Technical data

118 • ETHERNET
Network Communication
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
5.3 Network Communication
Fieldbus communication between master application and WAGO ETHERNET
controller 750-841 can take place using either the MODBUS protocol or
Ethernet/IP.
The protocol layer model helps to explain the classification and
interrelationships between the communication and application protocols.
Afterwards, the individual protocols are explained in detail.
5.3.1 Protocol layer model
Ethernet:
The Ethernet hardware forms the basis for the physical exchange of data. The
exchanged data signals and the bus access procedure CSMA/CD are defined in
a standard.
(1)
Ethernet
(physical interface, CSMA/CD)
IP:
Above the Ethernet hardware is positioned the Internet Protocol (IP). This
bundles the data to be transmitted in packets along with sender and receiver
address and passes these packets down to the Ethernet layer for physical
transmission. At the receiver end, IP accepts the packets from the Ethernet
layer and unpacks them.
(2)
IP
(1)
Ethernet
(physical interface, CSMA/CD)
TCP, UDP:
a) TCP: (Transmission Control Protocol)
The TCP protocol, which is positioned above the IP layer, monitors
the transport of the data packets, sorts their sequence and sends
repeat requests for missing packets. TCP is a connection-oriented
transport protocol.
The TCP and IP protocol layers are also jointly described as the
TCP/IP protocol stack or TCP/IP stack.
b) UDP: (User Datagram Protocol)
The UDP layer is also a transport protocol like TCP, and is arranged
above the IP layer. In contrast to the TCP protocol, UDP is not
connection oriented. That means there are no monitoring
mechanisms for data exchange between sender and receiver.
The advantage of this protocol is in the efficiency of the transmitted
data and the resultant increase in processing speed.
Many programs use both protocols. Important status information is
sent via the reliable TCP connection, while the main stream of data
is sent via UDP.