Basic Operating Modes of Serial to Ethernet Device Servers

Serial to Ethernet also known as S2E devices are increasingly popular in a world where everything is networked. We have found that users who want to utilize S2E either want to network their old legacy devices onto the network or increase communication distance to overcome serial limitations.

But in order to utilize an S2E device, the correct operating mode must be selected. This is dependent on what the user is trying to do and how the end serial device was originally setup.

Driver Mode

The Driver Mode is design for device control applications. To make it simple, the most popular serial application is a host PC connecting to a serial device via the serial port and cable. In most cases, the software is only able to communicate through the serial port. To minimize the configuration, change the existing software, a driver or software will be installed on the PC. The driver/software will create a virtual com port for the existing software. The driver supports both Windows and Linux systems.

1. RealCom (Virtual Com). A proprietary driver/software offered by the manufacturer will be installed on the host PC. The driver creates a serial port (which maps the IP and TCP port of the serial device server) and establishes a transparent connection between the host and the serial device. A static IP address must be assigned on the device server.

2. The RFC-2217 is like the virtual com mode. It allows the users to use third party drivers which supports RFC-2217 to create the virtual com port on the host PC. This operating mode is ideal if there are multiple brand names of serial device servers installed on the network. Third party virtual com software is required.

3. Reverse Real Com: Similar as the virtual com mode, the driver/software will create the virtual com port on the host PC. The major difference is that the device server obtains the dynamic IP address from the DHCP server. With Reverse Real Com, the device server actively initiates a connection to the remote host PC whose IP address is listed as the destination IP on the settings of the device server.

Socket Mode

The serial to Ethernet device server is an IP-based network device. If the software on the host PC supports the TCP/IP protocol, the software can access the serial device directly via the TCP socket. This eliminates the dependence of drivers for the operating systems. The flow control signals can not be transmitted in the Socket Mode.

1. TCP Server: The device server configured with a unique IP address and TCP port number combination. As a “TCP Server”, the device server passively waits to be connected by the host computer. After the connection is established with the serial device, then the data starts to transmit. If needed, The Server can supports up to 8 simultaneous connections. Multiple hosts can collect data from the same serial device at the same time.

2. TCP Client: In the TCP Client mode, the device server establishes a TCP connection with a pre-assigned host computer when serial data arrives. Once the connection is established, data can be transmitted in both directions.

3. UDP: Unlike the TCP socket the receiver need to “acknowledge” the receipt of TCP packets (which is slower on the network), the UDP is faster and more efficient. In this UDP mode, the data can be unicasted or multicasted from the serial device to one or more host computers. The serial device can also receive data from one or multiple host computers. This operating mode is ideal for the RS-485 multi drop.

4. Pair Connection. If neither the host PC nor the device has the Ethernet capability and must use serial cable or connection, the pair connection (two device servers) can be used to remove the distance limitations imposed by the RS-232/422/485. One device server will connect its serial port to the host PC, and the other device server will connect its serial port to the serial device. Then these will connect to each other via Ethernet cable on the same LAN. Pair Connection Mode transparently transfers both data and flow control signals (excludes DCD) between the two devices.

Reverse Telnet

Reverse Telnet is commonly used for device management in telecommunication control rooms. Since the control commands such as CR/LF can not be transmitted by the TCP Server mode, the Reverse Telnet is the best solution for this type of application.

Here are the device servers with the above mentioned functions.

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