private void reply_if_isACK(Packet packet)
	{
		
		TransportLayer tl = packet.getTransport();
		if (tl instanceof TCP)
		{
			TCP transport = (TCP) tl;
			if (transport.isACK())
			{		
				Packet ack_packet = new Packet("TCP");
				ack_packet.setIP_source(this.computer_ip);
				ack_packet.setIP_destination(packet.getIP_source());
				
				TCP ack_transport = new TCP(transport.getDestination_port(), 
						transport.getSource_port());
				
				//determina o offset numa transferência de arquivos
				int next_offset = transport.getACK_number();
				if (next_offset > 1)
				{
					next_offset = transport.getSequence_number() + 1460;
					this.data_offset = next_offset;
				}
				ack_transport.setSequence_number(transport.getACK_number());
				ack_transport.setACK_number(next_offset);
				if (transport.isFIN())
					ack_transport.setFIN(true);
								
				ack_packet.setTransport(ack_transport);
				send_packet(ack_packet);
			}
		}
		
	}