In the
‘open communication’
the communication takes place via the user program by
means of handling blocks. These blocks are also part of the Siemens SIMATIC Manager.
You will find these in the
‘Standard Library’
at
‘Communication Blocks’
.
n
Connection-oriented protocols:
Connection-oriented protocols establish a (logical) connection to the communication
partner before data transmission is started. And if necessary they terminate the con-
nection after the data transfer was finished. Connection-oriented protocols are used
for data transmission when reliable, guaranteed delivery is of particular importance. In
general, many logical connections can exist on one physical line. The following con-
nection-oriented protocols are supported with FBs for open communication via Indus-
trial Ethernet:
–
TCP native accord. to RFC 793:
During data transmission, no information about the length or about the start and
end of a message is transmitted. However, the receiver has no means of
detecting where one message ends in the data stream and the next one begins.
The transfer is stream-oriented. For this reason, it is recommended that the data
length of the FBs is identical for the sending and receiving station. If the number
of received data does not fit to the preset length you either will get not the whole
data, or you will get data of the following job.
–
ISO on TCP accord. to RFC 1006:
During data transmission, information on the length and the end of the message
is also transmitted. If you have specified the length of the data to be received
greater than the length of the data to be sent, the receive block will copy the
received data completely into the receive range.
n
Connection-less protocol:
There is thus no establishment and termination of a connection with a remote partner.
Connection-less protocols transmit data with no acknowledge and with no reliable
guaranteed delivery to the remote partner.
–
UDP accord. to RFC 768:
In this case, when calling the sending block you have to specify the address
parameters of the receiver (IP address and port number). During data transmis-
sion, information on the length and the end of the message is also transmitted. In
order to be able to use the sending and receiving blocks first you have to con-
figure the local communications access point at both sides. With each new call of
the sending block, you re-reference the remote partner by specifying its IP
address and its port number.
Open communication
System 300S
+
Deployment Ethernet communication - productive
Basics - Protocols
HB140 | CPU | 315-4PN23 | en | 18-02
105
