Manual VIPA CPU 21x Chapter 4 Deployment of the CPU 21x-2BT10 with TCP/IP
HB103E - Rev. 05/45 4-3
ISO/OSI reference model
The ISO/OSI reference model is based on a proposal that was developed
by the International Standards Organization (ISO). This represents the first
step towards an international standard for the different protocols. It is
referred to as the ISO-OSI layer model. OSI is the abbreviation for Open
System Interconnection, the communication between open systems. The
ISO/OSI reference model does not represent a network architecture as it
does not define the services and protocols used by the different layers. The
model simply specifies the tasks that the different layers must perform.
All current communication systems are based on the ISO/OSI reference
model which is defined by the ISO 7498 standard. The reference model
structures communication systems into 7 layers that cover different
communication tasks. In this manner the complexity of the communication
between different systems is divided amongst different layers to simplify
the task.
The following layers have been defined:
Layer Function
Layer 7 Application Layer
Layer 6 Presentation Layer
Layer 5 Session Layer
Layer 4 Transport Layer
Layer 3 Network Layer
Layer 2 Data Link Layer
Layer 1 Physical Layer
Depending on the complexity and the requirements of the communication
mechanisms a communication system may use a subset of these layers.
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