my @ids;
my $t = XML::Twig->new();
$t->parse($xmlStr);
for my $one ($t->root()->children('one')) {
    if ($one->first_child('traffic')->first_child('monthly')->att('value') eq 'on') {
        push @ids, $one->att('id') 
    }
}
print Dumper(\@ids);

__END__

$VAR1 = [
          'movies',
          'espn'
        ];