Chapter 2: The OSI Model

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23 Οκτ 2013 (πριν από 3 χρόνια και 5 μήνες)

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University of the Western Cape

Chapter 2: The OSI Model

Aleksandar Radovanovic

University of the Western Cape

Network Communication


The most basic level of computer information consists of binary digits, or bits (0s
(zeros) and 1s).


In order for computers to send information through a network, all communications
on a network originate at a source and then travel to a destination.


Computers that send one or two bits of information, however, would not be very
useful. Other groupings, bytes, kilobytes, megabytes, and gigabytes are therefore
necessary.


In order for data packets to travel from a source to a destination on a network, it is
important that all the devices on the network speak the same language or protocol.

University of the Western Cape

OSI Reference Model

The OSI reference model, released in 1984 by International
Organization for Standardization (ISO) is the primary
model for network communications.




It breaks network communication into smaller parts to
make it easier to understand.



It standardizes network components to allow multiple
-
vendor development and support.



It allows different types of network hardware and
software to communicate with each other.



It prevents changes in one layer from affecting the other
layers, so that they can develop more quickly.


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The 7 Layers of the OSI Model

University of the Western Cape

Encapsulation

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Peer
-
to
-
Peer Communications


Communication between the same OSI reference model layer in two
different network devices


During this process, the protocol of each layer exchanges information,
called protocol data units (PDUs), between peer layers.

University of the Western Cape

The TCP/IP Reference Model

Application layer handles high level protocols,
issues of representation, encoding, and dialog
control.


The transport layer deals with the quality of
service issues of reliability, flow control, and
error correction.

The purpose of the internet layer is to
send packets and have them arrive at the
destination.

Network Access Layer includes the LAN
and WAN technology details.

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Similarities



Both have layers


Both have application layers, though they include very different services


Both have comparable transport and network layers


Packet
-
switched (not circuit
-
switched) technology is assumed


Differences



TCP/IP combines the presentation and session layer issues into its application layer


TCP/IP combines the OSI data link and physical layers into one layer


TCP/IP appears simpler because it has fewer layers, however this is a misconception.


The OSI reference model, with its less complex and multiple layers, is simpler to develop


TCP/IP protocols are the standards around which the Internet developed




typically networks are not built on the OSI protocol.

Comparison of the OSI and the TCP/IP model

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Labs



2.3.4

(homework)
In this lab, you will learn to relate the seven layers
of the OSI model to the four layers of the TCP/IP model as well as name
the primary TCP/IP protocols and utilities that operate at each layer.


2.3.5

(homework)

In this lab, you will identify the characteristics of
each layer as well as the terminology and physical devices that operate at
each layer.



Interactive Labs:



2.3.5

(homework)

Test your knowledge of the functions of the OSI
Model layers.