why not a two way handshake, why a three way handshake

[rookie1010]

Hello,

you guys might have heard this question before, i basically want to know why we cant have a two way handshake, why is a three way handshake necessary.

why does a TCP/IP handshake need to be three-way. why can't it be two-way?

e.g. client A tells server B i want to communicate with you (Sync)
Server B tells Client A ok let's talk (sn/ack)

and then client A and server B can start talking, why then the need for the three way handshake?

 

[spidey07]

It's needed it to syncronize and acknowledge that both sides' sequence numbers are acceptible.

1) Sync, here's my sequence number and MSS

2) Acknowledged, your SEQ is good and I will use this as your SEQ number, here's mine plus my MSS.

3) Acknowledged, I will use your SEQ number for you

Without the sequence numbers you have don't have the reliable delievery of a connection-oriened transport layer. (TCP)

 

[RebateMonger]

Because, if Server B never hears back from Client A, how does Server B know that Client A can "hear" what it's saying?

Different analogy:

--You asked a question here.
--spidey07 and I answered the question.
--We never heard back from you? How do we know if you read our answers? Do we need to email you the answers?

 

[rookie1010]

thanks for the replies

makes sense guys,
one more question, why a three way handshake for security?

 

[Dagne]

Assume the first Sync message from the sender did not reach the reciever. Then, is the management of this problem the same when we consider 2 way handshake and 3 way handshake? thank you.

It's needed it to syncronize and acknowledge that both sides' sequence numbers are acceptible.

1) Sync, here's my sequence number and MSS

2) Acknowledged, your SEQ is good and I will use this as your SEQ number, here's mine plus my MSS.

3) Acknowledged, I will use your SEQ number for you

Without the sequence numbers you have don't have the reliable delievery of a connection-oriened transport layer. (TCP)