Siemens Simatic S7-400

The individual layers are as follows:
1. Physical layer
– Physical conditions for communication, e.g. transmission medium, baud rate
2. Data-link layer
– Security procedure for the transmission
– Access modes
3. Network layer
– Network connections
– Speci󹪝es the addresses for communication between two partners.
4. Transport layer
– Error-recognition procedure
– Debugging
– Handshaking
5. Session layer
– Establishing communication
– Communication control
– Terminating communication
6. Presentation layer
– Conversion of the standard form of data representation of the communication system
into a device-speci󹪝c form (data interpretation rules)
7. Application layer
– De󹪝ning the communication task and the functions it requires
Processing the Protocols
The sending communication partner runs through the protocols from the highest layer (no. 7 -
application layer) to the lowest (no. 1 - physical layer), while the receiving partner processes the
protocols in the reverse order, i.e. starting with layer 1.
Not all protocols have to take all 7 layers into account. If the sending and receiving partners both
use the same protocol, layer 6 can be omitted.
2.3 Transmission integrity
Introduction
Transmission integrity plays an important role in the transmission of data and in selection of the
transmission procedure. Generally speaking, the more layers of the reference model are applied,
the greater the transmission integrity.
Basic Principles of Serial Data Transmission
2.3 Transmission integrity
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 21