Communication
8.4 Ethernet
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
417
Open user communication
8.4.7.1
Open User Communication (OUC) provides a mechanism for your program to transmit and
receive messages over an Ethernet network. You can select the Ethernet protocol used as
the transport mechanism: UDP, TCP, or ISO-on-TCP
Note
The CPU models CPU CR20s, CPU CR30s, CPU CR40s, and CPU CR60s have no
Ethernet port and do not s
upport any functions related to the use of Ethernet
UDP (User Datagram Protocol)
User Datagram Protocol (UDP) uses a simple connectionless transmission model with a
minimum of protocol overhead. There is no handshake mechanism in UDP protocol so the
protocol is only as reliable as the underlying network. There is no guarantee of delivery,
ordering, or duplicate message protection. UDP does provide checksums for data integrity
and generally uses different port numbers to address different functions.
TCP (Transmission Control Protocol)
Transmission Control Protocol (TCP) is a core internet protocol. TCP provides a reliable,
ordered, and error-checked delivery of messages between applications running on hosts
communicating over an Ethernet network. TCP guarantees that all bytes received are
identical with the bytes sent, and in the original order. TCP protocol creates a connection
between an active device (the device that initiates the connection) and a passive device (the
device that accepts the connection). Once a connection is established, either device can
initiate a transfer of data.
TCP protocol is a "streaming" protocol. This means that there is no end sign included in a
message. All the messages that are received are considered to be part of a "stream" of data.
For example, the client device sends three messages of 20 bytes each to a server. The
server sees only a "stream" of 60 bytes received (assuming the server executes a receive
operation after the three messages are received.)
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