Wireshark · Wireshark-users: [Wireshark-users] about next sequence number in TCP head

["Bo Xu" <xubo.leo@xxxxxxxxx>]

I have found one strange rule in the TCP head , the next sequence number has already been provided .  

i have checked the RFC793 , but nothing methioned about this rule . 

I  dig it for a while , i have found that next sequence number = sequence number + packet size ( the tcp payload )  in wireshark . 

And i have traced the TCP connection for telnet , smpp , i have found it matches this rule .

Can somebody tell me  which document  or RFC includes this mechanism  ?

Here is one example , 

Host A--> Host B 

Sequence number: 1 (relative sequence number)

Next sequence number: 17 (relative sequence number) 

Acknowledgement number: 1 (relative ack number)

then next packet of

Host  A-> Host B 

Sequence number: 17 (relative sequence number)

Next sequence number: 33 (relative sequence number)

Acknowledgement number: 17 (relative ack number)