TCP question...

rjbarlow

Hi all,
I was sure that I comprised the dynamic of the TCP protocol, but it is arising to me a doubt that I don't succed to answer...
Let's take that hostB is sending segments to hostA starting from a SEQ. number of 41000.
HostA receives correctly the first segment and send an ACK. number of 42300 to hostB, because it expects to receive next 1300 bytes of payload.... But at this point arise the problem: how do hostA to know exactly the payload that hostB will send next to him?

hostA <

---

SEQ. number 41000

---

hostB

hostA

---

ACK. number 42300

---

> hostB

I thought at the method of the windowing, but in the Window field it's present just the value of bytes that the sender can send, not the value that the sender must send. I thought also to the value of Maximum Segment Size (MSS) in the Options field, but I'm not sure if it's used for that specific purpose.

dtlokee

the ACK will indicate the number of bytes successfully received, not the number that is expected in the next segment. so if the sequence number is 41500 then the ack would be 41501 to indicate it received up to that point successfully.