Page 134 - Computer_Science_F5

Open Systems Interconnection Model
The Open Systems Interconnection (OSI) model is a network model that defines
the protocols for network communications. The OSI model was developed by the
International Organisation for Standardisation (ISO). It was developed to allow Chapter Three: Advanced Computer Networks
systems with different platforms to communicate with each other. The platform
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could mean hardware, software, or operating system. The model divides similar
computer communication protocols into seven layers, each layer providing a
specific function to make communication between application processes on various
systems easier. Each layer has specific duties to perform and must cooperate with
the layers above and below it. Figure 3.1 illustrates the seven layers of the OSI
model (top to bottom).

SENDING RECEIVING
SYSTEM SYSTEM
OSI Model Application protocol OSI Model
Application layer 7 Application layer 7
APDU APDU
Presentation layer 6 Presentation protocol Presentation layer 6
PPDU PPDU
Session layer 5 Session protocol Session layer 5
SSDU SSDU
Transport layer 4 Transport protocol Transport layer 4
TPDU Network host-router protocol TPDU
Network layer 3 Network layer 3
PACKET Datalink host-router protocol PACKET
Datalink layer 2 Datalink layer 2
FRAME Physical host-router protocol FRAME
Physical layer 1 Physical layer 1
BIT BIT
PHYSICAL MEDIUM FOR INTERCONNECTION

Figure 3.1: Seven layers of the OSI model

Advantages of the OSI model
(a) Conceptual framework: The OSI model provides a clear and standardised
framework for understanding network communication. It breaks down complex
network processes into seven distinct layers, making it easier to visualise and
troubleshoot network issues.

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Student’s Book Form Five

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