TCP Listen Connection

Overview

One method of connecting to a device and communicating with it is via a TCP/IP connection. Often Port servers are used closer to the devices in the field to convert the TCP/IP communications to Serial for connectivity over Ethernet networks. A TCP/IP link may extend from the machine running ACM all the way to the field device, or it may cover part of the distance and then get converted to a serial connection using hardware such as a port server, terminal server or radio.

TCP/IP ports use socket connections to communicate with field devices. When using TCP Listen, socket connections are opened when polling is required and closed when it is complete. The connection to the end device is not kept open when polling is not required. This port type is a good selection when a communication link to a remote device must be shared between multiple applications. It is also a good selection when the polling frequency is relatively slow. To handle cases where field devices can originate the communication, the TCP Listen module can be configured to listen for incoming socket connections. When incoming socket connection requests are detected, the module will accept the connection and perform any necessary communication with the field device.

Logical ports are defined within ACM to represent a communication method used to connect to a device. Each logical port (Port) has a name that is used to reference it. Whenever a port is used, all of the settings defined by that port are used for communications. Multiple devices and/or multiple device types in ACM can share a single port for communications. 

The TCP Listen Connection releases connections between poll intervals.

Configuration

Once a port has been added to the ACM server, the port must be configured by editing the created object. Configuration may be accomplished using the default Form view. 

Port Tab

Connection Type

The type of connection to establish with the remote address.

• TCP (default)
• UDP
  • Select UDP Receive Port Default = not selected.  Select to use a specific UDP port instead of allowing Windows to select the port.
  • UDP Receive Port Default = 0. The local port to use for receiving UDP communications.

Max Sessions

The maximum number of allowable concurrent socket connections. Default = 1. If multiple devices come due for a poll the TCP Listen port object will poll up to this many devices at a time. As some devices finish polling, others that are still waiting will be added to the active polling list - up to the number configured as the max session.

Delay Polling On Same Connection

Prevent TCP/IP connection conflicts if more than one device becomes due on the same TCP/IP address and port. This will prevent conflicts with the communication port if it only supports a single connection at a time.

Port Release Delay

The length of time in milliseconds to keep control of the port after communication is done.

Initial Data Timeout

The length of time, in milliseconds, to wait for initial data after an incoming socket connection has been accepted. If no data, or no recognizable data, is received during timeout period, the socket is closed. Default = 5000.

Listen Port 1-8

TCP or UDP port number to  listen on. These ports are used to 'listen' for incoming connection requests from field devices that can initiate communication.  (Select Enable to enable this port)

Enable Dialup Modem

Use a modem when communication through this port.