2.2 Transmission Procedure with a Point-to-Point Connection
Introduction
When data are transmitted, all communication partners must adhere to a xed set of rules for
handling and implementing data trac. The ISO has dened a 7-layer model, which is
recognized as the basis for a worldwide standardization of transmission protocols for computer-
to-computer communication.
ISO 7-Layer Reference Model for Data Transmission
All communication partners must adhere to a xed set of rules for handling and implementing
data trac. Such rules are called protocols.
A protocol denes the following:
• Operating mode
Half-duplex or full-duplex operation
• Initiative
Which communication partners can initiate data transmission and under what conditions
• Control characters
Which control characters are to be used for data transmission
• Character frame
Which character frame is to be used for data transmission
• Data backup
The data backup procedure to be used
• Character delay time
The time period within which an incoming character must be received
• Transmission speed
The baud rate in bits/s
Procedure
This is the specic process according to which the data is transmitted.
ISO 7-Layer Reference Model
The reference model denes the external behavior of the communication partners. Each
protocol layer, except for the lowest one, is embedded in the next one down.
Basic Principles of Serial Data Transmission
2.2 Transmission Procedure with a Point-to-Point Connection
Point-to-point connection CP 440 Installation and Parameter Assignment
20 Equipment Manual, 03/2022, A5E00057742-AE
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