[Beowulf] Measurement of TCP traffic between nodes

[Mikhail Kuzminsky]

            Dear colleagues,

I want to measure message sizes (and "frequencies" of messages
exchanges) between cluster nodes under parallelization of
some applications. These applications use parallelization tools
working over TCP (Linda, DDI), so I need to know the size of TCP 
packages and the number of TCP packages per second.

1) There is no other traffic on the corresponding interfaces,
and (at least for 2-nodes "subcluster"; it's used for simplicity) I 
may use simple ifconfig output (in a loop). Do I understand correctly, 
that
the number of bytes transmitted at "application level" is
something about (for example for transmission)
Tx_bytes - TX_packets*40    ?
(i.e. a) there is no bytes from ethernet headers - in ifconfig output
       b) the number of application transmitted bytes per TCP packet = 
 
          size_of_packet - 40 (in average))

2) Are the tools like tcpdump better for this task (pls
take into account that I need only timestamps and data sizes) ?


Yours
Mikhail Kuzminsky
Zelinsky Institute of Organic Chemistry
Moscow