Siemens SIMATIC CP 340 User Manual page 29

ISO 7-Layer Reference Model
The reference model defines the external behavior of the communication partners. Each
protocol layer, except for the lowest one, is embedded in the next one down.
The individual layers are as follows:
1. Physical layer
2. Data-link layer
3. Network layer
4. Transport layer
5. Session layer
6. Presentation layer
7. Application layer
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.
PtP coupling and configuration of CP 340
Manual, 04/2011, A5E00369892-03
– Physical conditions for communication, e.g. transmission medium, baud rate
– Security procedure for the transmission
– Access modes
– Network connections
– Addressing for communication between two partners
– Error-recognition procedure
– Debugging
– Handshaking
– Establishing communication
– Communication control
– Terminating communication
– Conversion of the standard form of data representation of the communication system
into a device-specific form (data interpretation rules)
– Defining the communication task and the functions it requires
Basic Principles of Serial Data Transmission
2.2 Transmission mode in Point-to-Point Communication
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