Computer Networks Slides Full Syllabus

1. CS-324 Computer Networks

2. Presentation Layer
Unit -06-02

3. UNIT-06-02
• Session Layer, Design issues, remote procedure call.
• Presentation Layer, Design issues, Data compression
techniques, cryptography.
• Application Layer - File Transfer, Access and Management,
Electronic mail, Virtual Terminals, Other applications,
Example Networks - Internet and Public Networks.

4. Presentation Layer
• Presentation layer format and encrypts data to be sent across
the network.
• Takes care that the data is sent in such a way that the receiver
will understand the information (data) and will be able to use the
data efficiently and effectively.
• Manages the abstract data structures and allows high-level data
structures (example- banking records), which are to be defined
or exchanged.

5. Presentation Layer
• This layer basically deals with the presentation part of the data.
• Presentation layer, carries out the data compression (number of bits
reduction while transmission), which in return improves the data
throughput.
• This layer also deals with the issues of string representation.
• The presentation layer is also responsible for integrating all the
formats into a standardized format for efficient and effective
communication.
• This layer encodes the message from the user-dependent format to
the common format and vice-versa for communication between
dissimilar systems.

6. • This layer deals with the syntax and semantics of the
messages.
• This layer also ensures that the messages which are to be
presented to the upper as well as the lower layer should be
standardized as well as in an accurate format too.
• Presentation layer is also responsible for translation, formatting,
and delivery of information for processing or display.
• This layer also performs serialization (process of translating a
data structure or an object into a format that can be stored or
transmitted easily).

7. Presentation Layer
• Presentation layer deals primarily with data representation
• If one host supports Extended Binary-coded Decimal Interchange
Code (EBCDIC) for character sets and another supports ASCII, the
presentation layer converts data according to each hosts’ needs
• Other functionalities include
• data compression,
• data encryption, and
• manipulating XML objects

8. File Formats: Graphic Images
• Layer 6 standards also determine how graphic images are presented.
• Three of these standards are as follows:
• PICT - a picture format used to transfer QuickDraw graphics between
programs on the MAC operating system
• TIFF (Tagged Image File Format) - a format for high-resolution, bit-
mapped images
• JPEG (Joint Photographic Experts Group) - graphic format used most
often to compress still images of complex pictures and photographs

9. File Formats: Sound and movies
• Other Layer 6 standards guide the presentation of sound and movies.
Included in these standards are the following:
• MIDI (Musical Instrument Digital Interface) - for digitized music
• MPEG (Motion Picture Experts Group) - standard for the compression
and coding of motion video for CDs and digital storage
• QuickTime - a standard that handles audio and video for programs on
a MAC operating system

10. File Formats: text
• ASCII and EBCDIC are used to format text.
• ASCII text files contain simple character data, and lack any sophisticated
formatting commands, such as boldface or underline.
• Notepad is an example of an application that uses and creates text files.
• They usually have the extension .txt.
• EBCDIC is very similar to ASCII in that it also does not use any sophisticated
formatting.
• The main difference between the two is that EBCDIC is primarily used on
mainframes and ASCII is used on personal computers

11. File Formats: Graphics
The Internet uses two binary file formats to display images - Graphic
Interchange Format (GIF), and Joint Photographic Experts Group (JPEG).
Any computer with a reader for the GIF and JPEG file formats can read these
file types, regardless of the type of computer.
Readers are software programs designed to display an image of a particular
file type.
Some programs can read multiple image types as well as convert files from
one type to another.
Web browsers have the ability to display graphic files in either of these two
formats without any additional software

12. File formats: Multimedia
• The multimedia file format is another type of binary file, which stores
sounds, music, and video.
• Sound files generally operate in one of two ways.
• They may be completely downloaded, first, and then played, or they may
download while they are playing.
• The latter method is referred to as streaming audio.
• Windows uses the WAV format for sound, and the AVI format for
animation files.
• A few of the more common video formats are MPEG, MPEG2, and
Macintosh QuickTime.

13. File formats: Markup Language
• Another type of file format is markup language.
• This format acts as a set of directions that tell a Web browser how to
display and manage documents.
• Hypertext Markup Language (HTML) is the language of the Internet.
• HTML directions tell a browser whether to display text, or to hyperlink
to another URL.
• HTML is not a programming language, but is a set of directions for
displaying a page

14. Data Encryption
Layer 6 is also responsible for data encryption. Data encryption
protects information during its transmission.
Financial transactions (e.g. credit card information) use encryption to
protect sensitive information as it traverses the Internet.
An encryption key is used to encrypt the data at its source and then to
decrypt the data at its destination

15. Data Compression
• The presentation layer is also responsible for the compression of files.
• Compression works by using algorithms (complex mathematical
formulas) to shrink the size of the files.
• The algorithm searches each file for repeating bit patterns, and then
replaces them with a token.
• A token is a much shorter bit pattern that represents the long pattern.
• A simple analogy might be the name Cathy (the nickname), the token,
to refer to anyone whose full name is Catherine.

16. Presentation Layer Protocols
Presentation Layer, for performing translations or other specified
functions, needs to use certain protocols which are defined below
–
• Apple Filing Protocol (AFP): Apple Filing Protocol is the
proprietary network protocol (communications protocol) that
offers services to macOS or the classic macOS. This is
basically the network file control protocol specifically designed
for Mac-based platforms.

17. Presentation Layer Protocols
• Lightweight Presentation Protocol (LPP): Lightweight
Presentation Protocol is that protocol which is used to provide
ISO presentation services on the top of TCP/IP based protocol
stacks.
• NetWare Core Protocol (NCP): NetWare Core Protocol is the
network protocol which is used to access file, print, directory,
clock synchronization, messaging, remote command execution
and other network service functions.

18. • Network Data Representation (NDR): Network Data
Representation is basically the implementation of the
presentation layer in the OSI model, which provides or defines
various primitive data types, constructed data types and also
several types of data representations.
• External Data Representation (XDR): External Data
Representation (XDR) is the standard for the description and
encoding of data. It is useful for transferring data between
computer architectures and has been used to communicate
data between very diverse machines. Converting from local
representation to XDR is called encoding, whereas converting
XDR into local representation is called decoding.

19. Presentation Layer Protocols
• Secure Socket Layer (SSL): The Secure Socket Layer
protocol provides security to the data that is being transferred
between the web browser and the server. SSL encrypts the link
between a web server and a browser, which ensures that all
data passed between them remains private and free from
attacks.