What is Application Layer|| Presentation Layer ||Session Layer||Transport Layer

What is Application Layer|| Presentation Layer ||Session Layer||Transport Layer



What is Application Layer?

Function of application layer

Problem with application layer

What is presentation layer?

Function of presentation layer

Problem with presentation layer

What is session layer?

Function of session layer.

Problem with session layer

What is transport layer?

Function of transport layer.

Problem with transport layer.



What is Application Layer|| Presentation Layer ||Session Layer||Transport Layer

Application Layer :

OSI Model have to most layer known as application layer.It manipulate the data in various ways.This layer enables users or software to get access to the network.This layer provide some services such as e-mail,transferring files,directory services, network resources etc.
Application Layer contains many protocols such as HTTP(Hyper Text Transfer Protocol),FTP (File Transfer Protocol),TFTP (Trivial File Transfer Protocol),SMTP (Simple Mail Transfer Protocol),TELNET,DNS (Domain Name System)etc.

Functions of Application Layer

  • Mail Services
  • Network Virtual Terminal
  • Directory Services
  • FTAM (File Transfer,Access and Management)

Problem with Application Layer

  • Pattern Language for Application level communication protocols problem.
  • Service Design Patterns problems
  • Patterns of enterprise application architecture problems.
  • Pattern oriented software architecture problems.


The Presentation Layer

The next layer is presentation layer.The primary goal of presentation layer is to take care of the syntax and semantics.This is done when there is exchange of data between two communicating systems.This layer send data in such a way that the receiver will understand and can use the data.

Functions of Presentation Layer

  • Translation of data
  • Encryption of data
  • Compression of data


Problems with Presentation Layer

  • Very difficult to manage and maintain the information of Syntax and Semantics.
  • Encoding of data such as String, double, date, etc.
  • This layer transform the data and ready data for the next layer (application layer).
  • It play a role of translator between communicating systems.


Session Layer:

After physical layer next is Session Layer.This layer allows users on different machines to establish active communication sessions.Session layer have to maintain,establish and synchronize the interaction between sender and receiver.Streams of bit are manage here.The end of the messages should place on end.This layer also avoid to loss data.

Functions of Session Layer

Dialog Control:
Session layer allows two systems for communication in half-duplex/full-duplex.
Token Management:
Session layer prevents two devices to perform the operation on same time.
Session layer allows a process to add checkpoints.This point is consider as synchronization points.

Problem with Session Layer:

  • This layer allow machines to establish sessions between them.
  • It provide enhance services to the user.
  • It is difficult to manage dialog control.
  • It is difficult to provide services such as Token management and Synchronization for every message.


Transport Layer

Transport layer accept data from session layer.This layer divide data into smaller units.These units further pass to the Network layer.It give acknowledge that all units arrive correctly at the other end.This layer determines what type of service should provide to the Session layer.
Mostly we use point to point channel in transport connection to send and receive messages.The Transport layer is the only way to send message from the source to the destination.

Functions of Transport Layer:

  • These are functions that are perform in the transport layer.
  • Service Point Addressing
  • Segmentation and Reassembling
  • Connection Control
  • Flow Control
  • Error Control


Problem with Transport Layer:

  • It accept data from Session layer,then divides it into segments.
  • It must ensure correct delivery of message with efficiency.
  • It isolate upper layers from below layers.
  • Flow control and Error control.
  • This layer decides about data transmission.This can be on single path and parallel path.
  • Multiplexing, Segmenting or Splitting are done by transport layer.


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