(OSI) Model Open System Interconnection

The ISO developed the 'Open Systems Interconnect (OSI) reference model' in 1984.

The OSI model has 7 layers as follows:

                              

APPLICATION  LAYER

  Defines the interface between the communications software and any applications that need        communicate outside the computer on which the application resides.

Eg:  WWW, FTP, Telnet, HTTP, NFS, Browsers, SNMP Etc

PRESENTATION LAYER

presents data to the Application layer & is responsible for data translation & code formatting.

compression ,decompression , encryption, decryption.

Eg:- PICT, JPEG, MIDI, MPEG

SESSION  LAYER 

Defines how to start, control, and end conversations (called sessions).

Eg: SQL, X Windows, Remote Procedure Call (RPC). NFS

TRANSPORT LAYER 

Establish end-to-end connections from one computer to another on the network and provide reliable "transport" of data between devices.

TRANSPORT LAYER SERVICES 

Resource Utilization (multiplexing)Connection Management (establishing)

Flow Control (Buffering / Windowing.

Reliable Transport (positive acknowledgment error checking)

Common protocols that operate at the transport layer include TCP, UDP, SPX, and NetBEUI.

NETWORK LAYER 

This manages devices addressing , tracks the location of the device on  the network,& determines the best way to move data.

Router and layer-3 switch works on this layer.

Eg: IP, IPX, Apple Talk, ICMP, ARP, RARP

DATA LINK LAYER 

provides the physical transmission of the data and handles error notification. The data link layer ensures that messages are delivered to the proper device.

Translates messages from the network layer into bits for physical layer to transmit. It formats the message into data frames.

Data link layer has two sub-layers

Logical Link Control (LLC)

Media Access Control (MAC)

MAC layer defines the physical addressing and logical topology.

LLC identify Network layer protocol and then encapsulation them.

Bridges and Switches.

Eg: Frame Relay FDDI, ATM, IEEE, PPP, HDLC.

PHYSICAL LAYER  

How the physical structure of the network enables transmission of data.

The physical layer sends bits and received bits. Bits come in the value of 1 or 0.

Eg: RJ-45, NIC, Cable, HUB.

Peer-to-Peer Communications