what is iso/osi referrence model

There are seven layers

1).Application layer
2).presentation layer
3).session layer
4).Transport layer
5).Network layer
6).Datalink layer
7).physical layer

Physical Layer


Specification of voltage levels, cables, connectors, timing of bots, electrical access and maintenance of circuit (i.e. corresponds to the basic hardware).

Data Link Layer

Transforms basic physical services to enable the transmission of units of data called frames. Frames carry data between two points on the same type of physical network, and may be relayed if the network is extended. They normally contain low level addressing information and some error checking. This layer may be involved in arbitrating access to the physical network. The Data Link layer detects, and possibly corrects errors in the physical layer

Network

Controls routing of data by providing an address domain, and in consequence the routing of messages. This addressing is separate from the hardware which implements the network connections. i.e. specifies how addresses are assigned and how packets are forwarded from one end of the network to another.

Transport

Provides an interface for the upper layers to communications facilities. The presence of this layer obscures the underlying network hardware and topology from the applications. A very complex set of protocols are required for this layer!

Session

The protocols for this layer specify how to establish a communication session with a remote System (e.g., How to login to a remote timesharing computer). Specifications for security details such as authentication using passwords are described in this layer.

Presentation

Layer 6 protocols specify how to represent data. Such protocols are needed because different brands of computer use different internal representation for integer and characters. Thus layer 6 protocols are needed to translate from the representation on one computer to the representation on another.

Application Layer

This is where the application using the network resides. Common network applications include remote login, file transfer, e-mail, and web page browsing.