$6 !~ /^ack/ && $5 !~ /[SFR]/   {
       # given a tcpdump ftp trace, output one line for each send
       # in the form
       #   <send time> <seq no>
       # where <send time> is the time packet was sent (in seconds with
       # zero at time of first packet) and <seq no> is the tcp sequence
       # number of the packet divided by 1024 (i.e., Kbytes sent).
       #
       # convert time to seconds
       n = split ($1,t,":")
       tim = t[1]*3600 + t[2]*60 + t[3]
       if (! tzero) {
               tzero = tim
               OFS = "\t"
       }
       # get packet sequence number
       i = index($6,":")
       printf "%7.2f\t%g\n", tim-tzero, substr($6,1,i-1)/1024
       }