Data Comm for Business, Inc.

Using the Etherpath with PC and Unix Port Redirection

In addition to its most common use as a "nailed-up RS-232 pipe" when used in pairs, the Etherpath serial server is often used to provide remote serial port access for a computer connected through the TCP/IP network. There are several different methods to use software to complete this connection. We'll discuss the most common approaches and give some examples of code and program packages that are freely available or can be purchased at reasonable cost. The major categories (in order by ease of implementation) are...

  1. Manual telnet access to the Etherpath
  2. Scripted telnet access to the Etherpath using standard communications software
  3. Port redirector software
  4. Custom-written application software

Manual telnet

The easiest way to access the remote serial port is to simply telnet to the Etherpath from a workstation. Once the telnet session is established, all keystrokes are passed through to the Etherpath serial port and any data incoming on that port is passed to the screen of the workstation computer. This is the method most often used for casual access to remote management ports on equipment such as PBX machines, routers, datacom equipment, seldom-used host computers, and other devices that require plain terminal access. For MSWindows users, Windows is installed with a program, telnet.exe, that can be used; or commonly used terminal emulation programs are available such as Procomm, Hyperterm Pro, etc. All unix machines are supplied with a telnet program.

Scripted Telnet

Using the same telnet programs, a script (or batch file) is written to automate the process. This script file may be used to connect to the remote device, cause some control commands to be sent, or read status and log it to a disk file. The Windows programs we have the most experience with are Procomm's ASPECT scripting language, and WRQ's Reflection series scripts. On Unix machines, shell scripts are used with bash or other shells, or more capable scripting languages are used such as perl.

Port Redirector SoftwareWhen PC or Unix application software must access the remote device through an Etherpath connection, and the software can not be modified for TCP/IP communications, the most straight-forward method is to use port redirection software. A port redirector program tricks the computer into thinking that the remote port is actually a local COM: port. This software would be run on the computer workstation, then the application software reads and writes to the COM: port normally... none the wiser. This approach is commonly used with proprietary software that the customer either can't change because of technical or economic factors.

DCB tested a number of port redirector packages, and recommends only a couple. The program of choice for Microsoft Windows (all versions) is Serial/IP by Tactical Software (Download a 30 day trial copy here). This program creates a remote COM: port on the Windows PC that is accessable just like your local physical ports (up to 255 remote ports are available). This excellent package runs on all varieties of Microsoft Windows. After trying it, you can purchase a license for Serial/IP from DCBI f instead, you wish to use DDE connections directly into a spreadsheet or equivalent, TCPWedge, sold by TAL Technologies ( http://www.taltech.com ) is also a quality product, but it doesn't create clean, virtual COM: ports. It's about $200 to $400. They also have a demo version available for download.

TTYD, produced by Joe Croft at www.linuxlots.com, is our favorite port redirector program for most versions of Unix (including Linux, AIX, SCO, BSD). This GNU'd software is available for free download from the DCB site (here), or you can email support@dcbnet.com and get a copy by return email. This outstanding program is provided with C source code.

Custom Software

For specific applications, it makes sense to write a custom program to communicate with the Etherpath. A number of DCB's OEM customers choose this method. For example, if you are using the Etherpath so your alarm system can communicate with remote alarm panels or door release units, the program running on the host computer can be programmed to communicate directly with the Etherpath using TCP/IP network programming.

An example of this approach is available from DCB here. This sample system, written in Visual Basic, retrieves ASCII data from an Etherpath and plots it in a MSWindows screen window. The source of the sample data is another PC, running an included program, that sends the ASCII numbers out its serial port for input to the remote Etherpath.

Another example of this type programming is the "middleware" program example written by Hildeco Oy, Ltd in Finland. Their Visual Basic program allows multiple computers to "control" a single Etherpath and illustrates combining UDP communications to the control computer with TCP/IP communications to the Etherpath. They have graciously made this example of the application available here.

A program example, written in C, is listed in the Etherpath manual under Appendix B. It can be downloaded from here. This is a simple example of network programming in MSWindows. Although DCB has technical support available, customers who implement a custom software solution should have in-house expertise in network programming. By examining these sample programs, most skilled network programmers can produce code that will communicate effectively with the Etherpath.

If programming expertise isn't available, using port redirector software is usually the best approach. The cost and risk is low when implementing this type of solution. Using two Etherpath units in "nailed up" mode to provide a virtual RS-232 cable across the ethernet is even easier since this method requires no software changes at all.

For answers to other implementation questions, send email to info@dcbnet.com or call 800-432-2638. The Etherpath is a quick and easy to install solution. Using it can put your device or product on the Ethernet quickly and economically.
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