sub process_sip {
    my ($user_data, $header, $packet) = @_;
    my $asccidata = substr($packet,42);
    my $sip_pkt = Net::SIP::Packet->new_from_string($asccidata);
    my $callid=$sip_pkt->get_header('call-id');
    if (exists $main_hash{$callid}) {
 ...