Here is a possible main loop:

my %needed_transaction;
while (my %record = get_record()) {
  if ($record{CALL_INIT}
    and $record{CHAN_TYPE} =~ /TCH/
  ) {
    $needed_transaction{ $record{TRAN_ID} } = 1;
  }
  elsif ($record{CALL_RESPONSE}
    and $needed_transaction{ $record{TRAN_ID} }
  ) {
    output_record(%record);
    delete $needed_transaction{ $record{TRAN_ID} };
  }
}
[download]

The get_record function should read one block (up to the equals signs) and return a list of key/value pairs. The output_record function should pass along your Px, Py pair. I'll leave those to you to code.

Personally I would pass around anonymous hash references rather than hashes, but I don't know if you know about references. If you want to try that, a good starting point is references quick reference. But as I say, you don't need to go that route to get a working solution.