Specifications

1 - 6
1.3 Communication Protocol
The MELSEC-Q Ethernet module described here supports two communication
protocols, TCP/IP and UDP/IP.
1.3.1 Communication model
"OSI reference model" is a famous communication mechanism model defined by ISO
(International Organization for Standardization).
This model classifies the functions required for communication into 7 layers.
Layer
Functions Image
Protocol example
7 Application layer
"What the users wants to do"
• Agreement on contents of actual services
• What the users can see
• Available services themselves
Protocol for each application
Remote login TELNET protocol
File transfer
FTP protocol
HTTP
TELNET
FTP
SMTP
6 Presentation layer
"Definition and conversion of data format"
• Definition of data representation system
• Coding/decoding and compression/decompression
of data
• Text code, data format
Data
format
A
Network
common format
Data
format
B
A
bsorption of differences in data representation
MIME
HTML
XML
5 Session layer
"Communication connection establishment"
• Connection establishment/disconnection
• Authentication of connection
• Synchronization for transmitting data
Management of communication connection
RPC
4 Transport layer
"Delivering to the target correctly"
• Securing reliable data transfer between the
source and destination.
• Error correction (arrival sequence correction,
retransmission request)
• Flow control of communication
ACK
Securing of reliability
TCP
UDP
3 Network layer
"Communication procedure with the target not
adjoining”
• Definition of path control (routing)
• Definition of communication path decision
• Establishment of virtual connection using
address
Selection of paths
IP
2 Data link layer
"Dat
a delivery to the next"
• Communication procedure between adjacent
devices.
• Format definition of transmission and reception
data
• Data error detection between devices and
correction method definition
Conversion of frame and bit
Data transfer between adjacent devices
0101
sequence
Ethernet
PPP
1 Physical layer
"Physical
connection"
• Conditions for electrical connection at the
lowest level
• ON/OFF definition of data signals
• Connector shape and pin layout for each signal
0101 0101
Ethernet
ISDN
Telephone line
The bigger numbers correspond to the higher (more logical) layers and the smaller
numbers to the lower (more physical) layers.
IP corresponds to the network layer, and both TCP and UDP to the transport layer.
Ethernet corresponds to the data link layer and the physical layer.