OSI Reference Model
Layers 5– 7: Session, Presentation, and Application Layers
Let’s look at the upper layers of the OSI seven layer
model now. Those layers are the transport, session, presentation, and application
layers.
Session Layer
- Network File System (NFS)
- Structured Query Language (SQL)
- Remote-Procedure Call (RPC)
- X Window System
- AppleTalk Session Protocol (ASP)
- DEC Session Control Protocol (SCP)
The session layer establishes, manages, and terminates sessions among applications.
This layer is primarily concerned with coordinating applications as they interact
on different hosts. Some popular session layer protocols are listed here, Network
File Systems (NFS), Structured Query Language or SQL, X Window Systems; even AppleTalk
Session Protocol is part of the session layer.
Presentation Layer
The presentation layer is primarily concerned with the format
of the data. Data and text can be formatted as ASCII files, as EBCDIC files or
can even be Encrypted. Sound may become a Midi file. Video files can be formatted
as MPEG video files or QuickTime files. Graphics and visual images can be formatted
as PICT, TIFF, JPEG, or even GIF files. So that is really what happens at the
presentation layer.
Application Layer
The application layer is the highest level of the seven layer
model. Computer applications that you use on your desktop everyday, applications
like word processing, presentation graphics, spreadsheets files, and database
management, all sit above the application layer. Network applications and internetwork
applications allow you, as the user, to move computer application files through
the network and through the internetwork.
Examples:-
COMPUTER APPLICATIONS
- Word Processor
- Presentation Graphics
- Spreadsheet
- Database
- Design/Manufacturing
- Project Planning
- Others
NETWORK APPLICATIONS
- Electronic Mail
- File Transfer
- Remote Access
- Client-Server Process
- Information Location
- Network Management
- Others
INTERNETWORK APPLICATIONS
- Electronic Data Interchange
- World Wide Web
- E-Mail Gateways
- Special-Interest Bulletin Boards
- Financial Transaction Services
- Internet Navigation Utilities
- Conferencing (Voice, Video, Data)
- Others
Related Topics
- SUMMARY -
- OSI reference model describes building blocks of
functions for program-to-program communications between
similar or dissimilar hosts
- Layers 4–7 (host layers) provide accurate data delivery between
computers
- Layers 1–3 (media layers) control physical delivery of data
over the network
The OSI reference model describes what must transpire for program
to program communications to occur between even dissimilar computer systems. Each
layer is responsible to provide information and pointers to the next higher layer
in the OSI Reference Model.
The Application Layer (which is the highest layer in the OSI model) makes available
network services to actual software application programs.
The presentation layer is responsible for formatting and converting data and ensuring
that the data is presentable for one application through the network to another
application.
The session layer is responsible for coordinating communication interactions between
applications. The reliable transport layer is responsible for segmenting and multiplexing
information, keeping straight all the various applications you might be using
on your desktop, the synchronization of the connection, flow control, error recovery
as well as reliability through the process of windowing. The network layer is
responsible for addressing and path determination.
The link layer provides reliable transit of data across a physical link. And finally
the physical layer is concerned with binary transmission.
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