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(1) Role of IP

lP is a network layer protocol which is processed by all devices connected to an IP network.

The most important role of the TCP/IP (UDP/IP) network is "data transfer to a device or PLC at the target address".

This role is achieved by IP (Internet Protocol).

Data (packets) are delivered with the information called "IP header" (tag) attached.

(2) Restrictions on IP

Although IP transfers data to a target PLC, there are some restrictions.

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) No guarantee to reach the destination I 3 11 I 2 11 1111 —► QP network '

(b) No guarantee to reach in the order of sending

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(c) As the transfer size at one time is limited, a packet may be divided into several pieces at transmission. (¹1)

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(d) No guarantee for no data damage

To put it shortly, IP bends every effort to transfer data (packets) to the target device or PLC, however, it does not guarantee delivery of packets (Best effort).

Notę that, there is no need to consider these restrictions when using TCP over IP. When using UDP as a higher layer, care should be taken sińce the above restrictions apply except the data damage detection.

1

1 The size of one message (1 packet) that can be transmitted by the Ethernet module is upto 1500 bytes (including the IP header).

Data exceeding 1500 bytes are divided in either case of the TCP/IP or UDP/IP communication. The divided data are reassembled into one data on the receiving side and handed to the application program.