Using TCP-Com as a software-based Terminal Server with a wireless CDPD Modem to collect remote GPS survey information over the Internet.

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 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.

TCP-Com Benefits

• TCP-Com allows multiple 5700 ROVER units to be connected to one BASE. It can do this as it allows connections from multiple TCP/IP clients simultaneously.
• This makes it possible to perform surveys in multiple locations simultaneously.
• With TCP-Com's and the Survey Controller's ability to communicate over TCP/IP survey data can be collected in real-time from anywhere where a cell phone can be used to call up the CDPD carrier and communicate over the Internet.
• TCP-Com is cost effective and very easy to set up and use.

Conclusion

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.

Read the full technical details of this application. (2.5 MB Word Document)