SYN/ACK Sequence Numbering

[cessna152]

Lets say I send a SYN with sequeunce number 100. I will recieve an ACK back with sequence number 101. Why is it incremented by 1? Why not just acknowledge the SYN with the same number? I've been trying to figure out a practical reason for this decision but cannot figure out one.

 

[TuxDave]

If you're at Rutgers, you must be taking that telecommunication class where you had to draw a whole bunch of ACK, SYN graphs. I remember those times.

Anyways, I probably need a name of the scheme to fully understand what's going on.

 

[cessna152]

Its just normal tcp/ip protocol. I have two computers. I send a SYN with sequence number 100 to computer two. It recieves the SYN and sends back an ACK with acknowledgement numbr 101. Evidently, there is some reason for this. If the ACK sent back 100 you might encounter some ambiguity; but, I can't figure out what that might be. I've been reading the RFCs on TCP/IP and they all just say add 1 to the sequence number.

 

[TuxDave]

I read the papers and the incrementation of the ACK is more of a signal saying 'what number are they expecting to recieve next'. Then you could do an easy comparison to verify that what you were about to send is equal to what they're expecting. I'm not quite sure how things would be different if the ACK was not incremented on the recieving side but instead on the sending side.

 

[cessna152]

Lol, thats my same thought. Who cares if I increment the number on the recieving side.