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MELSEC-F
OVERVIEW1
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(2) UDP (User Datagram Protocol)
This protocol may not guarantee data credibility or reliability in communication
between a personal computer/work station and PLC that are connected via
network. Thus, even if the data does not reach the target node, it will not be
retransmitted.
• Because it is connectionless, communication efficiency is much improved than
TCP/IP.
• A check sum is used to increase the reliability of the communication data.
When greater reliability must be maintained, a user application or TCP should
be
used for retrying operation.
(3) IP (Internet Protocol)
• Communication data is sent and received in datagram format.
• Communication data can be divided and reassembled.
• Routing option is not supported.
(4) ARP (Address Resolution Protocol)
• This protocol is used to get the Ethernet physical addresses from the IP
addresses.
(5) ICMP (Internet Control Message Protocol)
• This protocol is used to exchange errors which occur on an IP network and
various information related to the network.
• Provides a function to transmit IP error messages.
• See Appendix for information regarding the types of ICMP supported.
(6) DNS (Domain Name System)
• This system translates IP addresses to names that are easy to remember by
the user.
(7) SMTP (Simple Mail Transfer Protocol)
• This protocol transfers mail.
(8) POP3 (Post Office Protocol Ver. 3)
• This protocol transfers mail received by a mail server to a local computer.
(9) Flag bit of TCP/IP (SYN, ACK, PSH, FIN, RST, and URG)
In communication using TCP, these flag bits indicate segments where
connection/disconnection or response confirmation is executed or emergency
data is included.
1) SYN (Synchronized Flag)
When this bit is ON (1), it indicates that the initial sequence number value
is set in the sequence number field.
This bit is used when the connection is newly opened.
2) ACK (Acknowledgment Flag)
When this bit is ON (1), it indicates that ACK (confirmation response
number) field is valid.
It also indicates that this segment includes the information on response
confirmation.
When this bit is OFF (0), it indicates that ACK (confirmation response
number) field is invalid.