Omron CS1W-ETN21 operation manual FINS/TCP Method, FINS/TCP Features

FINS/TCP Method Section 6-3

6-3 FINS/TCP Method

6-3-1 Overview

FINS/TCP Features

The FINS/TCP method is a FINS communications method that uses the TCP/ IP protocol. TCP/IP is a connection-type communications protocol. Before a message is sent from one node to another, it is necessary to establish a vir- tual circuit, i.e., a connection. Once a connection has been established, com- munications are quite reliable. The arrival of data that is sent via the connection is confirmed by an acknowledgement (ACK) response, and retries are executed automatically as required.

The FINS/TCP method has been newly added to the CS1W-ETN21 and CJ1W-ETN21 Ethernet Units.When FINS/TCP is used, it must be determined which node is the server and which is the client.

For communications between a personal computer and a PLC, the computer should normally be set as the client and the PLC as the server. For communi- cations between two PLCs, either one can be set as the client and the other as the server.

Node

(Client)

Node

(Server)

Request to establish a connection

Connection established

Acknowledgement

Data transmission 1

Acknowledgement

An acknowledgement is received whenever a connection is established or data is sent, so transmissions are more reliable but somewhat slower.

Compared to the FINS/UDP method, the FINS/TCP method has the following characteristics.

•Data transmission is more reliable, due to factors such as retry process- ing at the TCP/IP layer. The FINS/TCP method is thus better suited to dealing with communications errors in an IP network that spans several layers.

•Remote clients can be restricted by means of settings at the server (i.e., the server can be protected from access by non-specified IP addresses).

•Broadcasting cannot be used.

•TCP/IP has various retry procedures, and this tends to lower its perfor- mance in comparison with UDP/IP.

•There is a limit to the number of connections that can be made (i.e., 16 connections maximum), and any given node can communicate only with up to 16 other nodes at a time.

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