Omron CS1W-ETN21 operation manual FINS/UDP Method, Overview, FINS/UDP Features

FINS/UDP MethodSection 6-2

6-2 FINS/UDP Method
6-2-1 Overview
FINS/UDP Features	The FINS/UDP method is a FINS communications method that uses the UDP/
	IP protocol. UDP/IP is a connectionless communications protocol. When a

message is sent from one node to another, the two nodes have an equal rela- tionship and there is no clear connection. If using TCP is like making a tele- phone call, then UDP is more like delivering a memo by hand. Although the UDP protocol is fast, data communications are less reliable than with TCP.

In particular, when sending large amounts of data involving significant routing, the user must program measures, such as retries, into applications in order to improve reliability.

Node

Node

Data transmission 1

Data transmission 2

Data transmission 3

Data is sent in one direction, with no confirmation of whether the data was received. Because there are few procedures involved, data can be sent at high speed but with less reliability than with TCP.

The FINS/UDP method has the following features:

•Because FINS/UDP is a connectionless protocol, there is no limit to the number of corrections.

•FINS/UDP can be used for broadcasting.

•When data is sent via an IP network with multiple layers (such as the Internet), communications reliability drops.

FINS/UDP Frame Format The following diagram shows the structure of a UDP packet used for sending

and receiving data on an Ethernet network.

Ethernet Ver. 2

IP

UDP

FINS frame

FCS

UDP packet

As the diagram shows, a nested structure is used with the FINS/UDP method, i.e., Ethernet Ver. 2, IP frame, UDP frame, and FINS frame. A UDP data sec- tion (FINS frame) that exceeds 1,472 bytes is split into packets for transmis- sion. The split UDP data is then joined automatically at the UDP/IP protocol layer. There is normally no need to pay attention at the application layer to this split, but it may not be possible to send 1,472-byte UDP packets over an IP network with multiple layers. When using the FINS communications service in a system such as this, select the FINS/TCP method.

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