Hi! It is a fundamental property of TCP to set the packet (segment) size of its own. This is set with respect to path MTU, and various buffers. Thus, the size of the incoming FTP packets will not impact the outgoing segment size, since TCP is a byte-oriented protocol.
However, ns-2 is not a perfect realization of the real world. There is a parameter Agent/TCP set packetSize_ 1000 # packet size used by sender (bytes); at http://www.isi.edu/nsnam/ns/doc/node396.html. Perhaps that may help you? Many wishes, Mats Folke Mayur wrote: > Tatiana Polishchuk wrote: >> Did you try to change the header size? Pls refer to the chapter >> 12.1.2 >> of the ns2 tutorial. >> Tatiana >> >> On Thu, Sep 25, 2008 at 9:03 AM, Mayur <[EMAIL PROTECTED] >> <mailto:[EMAIL PROTECTED]>> wrote: >> >> >> Dear all, >> >> I am using simple FTP over TCP. In ns, from the application >> layer (ftp) Though I send small packets, (eg. 100 bytes >> using '$ftp_($i) send 100' ), TCP's packet size remains fixed >> equal to 1000. What is the reason? How to change it. >> >> I tried to study the tcp.cc's send and sendmsg() function, but >> could not understand it well. >> >> Your cooperation is appreciated. >> >> regards, >> Mayur >> >> > Thank you Tatiana, for your quick response! > > I went through 12.1.2 of the ns Manual as you suggested. > > I know that each layer will add a header to the SDU (Service Data > Unit) received from its upper layer. And so, there is no point in > reducing the header size. My point is different. Consider following > explanation. > > at Application layer the data from FTP is > ------------------------------- > | FTP data | > ------------------------------- > Now when this is handed over to the TCP layer, it will add its header > to it. And it will become following to be handed over to IP layer and > so on... > ---------------------------------------------------------- | > TCP Header | FTP Data | > ---------------------------------------------------------- > That's fine. So, the total size, at the TCP layer should be = > FTPDataSize + TCPHeaderSize. > > *Now, the problem I face is: *The TCP packet size is always remaining > same (1040 bytes), irrespective of the FTPDataSize, which I expect to > vary with it. eg. for FTPData of 200 bytes it should become > (200+TCPHeaderSize) bytes. I think theoretically I am correct, and > something I miss to set in the ns2. The expert users' suggestions are > awaited. > > I hope my question is now clear.... > > > regards, > Mayur -- Mats Folke, M.Sc., Tech.lic Research Engineer Ericsson AB Office: +46 8 7571385 Ericsson Research Fax: +46 920 99621 P.O. Box 920 Mobile: +46 76 1271385 SE-971 28 Luleå
