Mats Folke wrote:
> 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
>>
>
>
>
>
Dear Mats,
I understood that TCP is a byte-oriented protocol. So, theoretically a
TCP will set the segment size of its own depending upon many factors as
path MTU, etc.
But consider /only one application layer small 'packet'* */being
sent, say of size 200 bytes. (Let's consider this to be small enough to
be accomodated within a single TCP segment.)
Q.>*Now in such a case what will happen in theory?* I know the
answer for 'What will happen in ns2 simulation?". It is as follows: In
ns2, I observed that for this single packet too, TCP sends a single
packet of size 1040 bytes (Rock-Solid-Fixed!!, by the default setting
'Agent/TCP packetSize_ 1000' as you rightly told).
I studied as you asked by changing 'Agent/TCP set pacektSize_
<someOtherSize>'. It works, but it will work *on per flow basis,* while
I need it to work on "/*per packet (segment) basis*/". In short I want
to simulate /*more realistic scenario* in which the segmentSize_ varies
(may be, following some random distribution) continuously. /
* Is it possible in current ns2?* *If not*, (as it is not a perfect
realization of the real network), *what is the way out?*
Regards,
Mayur
