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Unformatted text preview: SI model is found in its expression of how
networking actually functions. Network communications occur over a physical connection. This is true
even if wireless networking devices are employed. Physical devices establish channels through which electronic signals
can pass from one computer to another. Physical device channels are only one type of the seven logical channel
types defined by the OSI model. Each layer of the OSI model communicates via a logical channel with its
peer layer on another computer. This enables protocols based on the OSI model to support a type of
authentication by being able to identify the remote communication entity
as well as authenticate the source of the received data.
Lecture-3 5 Encapsulation/De-encapsulation
OSI layers add a head and trail to
encapsulate the message.
Encapsulation occurs as the data
moves down through the OSI model
layers from Application to Physical.
The inverse action occurring as data
moves up through the OSI model
layers from the Physical to Application
is known as de-encapsulation.
Lecture-3 6 Encapsulation/De-encapsulation
The Application layer creates a
2. The Application layer passes the
message to the Presentation layer.
3. The Presentation layer encapsulates
the message by adding information to
it. Information is added at the
beginning of the message (called a
header) and at the end of the message
(called a footer).
1. Encapsulation/Deencapsulation Process …
cont. Lecture-3 8 Encapsulation/De-encapsulation Process …
cont. At the Physical layer, the message is
converted into electrical impulses
that represent bits and is transmitted
over the physical connection.
6. The receiving computer captures the
bits from the physical connection and
re-creates the message in the
7. The Physical layer strips off its
information and sends the message 9
5. Encapsulation/De-encapsulation Process …
cont. The Data Link layer strips its
information off and sends the
message up to the Network layer.
9. This process of de-encapsulation is
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This note was uploaded on 01/21/2014 for the course IT 205 taught by Professor Kurts during the Winter '08 term at University of Phoenix.
- Winter '08