#!/usr/bin/perl

# Name:
#       Tweak
#       Tweak parameters to tune tcp buffers
#
# Author:
#       Börje Josefsson <bj@sunet.se>  2003-03-04
#
# Function:
#       Calculate RTT, and compute buffer size needed for TCP
#
# Revision history:
#       Date            Who             Comment
#       2003-03-04      bj@sunet.se     Initial version
#
# Parameters:
#       -v      Verbose
#       -s      Set values locally
#       -b      Bandwidth (in Mbit/sec)
#       -d      Duration of ttcp test (in seconds)

##########
# Initializion values
##########

$numpings = 4;                     # Number of pings per probing
$buflen   = 61440;                 # 15 * pagesize on FreeBSD

require "getopts.pl";
&Getopts('vsb:d:') || die "Illegal option(s), see manual!\n";

###############
# Main program
###############

$server   = $ARGV[0];
$verbose  = $opt_v;
$bitrate  = $opt_b;             # in Mbit/sec
$duration = $opt_d;

$duration = 10 if ($duration < 10);
$duration = 60 if ($duration > 60);
$bitrate  = 10 if ($bitrate < 10);
$bitrate  = 2000 if ($bitrate > 2000);

&ping;

$buf=($RTTmax/1e+3) * $bitrate * 1e+6/8;    # bitrate -> bytes/sec * RTT
$mbuf=$buf/(1024*1024);

printf "RTTmax = %5.2f ms. Buffer size needed = %d bytes (%5.2f Mbytes)\n\n", $RTTmax, $buf, $mbuf;

$buf = int($buf * 1.25);      # Add 25% just in case...

print "The following settings can be used on the remote system:\n";
print "\tSyntax for NetBSD/FreeBSD, Your mileage may vary...\n\n";
print "sysctl -w net.inet.tcp.sendspace=$buf\n";
print "sysctl -w net.inet.tcp.recvspace=$buf\n";
print "\n\n";

if ($opt_s) {
  system "sysctl net.inet.tcp.sendspace=$buf";
  system "sysctl net.inet.tcp.recvspace=$buf";
}

$bytes_to_send = (($bitrate * 1e+6) / 8) * $duration;
$numbufs = int ($bytes_to_send / $buflen);

print "\tTTCP parameters, calculated for $duration seconds on $bitrate Mbit/sec:\n";
print "Sender:\n"; 
print "ttcp -s -t -f m -l $buflen -n $numbufs $server\n";
print "Receiver:\n";
print "ttcp -s -r -f m -l $buflen -n $numbufs\n";

###############
# Subroutines
###############

sub ping {
# Run 'ping' to calculate RTT
  print "RTT ping start\n" if $verbose;
  foreach (`/sbin/ping -n -q -c $numpings $server`) {
# Note - command syntax for FreeBSD, needs to be tweaked for other OS:es!!
    if (/^round-trip.*= (.*)\/(.*)\/(.*)\/.* ms/) {
      $RTTmin    = $1;
      $RTTavg    = $2;
      $RTTmax    = $3;
      $RTT    = sprintf "%5.2f/%5.2f/%5.2f", $RTTmin, $RTTavg, $RTTmax;
    }
  }
  print "RTT ping finished = $RTT\n" if $verbose;
}