Terminal Server - Modern Usage

Modern Usage

A "terminal server" is used many ways but from a basic sense if a user has a serial device and they need to move data over the LAN, this is the product they need.

• Raw TCP socket connection: A raw TCP socket connection which can be initiated from the terminal server or from the remote host/server. This can be point-to-point or shared, where serial devices (like card readers, scanners, bar code readers, weight scales, etc.) can be shared amongst multiple devices. TCP sessions can be initiated from the TCP server application or from the terminal server.

• Raw UDP socket connection: For use with UDP based applications, terminal servers can convert serial equipment data for transport across UDP packets on a point-to-point basis or shared across multiple devices.

• Console management - reverse Telnet, reverse SSH: In console management terminology, users can use reverse Telnet or SSH to connect to a serial device. They run Telnet or SSH on their client (PC) and attach to the terminal server, then connect to the serial device. In this application, terminal servers are also called console servers because they are used to connect to console ports which are found on products like routers, PBXes, switches and servers (Linux or Sun). The idea is to gain access to those devices via their console port.

• Connect serial-based applications with a COM/TTY port driver: Many software applications have been written to communicate with devices that are directly connected to a server's serial COM ports (robotic assembly machines, scanners, card readers, sensors, blood analyzers, etc.). Companies may want to network these applications because the devices that were directly connected to the server's COM ports need to be moved to a location some distance away from the application server. Since the original application was designed to talk directly to a specific COM port, a solution seamless to both the application and device must be implemented to enable communication across an IP network. I.e. a solution that makes the application think it is talking directly to a COM port. In this application, serial ports can be connected to network servers or workstations running COM port redirector software operating as a virtual COM port. Many terminal server vendors include COM port redirector software with their terminal servers. This application need is most common in Windows environments, but also exists in Linux and Unix environments.

• Serial tunneling between two serial devices: Serial tunneling enables users to establish a link across Ethernet to a serial port on another terminal server.

• Back to back: This application is designed to solve a wiring problem. For example, a user needs to replace RS-232, RS-422 or RS-485 wire and run their data over Ethernet without making any changes to the server or the ultimate serial device, a user wants to replace a parallel leased line modem network with their parallel Ethernet network, or someone has a pick and place machine that puts ICs on boards, and they want to move the server into a back room where the equipment will be safe from damage. This application is ideal where a device exists with an application written to gather information from that device (common with sensors). This application allows them to eliminate the wiring. It can be also be used with industrial devices (Allen-Bradley, Siemens, Modbus) so that those devices can be run transparently across the network.

• Virtual modem: Virtual modem is another example of a back-to-back application. It may be used to replace modems but still use an AT command set. An IP address is typed into the AT command set instead of the phone number of a serial device.