TCP 3 Way Handshaking

Question

In TCP 3 way handshaking mechanism why the data is not started being transmitting from the 3rd step itself I.e.

1. A-> B / SYN FROM A

2. A<-B / SYN AND ACK FROM B

3. A-> B / ACK FROM A.

Comments

Its a 3 way handshake process. Before data transfer both client and server should go to established state. In the 2nd step server said that "I am ready to start.Are you ready?" and in 3rd step client responded by sending ACk that "Yes.I m ready" :)

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Yes exactly then I think in the third step only the client should trabsmit the data. But don't know the geniun reson behind it.

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I am sorry but I am not getting you at all. What do you mean only client should transmit the data?

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@rahul sharma5 I mean to say that the client (which initialize the connection) wants to send the data to server, then client will send SYN X, in turn Server will send {SYN Y, ACK X+1}, after getting Server's control signal the Client will send {ACK Y+1}. Upto here Every thing is correct, but client can send the data in the third step only but attaching the data in the control packet, but I don't have any solid proof regarding this fact. Do you have any geniun reason about it.

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This is how the protocol is designed.It is a just a way server wants to confirm that client is also ready to start communication.May be after receiving syn+ack client don't want to communicate,so why should server go to established state?

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I think it is because:

1) When client(who initialize the connection) wants to receive some data from the Server then after 3rd step it will wait for data to be come in, it is the case where client is not sending the data first.

2) When client (who initialize the connection) wants to send the data to the Server then it can start transmission just after 2nd stage i.e. in 3rd state by padding the data bits from the header of the TCP packet.

So, in general we don't know the from which direction the data will be sent, that's why it will start transmission after the 3rd step. So, to ensure that after third step the data from any side i.e. from client to server or from server to client. will start to transmit.

Please check it @Bikram Sir, @rahul sharma 5.

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 Shubhanshu

see this https://serverfault.com/questions/369056/tcp-whats-the-purpose-of-the-third-step-of-3-way-handshake

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@Bikram Sir,

I am also saying the same as second answer is saying.

but it seems that first answer is also saying the same thing.

Answer 1

"The third stage of the three-way handshake may carry client-to-server data in the segment payload." - Kurose and Ross

Comments

third stage may also contain data from client ( connection initializer) to server.Then in this case we can transfer the data to server in third stage also.

Answer 2

TCP is connection oriented Protocol , so First you have to sure whether the server you want to send packet is available or not . so, in the first step

Step :1 -  it send randomly generated sequence no. and SYN = 1 (means client interested to synchronized with server ) .

Step: 2 - then server send Randomly generated sequence no. ,  SYN=1(means client interested to synchronized with server ) , ACK=1 

Step 3 : - at last sender send Next sequence number , ACK=1 (client say to server that i got your response so, i am sending Next sequence number ) .

Then , how can you directly started with step 3 ?????????????

Comments

have u heard “piggybacking’’ bcoz thats the answer of your question