Something like:

use strict;
use warnings;
my %hash = ();

for (<DATA>) {
  chomp;
  my ($day, $ip, $i, $j) = split(q{,}, $_);
  $hash{$day}{$ip}{i} += $i;
  $hash{$day}{$ip}{j} += $j;
}

foreach my $day (sort keys %hash) {
  foreach my $ip (sort keys %{$hash{$day}}) {
    print qq{$day,$ip,} .
      $hash{$day}{$ip}{i} . q{,}.
        $hash{$day}{$ip}{j};
  }
}

__DATA__
01 Jul 2007,221.6.19.196,9,19
01 Jul 2007,221.6.19.197,1,3
01 Jul 2007,221.6.19.196,12,12
01 Jul 2007,221.6.19.197,2 ,2
02 Jul 2007,202.119.104.22,1,1
02 Jul 2007,221.6.19.196,20,45
03 Jul 2007,202.119.104.12,1,11
03 Jul 2007,202.119.110.236,1,2
03 Jul 2007,210.29.132.9,1,2
03 Jul 2007,210.29.141.188,1,2
03 Jul 2007,221.6.19.195,3,7
03 Jul 2007,221.6.19.196,4,7
03 Jul 2007,222.192.2.213,1,0
03 Jul 2007,202.119.108.42,3,3
[download]

$ perl -l 637112.pl
01 Jul 2007,221.6.19.196,21,31
01 Jul 2007,221.6.19.197,3,5
02 Jul 2007,202.119.104.22,1,1
02 Jul 2007,221.6.19.196,20,45
03 Jul 2007,202.119.104.12,1,11
03 Jul 2007,202.119.108.42,3,3
03 Jul 2007,202.119.110.236,1,2
03 Jul 2007,210.29.132.9,1,2
03 Jul 2007,210.29.141.188,1,2
03 Jul 2007,221.6.19.195,3,7
03 Jul 2007,221.6.19.196,4,7
03 Jul 2007,222.192.2.213,1,0
[download]

Update: Renamed variables from $a, $b to $i, $j as adviced by GrandFather.