This is article two in a series of DECserver How Do I articles. In the last article I summarized the different DECserver software versions. This week I will discuss using RFC2217 to send COM port configuration data to a DECserver. It is important to note that RFC2217 in only supported in DNAS V3.3 or greater on the following devices.
- DECserver 90M+
- DECserver 708
- DECserver 716
- DECserver 732
- DECserver 900TM
- DECserver ConX4
RFC2217 is an extension of the Telnet protocol, which is used to access serial devices over the network. The Telnet protocol alone is not sufficient to support sending COM port configuration data to a DECserver. However, the RFC2217 COM Port Control protocol enables applications to set the parameters (baud rate, flow control, etc.) of remote serial ports, detect serial line status changes, as well as receive and transmit data with the use of COM Port Redirector software. RFC2217 allows users to access the serial port on a DECserver as if it were a local serial port, allowing for a wider range of PC application software to be used successfully.
Although there are many COM Port Redirector software products available on the market, the DECservers have been tested by Tactical Software and confirmed to work with their Serial/IP COM Port Redirector product. They offer the following solution overview:
- DECservers are located near field devices and connected to their serial ports
- The DECservers are connected to a TCP/IP network. The Internet is used in the example illustrated.
- The Serial/IP Redirector is installed on each application computer.
- For each serial device in the field, a Serial/IP virtual COM port is created and configured with the IP address of a DECserver and the unique TCP port number on that server that corresponds to the serial device.
Advantages
- Devices can be located any distance from the application server.
- The number of devices is not limited by the number of serial ports on the application server.
- Communication is faster and less expensive than modems.
- Application software is unchanged, using Serial/IP virtual COM ports instead of local hardware COM ports.
If your application or device expects to see serial control signals (DTR, DCD, etc.), then you will need to use a serial server that supports The COM Port Control Protocol (RFC 2217). Many serial-based applications and the devices to which they connect, expect to see hardware control signals just as if they were directly connected to an RS-232* port. When using these applications and devices, it is imperative that you use a serial server that supports the COM Port Control Protocol.
With the combination of the RFC2217 compliant DECserver and COM Port Redirector software from Tactical Software, you’ll be able to access the DECserver’s COM ports with your application.
*DECserver products are RS-423 compliant and RS-232 compatible.