OSI Reference Model

OSI Reference Model:


For a networking student and beginners first and foremost important thing to understand how LAN and WAN works they first have to study complete model of a basic general network, OSI model is complete interactive way to learn different stages of network and how data flows across entire network when and where different protocols come into play, to learn all basics about network you first have to study OSI Model.


In this post we will discuss about OSI model and its diffrent stages very briefly.


OSI stands for open system interconnection model. In 1984, the Open Systems Interconnection (OSI) reference model was approved as an international standard for communications architecture. Term “open” denotes the ability to connect any two systems which conform to the reference model and related standards.


Definition:

OSI model is a conceptual model for distributed applications and networking protocols.This model defines the framework networking used for the implementation of the protocols present in Seven layers.The seven layers of OSI model is given in the above image . Now i discussed all these layers in detail.


Layer 1, Layer 2 and Layer 3 concerned with the Network Administrator related .

Layer 4, Layer 5, Layer 6 and Layer 7 concerned with the System Administrator related.





Seven Layers of OSI Reference Model


1. Application Layer:

This layer is close to the user and provides networks services to the user's application.FTP, SMTP, HTTP etr. (protocols are used in this layer). Word Processing , Spreadsheet Programs are example of these applications e.g. Hello Message sent.


Application are of two types:

1. Desktop Application

2. Network Application

Desktop Application

“Provides interface between user and computer”
Example:- VLC Player, Microsoft Word etc.

Network Application

“Provides interface between user and Internet”
Example:-Yahoo message in internet, CV.doc desktop to internet(Any word file) etc.


2.Presentation Layer:

Presentation Layer serves as a translator between the application and the network and Simply data are in computer understandable form Manages data encryption ,decryption and compression e.g. Hello message sent Examples :- JPEG, MPEG, ASCII, HTML etc.

3.Session Layer:

This layer defines how to start, control and end conversations (called sessions) between applications Virtual session create between host and server . e.g. hotmail page through session then server available or not Examples :- SQL, ASP(AppleTalk Session Protocol),

DHCP(Dynamic Host Configuration Protocol) etc.


4. Transport layer:

This layer regulates information flow to guarantee end-to-end connectivity between host applications reliably and accurately. Major properties of this layer are Data Segmentation, Flow Control and Error Control , Data rate, Speed , Bandwidth and Cock rate measured ,Rate of transmission is determined in this layer . TCP , UDP protocol implement in this layer ,TCP connection Oriented Protocol & UDP connection Less Protocol.


5. Network

Network layer provides logical addressing and best path , Network layer is just like a post office , In post office sorting and distribution of letters. Similarly, in network layer data are sorting own the basis of IP addresses. IP protocol also implement in this layer . There are two protocol categories exist in it :

 1.Routing Protocols 2. Routed Protocols



Routing Protocols

“Routing Protocols are those protocols which provides the best path for destination end”


Routed Protocols

“Routed Protocols are those protocols which deliver the data on the destination place ”

OR


“Data Career”


Routing can be categorized:- 1. Static Routing 2. Dynamic Routing


Static Routing

No Protocols implement in it and It itself do administrative work


Dynamic Routing

Protocols implement such as OSPF, RIP etc. Protocols works in it.



Important points:-


IP(IPV4) address are 32 bits(4 bytes)


e.g. 192.168.1.1

IP are routed protocols/ Data careers and IP address is an identifier(Network device identify).

IPV6 address are 128 bits  Routers device used in this layer






6. Data Link Layer:

In data link layers frames of data are transmitted from the same network segments between computers.eg. Point to point Protocol , Ethernet and Frame relay etc .Data Link Layer are divided in to two sub layers MAC (Media Access Control ) Layer(Medium established) . LLC (Logical Link Control ) Layer(Link provide to physical layer.






7. Physical Layer:


Physical layer is Implementation of standards without software(Only H/W used) e.g. Cables , Hub, connectors(RJ-45) are used It Control data Transmission mode and bit synchronization and it is bottom most layer but layer 1 considered the most important and basic layer in OSI model, its also called media layer or medium layer. If you don't have medium in you network then all other processing is just waste of time. In this layer we understand behaviour of medium , its bandwidth, noise etc