At 07:37 AM 5/27/02, Pierre-Alex Guanel wrote: >I understand that when a host is sending an acknowledgement, it indicates to >the target the NEXT segment number that it expects to receive.
It's kind of a picky thing, but it's not accurate to say that the ACK indicates the number of the next segment the host expects to receive. TCP sequences bytes, not segments. The ACK number indicates the next byte the hosts expects to receive. Of course, every segment has many bytes in it. The Window field specifies how many bytes the host is ready to receive. >When host A sends acknowledgement number X to host B, why does B sets its >sequence number to X+1? It doesn't. It sets the sequence number to the ACK number. Where are you getting this info? It's not right. The first thing I check when reading a description of TCP is whether they know that bytes (not segments) are numbered. If they don't, I don't read the rest. Also, be careful if they don't go beyond explaining the 3-way handshake. Since the SYN, SYN ACK, and ACK packets don't actually have any data bytes in them, the sequence number behaves a little differently. They only go up by one, making it appear that segments are sequenced, rather than bytes. client sends: SYN initial seq number = 50 server sends: SYN initial seq number = 99, ACK = 51 client sends: ACK 100 client sends: bytes 51-100 server sends: ACK 101 client sends: bytes 101-150 ETC. Actual size of packets depends on Max Segment Size (and how much data the upper layer has to send). Actual number of packets sent before stopping and waiting for ACK depends on the window size. Check RFC 793, Stevens, Comer, many books other than "pass the Cisco test quick" books. ;-) Priscilla >I would expect B to set its sequence number to X, >since X is already the next segment number ... > >thanks > >Pierre-Alex ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=45151&t=45131 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
