OSI model

what is networking model ?

what is networking model ?

Networking models categorize and provide a structure for networking protocols and standards

what is protocols ?

A set of rules defining how network devices and software should work . Including how they should work together .

what if there were no standard networking models and protocols ?

These dells would be able to communicate with each other , and these iMacs Would be able to communicate with each other , but because the dells and imacs would speak a different language then each other , with a different set of rules about how to communicate , The dells wouldn’t be able to communicate with the imacs.

OSI (open systems interconnection model )

What is the OSI ？ (1 Open , means tat it is an open standard , not a proprietary model developed and used by an individual company . (2 a conceptual model that categorizes and standardizes the different functions in a network . (3 created by the ‘international organization for standardization (ISO)’ (4 network functions are divided into 7 layers (5 these layer work together to make the network work layer application (1 this layer is closet to the end user . (2 the application layer interacts with software applications , for example your web browser ,firefox. http and https are layer 7 protocols ,these protocol tat interact with the application ,like http or https (3 function of layer 7 include : identifying communication partners layer presentation (translates data to the appropriate format.) 1）data in the application is in an ‘application format ‘ , a format that applications understand It needs to be translated to a different format to be sent over the network 2）The presentation layer’s job is to translate between application and network formats 3） one example of a function of the presentation layer is encryption of data as it is sent ,so that only the intended recipient can read it , and of course decryption as it received layer session (1 The sessions layer controls dialogues between communicating hosts . (2 establishes ,manages , and terminates connections between the local application (web browser) and the remote application (youtube) layer transport (begin to add the header) (1 segments and reassembles data for communications between end hosts

(2 breaks large pieces of data into smaller segments which can be more easily sent over the network and ate less likely to cause transmission problems if errors occur .

it data wasn’t segmented and you were trying to watch a video , if an error occurred that prevented the video form reaching your computer , you wouldn’t be able to watch the video at all However, if the data is segmented into many small units , and only one fails to reach the destination , that’s not a big problem . The video might skip for a second , but then will continue on just fine

(3 provide host-to-host communication also know as end-to-end communication layer network ( 1 provides connectivity between end hosts on different networks

(2 provides logical addressing (ip addresses )

(3 provides path selection between source and destination .

(4 router operate at layer 3 layer data link (1 Provide node-to-node connectivity and data transfer(pc to switch , switch to router (2 defines how data is formatted for transmission over a physical medium (copper UTP ) (3 detects and corrects physical layer errors. (4 switch operate ;at layer 2 physical layer ( 1 defines physical characteristics of the medium used to transfer data between devices (2 digital bits are converted into electrical or radio (for wireless )

Date is prepared by the application layer (include 7 6 5 ) A layer 4 header is added to the data to make a segment . A layer 3 header is added to the segment to make a packet . A layer 2 header and layer 2 trailer are added to the packet . it is called frame

Synchronizing communication

Here we have two OSI model stacks , representing two computers that will communicate with each other . The software application , maybe a web browser , interacts with layer 7 , the application layer ,and wants to send some data to the system on the right.

This data is processed though the OSI stack , each layer adding something to the original data. (this processed is called encapsulation ,because the original data is encapsulated inside this additional information which is added on )

By the time it reaches the physical layer , it is electrical signals on a wire , and is sent to the neighboring system .

Then , the neighboring system performs the opposite process , the additions of each layer are stripped off until the data reaches the application layer of the neighboring system (this process is called ‘de-encapsulation’, as the additional information is removed as the data is processed up the stack .)