Communication via Ethernet CPs in S7 stations
1.6 Open communications services (SEND/RECEIVE interface)
Configuring and commissioning S7 CPs for Industrial Ethernet
Configuration Manual, 09/2013, C79000-G8976-C182-13
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ISO transport provides services for the reliable transfer of data on configured connections.
Due to segmentation (packetoriented segmentation - the completeness of the message is
detected) large amounts of data can be transmitted.
Transmission reliability is extremely high due to automatic repetition and additional field
check mechanisms. The communications partner confirms reception of data and the sender
receives a return value on the SEND/RECEIVE interface.
ISO transport is operated only on Industrial Ethernet and is optimized for highperformance
operation at the selfcontained manufacturing level.
The following methods are available for internetwork data transfer:
● ISO-on-TCP connection
ISOonTCP is intended for reliable, internetwork data transfer.
The ISOonTCP service corresponds to the TCP/IP standard (Transmission Control
Protocol/Internet Protocol) with the RFC 1006 extension according to layer 4 of the ISO
reference model (see /18/).
RFC 1006 extends the TCP protocol by allowing the transfer of blocks of data
("messages"). This requires that both partners support RFC 1006.
Transmission reliability is extremely high due to automatic repetition and additional field
check mechanisms. The communications partner confirms reception of data and the
sender receives a return value on the SEND/RECEIVE interface.
● TCP connection
When using the SEND/RECEIVE interface on TCP connections, the Ethernet CP
supports the socket interface (for example, Winsock.dll) to TCP/IP found on almost every
system (PC or other system).
TCP is intended for reliable internetwork data transfer.
The TCP service complies with the TCP/IP standard (Transmission Control
Protocol/Internet Protocol).
● UDP connection
UDP is intended for simple internetwork data transfer without confirmation.
If the connection is suitably configured, broadcast and multicast frames can also be sent
on UDP connections.
To avoid overload due to high broadcast load, the CP does not allow reception of UDP
broadcasts. As an alternative, use the multicast function over a UDP connection. This
allows you to register the CP as a node in a multicast group.
Data transfer is triggered by the user program. The interface to the user program in the
SIMATIC S7 is formed by special SIMATIC S7 program blocks.
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