Re: send sizes in stream_tests

todd j. derr (
Fri, 31 Jul 1998 08:43:43 -0400 (EDT)

The send size is at the application layer.

In the case of UDP_STREAM, this does map easily to packet size by adding
the encapsulation - just remember to consider IP fragmentation, which will
happen if your data size is > 1472 bytes in the case of ethernet.

For TCP_STREAM, there is no direct correlation between the send size and
the frame size - the TCP layer treats the data as a stream, boundaries
between calls to write(), etc. are _not_ preserved. The frame size depends
on a number of factors, and in general is not predictable. Your best bet
here is to use 'snoop' or 'tcpdump' or some other traffic analyzer to look
at the frames that are sent.


> About the send sends in XXX_STREAM_TEST's could anyone tell what layer
> of the seven layer model the send size refers to as I need translate
> send size in acutal frame sizes to comply with RFC 1944 to measure
> thurput,
> : e.g a 4kb stream. Is that 4kb being send from the application layer,
> which means by the time it reachs the physical layer the actual size
> send is increased due to encapsulation by the lower levels.
> or is the send size at the physical layer which in the case 4kb
> includes higher level encapsulation (heads and the like).

todd j. derr      fore systems, inc.      (724) 742-7365