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LECTURE
Presentation Layer
ith Syntax and Semantics of info exchange between two systems
Functions of Presentation Layer o Translation
sses (running programs) in two systems are usually exchanging info in the form of character strings, numbers and so on…..
SYSTEMS, ifferent
the common format
o Enc
ensitive info , a system must be able to assure privacy Encryption means that sender transforms original info to another form and
o Com
ber of bits to be transmitted
o This layer is concerned w
The proce
The info should be changed to bit streams before being transmitted Because different computers use different ENCODING presentation layer is responsible for interoperability b/w these d encoding methods The presentation layer at the sender changes the info from its sender- dependent format to The presentation at the receiver changes info from common to the receiver dependent format
ryption
To carry s
sends the resulting message out over the network Decryption reverses the original process to transform message back to its original form
pression
Data compression reduces the num
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Data compression becomes particularly important in transmission of
Application Layer
er human or software to access the network ectronic mail,
Application Layer Figure
multimedia such as text, audio and video
o Enables the user eith o It provides user interface and support for the services such as El Remote File access and Transfer, Shared Database Management and other services
o In the figure, of many application services available, only three services are
400 (message Handling Services)
agement (FTAM) o In t ssage
Application Layer Functions
Network Virtual Terminal
o NVT is a software version of a physical terminal and allows a user to log on to
plication created emulation of terminal at the remote host host
elieves it is communication with one of its own terminals and allow you to log on
shown
- X-
- X-500 (Directory Services)
- File Transfer, Access& Man his example user uses X-400 to send an e-mail me o No headers or trailers are added at this layer
a remote host o To do so the ap o Users computer talks to the software terminal which in turn talks to the *& vice versa o Remote host b
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TCP/IP Protocol Suite
Reading Sections
unications and Networking” 4th Edition by Forouzan
Summary
The OSI Model Functions of Layers TCP/IP Protocol Suite
Section 3.2, 3.3 “Data Comm Behrouz A.
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