OSI model-Session Layer,Presentation Layer,Application Layer

Previous

5)The Session Layer
This layer allows users on different machines to establish sessions between them.
Session offer various services including dialog control,token management and synchronization.

6)The Presentation Layer
This layer is concerned with the syntax and semantics of the information transmitted. The presentation layer manages these abstract data structures and allows higher level data structures (eg.banking records) to be defined and exchanged.

7)Application Layer
This layer contains a variety of protocols that are commonly needed by users.One widely used application protocol is HTTP,which is the basis for the World Wide Web.


Next coming up TCP/IP Model..

OSI model-Network Layer,Transport Layer

Previous

Network Layer
This layer controls the operation of the subnet,how packets are routed from source to destination.
If too many packets are present, such congestion is controlled by network layer.
n/w layer allows heterogeneous n/ws to be interconnected.

Transport Layer
The basic function of the transport layer is to accept data from above,split it up into smaller units if need be,pass these to n/w layer and ensure that pieces all arrive correctly at the other end.
The transport layer is a true end-to-end layer,air the way from source to destination.
The difference between layer1 through 3,which are chained and layers4 through 7,which are end-to-end.

To be continued..

OSI model

The OSI model has 7 layers:

The Physical Layer
Physical layer is concerned with transmitting raw bits over a communication channel. The design issues here largely deal with mechanical,electrical & timing interfaces and physical transmission medium.

2.The Data Link Layer
This layer transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer.In the data link layer a fast transmitter from drowning a slow receiver in data.Frequently, this flow regulation and error handling are integrated. In the data link layer, in broadcast n/w how to control access to the shared channel. A special sublayer of the data link layer, medium Access control sublayer, deals with this problem.

Next

Reference Models

2 important n/w architectures:
The OSI reference model
& TCP/IP reference model

Although the protocols associated with the OSI model are rarely used any more,the model itself is general and still valid,and the features at each layer are still very important.
The TCP/IP model, the model itself is not of much use but the protocol are widely used.

OSI Model
OSI model is based on ISO as a first step toward international standardization of the protocols used in various layers.It deals with connecting open system-systems that are open for communication with other systems. The OSI model has 7 layers.

To be continued..