What’s the Sequence Number in TCP header?
Sequence Number has an important roll for accurate connection, so I’ll explain about it.
As assumption, the Sequence Number is 32 bit, meaning to take a value between 0 and 4,294,967,295 (32nd power of 2).
In the 3 way handshake
In the 3 way handshake, there are 3 steps.
①SYN
②SYN/ACK
③ACK
In these 3 steps, SWQ and ACK are below.
①SYN⇒SEQ:0, ACK:0
②SYN/ACK⇒SEQ0, ACK:1
③ACK⇒SEQ:1, ACK:1
When server receive the segment
When server receive the segment, server add the value of the byte to the ACK, e.g. if server receive the 100byte segment, server response the segment with ACK101(100+1).
What’s the effect of Sequence Number?
So, what’s the effect of Sequence Number?
For example, if the segment sent by the client is lost during the communication, server can notice it from the difference between the Sequence Number and the byte the server received.
How about in UDP?
So how about in UDP?
In the case of UDP, UDP doesn’t use sequence number, and there isn’t sequence number in UDP header in the first place.
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