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23 Οκτ 2013 (πριν από 4 χρόνια και 17 μέρες)

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Data Communication

Lecture#4

Abdullah Tayyab


abdullah.tayyab@gmail.com

Presentation Layer


The

Presentation Layer

is Layer 6 of the
seven
-
layer

OSI model

of

computer networking
.



It responds to service requests from the
application layer and issues service request to
the

session layer
.



Receives message from application layer,
formats it, and passes it to the session layer.


Functions of Presentation Layer

Here are some of the specific types of data
handling issues that the presentation layer
handles



Data Format or Translation



Data Security



Data Compression

Syntax



The presentation layer is concerned with the
syntax and semantics of the information
transmitted.




The presentation layer sometimes called the
syntax layer in the (OSI)


is basically used to
address and resolve data communication across
the 7 layers

Syntax Cont..


The presentation layer of the OSI model at the
receiving computer is also responsible for the
conversion of “the external format” with which
data is received from the sending computer to
one accepted by the other layers in the host
computer

Data Security


Another function of the presentation layer is
found in the encryption or protection of data
offered to transmissions/sessions within the
layers


This can be achieved by cryptography.




Cryptography

is a data security science
achieved by hiding information/data in transit.

Data Compression



The goal of data compression is to represent an
information source (e.g. a data file, a speech
signal, an image, or a video signal) as accurately
as possible using the fewest number of bits.

Presention

Layer in TCP/IP model


In TCP/IP, this function is provided
by the Application Layer.


e.g.



External Data Representation Standard (XDR)





Multipurpose Internet Mail Extensions

(MIME)


Session Layer



The fifth layer in the OSI Reference Model is
the

session layer
.



To allow devices to establish and manage

session



Establishes, maintains, and synchronized the
interaction among communicating systems.



occurs.


Cont..


Synchronization



allows a process to add checkpoints, or
synchronization points, to a stream of data.



Responsible for enforcing the rules of dialog
(e.g., Does a connection permit half
-
duplex or
full
-
duplex communication?), synchronizing the
flow of data, and reestablishing a connection in
the event a failure

How Session layer works

Session Layer in TCP/IP model


In
TCP/
IP
, its
characteristics

are provided by the
TCP protocol.


(Transport Layer