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Related Content: CS601 - VU Lectures, Handouts, PPT Slides, Assignments, Quizzes, Papers & Books of Data Communication
Presentation Layer
- This layer is concerned with Syntax and Semantics of info exchange between two systems

Functions of Presentation Layer
- Translation
- The processes (running programs) in two systems are usually exchanging
info in the form of character strings, numbers and so on…..
- The info should be changed to bit streams before being transmitted
- Because different computers use different ENCODING SYSTEMS, presentation layer is responsible for interoperability b/w these different encoding methods
- The presentation layer at the sender changes the info from its sender- dependent format to the common format
- The presentation at the receiver changes info from common to the receiver dependent format
- Encryption
- To carry sensitive info , a system must be able to assure privacy
- Encryption means that sender transforms original info to another form and sends the resulting message out over the network
- Decryption reverses the original process to transform message back to its original form
- Compression
- Data compression reduces the number of bits to be transmitted
- Data compression becomes particularly important in transmission of multimedia such as text, audio and video
Application Layer
- Enables the user either human or software to access the network
- It provides user interface and support for the services such as Electronic mail, Remote File access and Transfer, Shared Database Management and other services
Application Layer Figure

- In the figure, of many application services available, only three services are shown
- X-400 (message Handling Services)
- X-500 (Directory Services)
- File Transfer, Access& Management (FTAM)
- In this example user uses X-400 to send an e-mail message
- No headers or trailers are added at this layer
Application Layer Functions
- Network Virtual Terminal
- NVT is a software version of a physical terminal and allows a user to log on to a remote host
- To do so the application created emulation of terminal at the remote host
- Users computer talks to the software terminal which in turn talks to the host *& vice versa
- Remote host believes it is communication with one of its own terminals and allow you to log on
- File Transfer, Access & Manage.(FTAM)
- This application allows a user to access file on the remote computers to make changes or read data
- The purpose of this access is to Retrieve files from a remote computer and to manage or control files in that remote computer
- Mil Services
- This application provides the basis for email forwarding and storag
- Directory Services
- Provides distributed database sources and access for global info about various objects and services
Summary of Layer Functions

TCP/IP Protocol Suite
- Transmission Control Protocol / Internetworking Protocol
- Developed Prior to OSI Model
- Widely used in the Internet Today
Layers in TCP/IP Protocol Suite
- Physical (physical standards)
- Data Link (N/w Interface)
- Network (Interconnectivity)
- Transport(Transport Functions)
- Application(Session , Pres, app of OSI)
TCP/IP Protocol Suite

Summary
- The OSI Model
- Functions of Layers
- TCP/IP Protocol Suite
Reading Sections
Section 3.2, 3.3 “Data Communications and Networking” 4th Edition by Behrouz A. Forouzan