code: private void sendGenericNack(Pdu packet){
  		
  		GenericNack genericNack = new GenericNack();
  		genericNack.setSequenceNumber(packet.getSequenceNumber());
  	    genericNack.setCommandStatus(SmppConstants.STATUS_INVCMDID);
  
  		ChannelBuffer buffer = null;
  		try {
  			buffer = transcoder.encode(genericNack);
  			
  		} catch (UnrecoverablePduException e) {
  			logger.error("Encode error: ", e);
  		}catch(RecoverablePduException e){
  			logger.error("Encode error: ", e);
  		}
  		
  		if(logger.isDebugEnabled())
  			logger.debug("LB sent generic_nack response for packet ("+ packet +") to " + channel.getRemoteAddress().toString() + ". session ID : " + sessionId);
  		channel.write(buffer);
  	}
docs: Send generic_nack to client if unable to convert request
  from client
  @param packet PDU packet