About the three-time handshake when the TCP connection was established, why not 2 or 4 times 5 times

First, the process of "three handshake" in the process of TPC connection establishment is briefly described:

First: client sends connection request like server side

Second time: After the server receives the request, it sends a response and connection request to the client

Third time: After the client receives a request to the server to send a reply

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A total of 3 messages were sent, so the process is also known as the "three handshake"

and 3 of these handshakes are the minimum number of messages that need to be sent during the connection process.

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In this view:

1:

Once a handshake is sent only once by the client, it is certainly not possible to establish a reliable TCP connection

2:

Two handshake: The server does not know if it can send the message, and whether the client on the opposite side can receive it. That is, if the connection is established in the two-time handshake, it is likely that the connection is one-way from the client to the server, that is, the client has been sending messages and the server has been receiving messages.

In addition, the two-time handshake establishes the connection, the server side if sends the message to the client, cannot guarantee to send normally, also cannot guarantee the client to receive normally. So two handshakes can cause both cases: (c means client, s means server side)

1, the process of establishing a connection, C sends a request to s, but for some reason, S did not receive the request, so C sent a request.

S responds to C and makes a request. This time the connection is established, the communication begins, and the connection is terminated. At this point, the first

s did not receive the request suddenly reached the S-end, so s response to this request, due to the assumption of "two times handshake", this time

S thinks that he and C have established a connection, but C does not consider itself and s to establish a connection, which causes the failed request to reestablish the wrong connection

2. If the server is issued and the client does not receive the message, the server repeats the message until it gets a response, wasting a lot of resources

3:

4, 5, 6, 7 handshake: Since the 3-time handshake has ensured a reliable connection, there is no need for multiple handshakes

About the three-time handshake when the TCP connection was established, why not 2 or 4 times 5 times