How TCP 3 way Handshake works ?

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 TCP Protocol

         TCP  known as Transmission Control Protocol is a  transport layer host-to-host protocol that provides a reliable communication over IP networks between two endpoints.

TCP - A Reliable Protocol

         TCP provides recovery of segments that get lost , damaged , duplicated over the end to end communication. The most used protocols like HTTP and SMTP uses TCP methodology.

TCP Flags



·         SYN – The SYN, or Synchronisation flag, is used as a first step in establishing a 3-way handshake between two hosts.

·         ACK – The ACK flag, which stands for “Acknowledgment”, is used to acknowledge the successful receipt of a packet. 

·         FIN – The FIN flag, which stands for “Finished”, means there is no more data from the sender. 

·         URG – The URG flag is used to notify the receiver to process the urgent packets before processing all other packets.   

·         PSH – The PSH flag, which stands for “Push”, is somewhat similar to the URG flag and tells the receiver to process these packets as they are received instead of buffering them.

·         RST – The RST flag, which stands for “Reset”, gets sent from the receiver to the sender when a packet is sent to a particular host that was not expecting it. 

·         CWR – The CWR flag, which stands for Congestion Window Reduced, is used by the sending host to indicate it received a packet with the ECE flag set. See RFC 3168 for more details. 

·         NS (experimental) – The NS flag, which stands for Nonce Sum, is still an experimental flag used to help protect against accidental malicious concealment of packets from the sender. See RFC 3540 for more details.





TCP 3 ways Handshake

  The TCP three-way handshake method used SYN-SYN-ACK method while the communication between the hosts.


TCP 3-Way Handshake Diagram

Below is a (very) simplified diagram of the TCP 3-way handshake process. Have a look at the diagram on the right as you examine the list of events on the left.
EVENTDIAGRAM
Host A sends a TCP SYNchronize packet to Host B
Host B receives A's SYN
Host B sends a SYNchronize-ACKnowledgement
Host A receives B's SYN-ACK
Host A sends ACKnowledge
Host B receives ACK. 
TCP socket connection is ESTABLISHED.
tcp three-way handshake,syn,syn-ack,ack
TCP Three Way Handshake
(SYN,SYN-ACK,ACK)







 

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