our application archives · Updated August 2026
Additional Legacy Notes from this Case Study:
Trimble is a leading innovator of Global Positioning System (GPS) technology. Trimble manufactures an integrated GPS survey system called a GPS Total Station 5700. This is used in remote sites like this to collect survey information and the information can be automatically transmitted from a 5700 ROVER to a 5700 BASE station using an AirLink Raven II CDPD (Cellular Packet Data) Modem and a “Wireless IP” service.
AirLink is a leading provider of wireless connectivity products for remote devices enabling real-time data collection. The CDPD Raven II modem is designed for commercial applications and is the perfect choice for Telemetry, SCADA, AVL/Dispatch and Public Safety applications with its rugged industrial design. It is sometimes necessary to connect multiple 5700 ROVERS to one 5700 BASE simultaneously. The Host CDPD Modem cannot support multiple simultaneous TCP sessions. However, by using TCP-Com from TALtech as a software-based terminal server it is possible for multiple Trimble 5700 ROVERS to communicate over AirLink CDPD Modems and the Internet.
Using TCP-Com, you can attach a DGPS server such as the 5700 BASE (or any other RS232 device) to the serial port of a Windows® PC and have that data available anywhere over any TCP/IP based network – including the Internet. Given that CDPD networks are all connected to the Internet, connecting a 5700 BASE to a PC with an Internet connection running TCP-Com can make that data available to any 5700 ROVERS equipped with CDPD Modems.
TCP-Com can be described as a software-based terminal server. Much like a physical terminal server, TCP-Com acts as middleware lying in-between a physical serial port and a TCP/IP network. Data that comes into the serial port is passed to connections made to the TCP side. TCP-Com can accept connections from multiple TCP clients, allowing data from a device connected to the serial port to be sent to more than one client at the same time. In this case, the clients for TCP-Com are handheld Trimble Survey Controllers with the 5700 ROVERS.
TCP-Com Set Up
TCP-Com is set up with the serial port settings matching those of the 5700 BASE. It is set up as a TCP Server with the IP address as the Public IP Address. The TCP port can be set to any number. It is also set up to allow multiple client connections to allow multiple ROVERS to connect to a single BASE. Then the setting to send inbound serial data to all TCP/IP clients is selected as this is the key to distributing the RS232 data from the 5700 BASE to every 5700 ROVER. Once TCP-Com is activated it is then possible to connect to it from anywhere on the CDPD network or the Internet. As soon as a successful connection is made from any remote ROVER via CDPD this is displayed in TCP-Com.
5700 ROVER Connection via CDPD to TCP-Com
The ROVER controller should be configured using a cellular modem, however instead of dialing a phone number it dials an IP address and TCP Port – specifically those of the TCP-Com server, i.e., 166.148.11.123/12345 where the first part is the IP address followed by a “/” and the port number (here 12345)
Once the ROVER survey controller is started it is necessary to set the ROVER radio as a Cellular Modem (under “Radio Type”).
5700 BASE is just set up to communicate with the PC running TCP-com via its RS232 connection. Once connected, the 5700 BASE will be transmitting data into the serial port of the PC. TCP-Com will listen on the Com Port for the data, taking it and passing it into the TCP stack. The data is then made available to any ROVER making a TCP connection to the TCP-Com server. Once the Trimble Survey Controller at the 5700 BASE is powered up the survey can be started and data will be sent to the TCP-Com server. Then all the Trimble Survey Controllers with the 5700 ROVERS can be powered up to communicate via the ROVER CDPD Modem. Once the survey is started the TCP-Com server is dialed as described above and the connection is made. Once connected, data will be passing from out of the PC (running TCP-Com) over the TCP connection to the ROVERs. Each ROVER will indicate on its screen that it is in fact receiving data from the BASE. At this point, any of the survey operations can be performed.
The combination of the Trimble GPS Total Station 5700, an AirLink Raven II CDPD Modem and TCP-Com allows survey information to be collected in real-time from many remote survey sites.