HOW IT ALL STARTED ?

Problems are road to inventions.So following were the problems which lead to invention of computer networks ->

1. US Vs Russia -> Russia won space race and then US decided to do better so they
   setuped team of talented researchers for working on data communication.They setuped links between 4 cities using TCP/IP.

2. There was connection between two documents (hyperlink) so WWW was invented to connect the whole world

3. There was no tools for searching documents so seach engine for invented (YAHOO !)

WHAT IS CLIENT SERVER ARCHITECTURE ?

Let us say you typed google.com and clicked search

after click your computer sends request to google servers and in return of it google sends our computer response which consist of html,css,javascript files.

WHAT IS IP ADDRESS ?

1. home address === ip address

2. your video is not sent directly to your friend it is sent in small packets

3. each computer,servers and other computer setups have IP addresses

4. For google.com your hostel laptops connected to hostel wifi have same IP address (global ip address)

5. But for your hostel wifi your hostels laptops have unique IP addresses (local ip address)

WHAT IS PORT NUMBER ? IP addresses decide where data should go and PORT number decides in which application data should go

there are total 16 ports so 2**16 port addresses means 65k ports

There r reserved ports , partially reserved ports and free ports

100 MBPS mean 100000000 bits/sec not 100000000 bytes/sec

SUBMARINE CABLES

Do you think internet is in cloud ? No it is under ocean lol submarine cables

OSI LAYERS

1.Application Layer 2.Presentation Layer 3.Session Layer 4.Transport Layer 5.Network Layer 6.Datalink Layer 7.Physical Layer

APPLICATION LAYER

contains apps guided by protocols

WHAT ARE COOKIES

If you login into amazon.com & then close the tab & when you open amazon.com again after 30 mins then you will be auto logged in .Cookies are responsible for this.

Cookie is a unique string assigned to client.

HOW EMAILS WORK ?

email work via SMTP & POP protocol

sender sends email to sender's SMTP server then SMTP serve sends this email to recievers SMTP server and then reciever downloads email from reciever's SMPT server

WHAT IS DNS

DNS means Domain Name System

1. You search google.com , inorder to access it you need its IP address

2. search Ip address in computer cache memo.

3. If not found go to ISP

4. If not found go to server named DNS ask for IP it will give you

TRANSPORT LAYER

You will send 'Hi' to ayush by using whatsapp , network layer will take this messge to ayush but when msg reaches to ayush's phone it is transport layer which will see that message goes to whatsapp not telegram or signal application.

It consisit of multiplexing and demultiplexing

It uses checksums to encounter errors

You send msg to your friend then you start your timer if you dont get acknowledgement in specific period then you resend it again

UDP Packet

udp packet contains following things :

1. Source Port number
2. Destination Port number
3. CheckSum
4. Length of Data
5. Data

WHAT IS TCP ?

Transport Layer Protocol

Application layer sends lot of raw data TCP segments this data.

It takes data from transport layer and puts it into network layer & vice versa

TCP IN NETWORK LAYER

Routers are present in network layer

src -> youtube.com/watch?v=IPvYjXCsTg8