For a start the horrible nested if/else if code in the for loop can be cleaned up by using elsif (which you actually use in the while loop!):

foreach (@data) {
    my %ipstn_s;
    my %ipstn_a;

    next if $_->{_status} eq 'STOP';

    if ( $_->{_status} eq 'START' && $_->{_i_pstn_trunk} ) {
        my $i_pstn_si = extract( $_->{_i_pstn_circuit}, $_->{_i_pstn_t
+runk} );
        push @{ $ipstn_s{$i_pstn_si} }, $_;
        pushnow( \%ipstn_s );
    } elsif ( $_->{_status} eq 'START' ) {
        my $e_pstn_se = extract( $_->{_e_pstn_circuit}, $_->{_e_pstn_t
+runk} );

        ...

        pushnow( \%ipstn_a );
    } else {
        $ncounter++;
    }
}
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Note too that $counter has been removed - it should be identical with @data used in scalar context. Also the next is handled by an if modifier which removes another level of indentation.