reply function 
 
    
        
void
reply(
 - int status_code
) 
    
    
  Implementation
  void reply(int status_code) {
  List<dynamic> vias = message.getHeaders('via');
  dynamic to;
  String response =
      'SIP/2.0 $status_code ${DartSIP_C.REASON_PHRASE[status_code]}\r\n';
  for (dynamic via in vias) {
    response += 'Via: $via\r\n';
  }
  to = message.getHeader('To');
  if (message.to_tag == null) {
    to += ';tag=${Utils.newTag()}';
  }
  response += 'To: $to\r\n';
  response += 'From: ${message.getHeader('From')}\r\n';
  response += 'Call-ID: ${message.call_id}\r\n';
  response +=
      'CSeq: ${message.cseq} ${SipMethodHelper.getName(message.method)}\r\n';
  response += '\r\n';
  transport.send(response);
}