THE PRESENTATION LAYER OF THE OSI MODEL
Hi visitor, welcome to the page that TRIES to tell u about the
presentation layer of the
OPEN SYSTEMS INTERCONNECTION (
THE PRESENTATION LAYER
The presentation layer is the sixth layer of the OSI
model. It responds to service requests from the application layer and issues
service request to the session layer.
The presentation layer performs certain functions that are
requested
sufficiently often to finding a general solution for users,
rather
than letting each user solve the problems. In particular, unlike all the lower layers, which are just interested in moving bits reliably from here
to there, the presentation layer is concerned with the syntax and semantics of the information transmitted.
The presentation layer sometimes called the syntax layer
in the OPEN SYSTEMS INTERCONECTION MODEL (OSI) is basically used to address and resolve data
communication across the 7 layers. For example, a sending computer after
receiving data from the application layer will need to convert such data from
the receiving format(eg
ASCII) to a format understood and accepted by other layers of the OSI model
to ensure smooth file transfer.
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 formats include postscript, ASCII,
or BINARY such as EBCDIC (fully Extended
Binary Coded Decimal Interchange Code)
An example of data formating
functions of the presentation layer is the conversion of an EBCDIC-coded data
to an ASCII style.
However, the presentation layer has more
duties other than data/file formatting. This includes data compression and security of transmitted information which is
achieved through encryption.
Encryption can be
achieved with the use of cryptography-this function is however argued at
times as the function of the session/network layer-(follow other web-links
for suggestive reading)
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. Although, there are
other forms of cryptography such as the use of microdots or merging words
with images, today’s computing world is largely concerned with encryption-
the process of scrambling plaintext-e.g. everyday
sentences and messages into ciphertext -a language
understood by the machine or translator at the receiving end which is then
interpreted into plaintext again i.e. decryption. This
function is however debated as one not exclusive to the presentation layer
alone but also other layers of the
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.
www.datacompression.com/index/shtml
A
simple characterization of data compression is that it involves transforming
a string of characters in some representation (such as ASCII) into a new
string (of bits, for example) which contains the same information but whose
length is as small as possible. Data compression has important application in
the areas of data transmission and data storage which
inadvertently
is the main concept behind the OSI layers. Many data processing applications
require storage of large volumes of data, and the number of such applications
is constantly increasing as the use of computers extends to new disciplines.
At the same time, the proliferation of computer communication networks is
resulting in massive transfer of data over communication links. Compressing
data to be stored or transmitted reduces storage and/or communication costs.
When the amount of data to be transmitted is reduced, the effect is that of
increasing the capacity of the communication channel. Similarly, compressing
a file to half of its original size is equivalent to doubling the capacity of
the storage medium. It may then become feasible to store the data at a
higher, thus faster, level of the storage hierarchy and reduce the load on
the input/output channels of the computer system.
So
typically, in the presentation layer, the layout/structure of data in transit
is set, language to be used
in transmission is agreed on, security features are
put in place to guarantee privacy and authentication, and the volume of data to be transmitted
is decided through compression.
SUGGESTIVE
Cisco Networking Simplified by Paula
Del Maggiora and Jim Doherty. Printed in July 2004
MCSE Networking Essentials for
Dummies by Robert Aschermann.
Operating Systems incorporating UNIX
and Windows 4th Edition by Colin Ritchie, published by Continuum
in 2003.
Operating Systems International
Edition Third Edition, by Gary Nutt published in 2004
FOR LINKS TO OTHER RELATED SITES, CLICK
BELOW PLS
www.ics.uci.edu/~dan/pubs/DataCompression.html
www2.rad.com/networks/1994/osi/present.htm
en.wikipedia.org/wiki/Presentation_layer
www.webopedia.com