Thank you Priscilla. Now thing are quite clear. >From now on I have to look out for authors' mistakes.
John Tafasi ""Priscilla Oppenheimer"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > At 09:44 PM 10/31/01, John Tafasi wrote: > >Here is an excerpt of what Mike Crane, author of the Cisco CID Exam > >Certification > >Guide from Cisco Press, is saying in his own words in this book, page 538: > > > >"Another adjustment is to increase the TCP window size to allow more > >outstanding requests. > > What he means is that one can increase the TCP window size to allow more > outstanding packets that haven't been ACKed. ACKs are overhead. The fewer, > the better. > > >This command can also minimize packet fragmentation > >fragmentation, because larger packets means fewer smaller ones" > > That's where he goes astray..... > > > >To me this make sense, because when you decrease the TCP window size you > >will need more IP packets to carry the TCP Traffic. Here the packet > >fragmentation occurs due to the TCP window size limit and not due to the IP > >MTU size limit > > Typical values of the TCP window size are 8,192 bytes and 24,000 bytes, > etc. They are much larger than a single packet size. It would be extremely > bizarre for the window size to be smaller than a single typical IP datagram > size (~1500 bytes). On the other hand, it's not a problem that the window > size is much larger than an IP datagram and it doesn't affect fragmentation. > > The window size is used for flow control. Each side specifies in every > packet how many bytes it is currently able to receive before the other side > should stop and wait for an ACK. As I mentioned, this is usually a large > number, which means the partner sends a few packets without waiting for an > ACK for each one. Each side can have a different window size. PCs usually > have a window size of about 8,192 bytes. I have seen big servers advertise > a window size of 24,000 bytes. > > During the three-way handshake, each side also specifies the maximum > segment (packet) size it is able to receive. Unlike the window size, which > is advertised in every packet, the segment size is added as a TCP option to > the TCP header in a SYN packet. The two sides do not need to agree, but > they usually do. A typical size is 1460 bytes. Add the 20-byte TCP header > and the 20-byte IP header, and you have a typical Ethernet packet. That's a > good thing because otherwise fragmentation would be necessary. > > As an example, if a client says that its segment size is 1460 bytes and its > window size is 8192 bytes, the server on the other end of the connection > will send 5 1460-byte segments and then wait for an ACK. (Well, there's > also the little matter of delayed ACKs and slow start, but ignore those for > now.) > > I wish I had more time to explain it, but any good book on TCP (Comer, > Stevens) explains it correctly. You should also take a look at a TCP > session with a protocol analyzer and it will make sense. > > Unfortunately, the book you are reading does not seem to characterize TCP > correctly. > > Priscilla > > > >What you think guys > > > > > >-- > >watch your phone call records on the web at: > >http://www.freedomstar.com/sh1885969 > > > > > >| > >""Circusnuts"" wrote in message > >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > John- I believe you've let this term confuse you. What you are seeing > >with > > > TCP windowing is how may packets you send before requiring an > > > acknowledgement. This is better know as the sliding window principle, > > > because consistent connections allow the window to open more freely (i.e. > > > larger periods without an ack). When a network hiccup occurs, the window > > > shuts and eases back open when the connection resumes. > > > > > > > >http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ip.htm#xtocid22363 1 > > > 9 > > > > > > All the best !!! > > > Phil > > > > > > ----- Original Message ----- > > > From: "John Tafasi" > > > To: > > > Sent: Wednesday, October 31, 2001 7:25 PM > > > Subject: TCP Window size [7:24875] > > > > > > > > > > Hi Group, > > > > > > > > I have a little but difficut question regarding TCP window size. How > can > > > the > > > > tcp window size configured on a host affect ip packet fragmentation? > >What > > > > will happen if configure a host with a tcp window size that larger than > > > the > > > > ip mtu size? What is the command to configure tcp window size? > > > > > > > > Thanks > > > > > > > > John Tafasi > > > > -- > > > > watch your phone call records on the web at: > > > > http://www.freedomstar.com/sh1885969 > ________________________ > > Priscilla Oppenheimer > http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=25035&t=24875 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
