You send a message
You wait
Still no reply
Left on read you think ?
But thats not the case someone is between you and her that wants acknowledgment first
No its not her bff
Its TCP...
So... In this blog we will discuss :
What are data packet and what it contains ?
What is TCP and why is needed ?
Problems TCP is designed to solved
What is the TCP 3-way Handshake ?
Step by step working of SYN , SYN-ACK and ACK
How data trasfer works in TCP ?
How a TCP connection is closed ?
Data Packets
Think of you , sending a long message to your friend on whatsapp .
So behind the scene the internet breaks your message into small peices and send it seperately and it will ressemble them at the recieivers side
👉 A data packet is small unit of data in which your message is broken before treaveling over a network
If you dont know about network i recommend you to read this blog first 👇
Now lets see how a data packet look like
It consist of three components :
- Header :- It is the travel guide of a packet 🙎♂️ . It contains :
Sender IP address ( from where )
Reciever IP address ( to where )
Packet number ( order )
Protocol info ( TCP / UDP )
Payload :- It is the actual data what you want to send .
Trailer :- It is the method of identifying the end of packet . Also , some form of error checking to ensure packet is arrives at the recievers end .
Now message is sent to your friend . But there are some rules that these data packets follow or we can say some protocols
TCP : Transmission Control Protocol
Rohan wants to send a invitation letter to his friend vikas
Before sending anyting he calls his friend
Rohan :- Are you home tommorow ?
Vikas :- Yes , why ?
Rohan :- Sending you a letter
Connection established
If vikas says no i am not free then rohan dont send utill vikas confirms
👉 TCP is a protocol ( a set of rule ) that :
Allows devices to communicate over a network .
Establishes a connection between sender and receiver before data transmission begins .
It ensure that data reaches correctly at its destination in right order even if the network is slow .
It is slow as compare to UDP (Uer datagram protocol) but ensure that there is no data packet loss between communication .
It is slow but that doesn't mean its not usefully both are usefull at its own usecase
What does TCP do if the packet is missing or out of order ?
If missing/lost
TCP send the missing packets back to the sender and ask it to send the packet again
If Out of order
TCP wait , reorder them , before delivering the data
Problems TCP is designed to solved
TCP solves reliabilty and guaranteed deliver of data packets to the reciever.
Problem solved right ? But how the TCP is so sure that the data packet reaches at the reciever correctly without any missing or out of order 🤔
TCP : 3-way Handshake
SYN :- Synchronize, A request sends by sender to receiver to ask if communication can begin .
SYN-ACK :- A response confirming the request was received and the receiver is ready .
ACK :- Acknowledgment , its is the confirmation send by sender that TCP is connected .
TCP three-way handshake is nothing its just each packet has to be acknowleged as delivered by recipient .
First , the sender sends a packet . It like knocking on your friend door.
Your know the address but you are not sure if your friend is at home . It is SYNSecond , Your friend reply with SYN-ACK . "I am here , come in" . It means your friend receives the packet .
Finally , the sender send ACK . "Okay , connection established . Now we can talk " . It means the connection is build between sender and receiver and no data packet can loss now
TCP connection successfull . Now how data transfer works in this
How does data transfer in real life
TCP tries to connect or established the network between sender and receiver via three - way handshake .
If the connection is successfull your data (image , message etc) is break down into chunks of packet called data packet .
Now , these data packets are send sequentially with their number .
Receiver sends an acknowledgment that they receive these data packets .
Lost packets resent by the sender , out of order packets are rearranged
After all the data is delivered . TCP closed its connection .
Once all the data is deliverd TCP also define how a connnection is safely terminated .
TCP Termination : 4-way handshake
Closing a TCP connection requires a four-way handshake to ensure that both side finish transmitting data safely .
FIN (Finish) :- First , The sender who wants to close their connection send a FIN segment to the receiver . It is ready to close connection and waiting for the receiver .
ACK (Acknowledge) :- Now this FIN receives by the receiver and acknowledge with ACK .
FIN from receiver :- The receiver then send its own FIN to sender that it is also ready to close the connection .
ACK :- The sender reponds with an ACK , completing the termination .
This ensures that all remaining data is transmitted before the connection is fully close
Thanks for reading ! if enjoyed this blog , you can read more on this 👇
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