Basic Principles of Serial Data Transmission
2-6
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02
2.2
Transmission Procedure with a Point-to-Point Connection
When data is transmitted, all communication partners involved must follow fixed
rules for handling and implementing the data traffic. The ISO has defined a 7-layer
model, which is recognized as the basis for a worldwide standardization of
transmission protocols for computer-to-computer communication.
2.2.1
ISO 7-Layer Reference Model for Data Transmission
Protocol
All communication partners involved in data transmission must follow fixed rules for
handling and implementing the data traffic. Such rules are called protocols.
A protocol defines the following points:
•
Operating mode
Half-duplex or full-duplex mode
•
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 transmission rate in bps
Procedure
This is the specific process according to which the data is transmitted.