Hi, no the line 89 is: 0x00000015 => { cmd => 'enquire_link', The reply_tab is a sub that process the PDU in case of match send a reply to PDU use constant reply_tab => { 0x80000000 => { cmd => 'generic_nack', reply => undef, }, 0x00000001 => { cmd => 'bind_receiver', reply => sub { my ($me,$pdu) = @_; $me->set_version(0x34); $me->bind_receiver_resp(system_id => $sysid, seq => $pdu->{seq}); . . . . 0x00000015 => { cmd => 'enquire_link', reply => sub { my ($me, $pdu) = @_; $me->enquire_link_resp(seq => $pdu->{seq}) }, }, . . .} Reply_tab do not return the correct answer...