Fighting with computers

In the past I tried a Bluetooth link for sending g-code wirelessly to a 3D printer. It works ok but it seems a bit slow so eventually small stops happen while printing (buffer empties). Wifi was an expensive option at the time so I forgot about it. Recently, the availability of the excellent ESP-link firmware together with NodeMCU/ESP12E boards for less than $5 painted a different scenario and while I was not on an immediate need of it I decided to give it a try during my summer holidays. That firmware could be used with smaller and cheaper ESP8266 boards but I have found much more convenient to use (as they include their own voltage regulator) the so-called Nodemcu, just $1 more or so. These boards pack a 32bit SoC with 4Mbytes of flash and, lately, they are even supported through the Arduino IDE. In order to keep the printer still usable through USB connected to a computer I patched Marlin so I could use an additional serial port for the wifi connection. The problem was that

I was recently ask by a friend about how certain P2P wireless cameras can be accessed from a cellphone with no router configuration. I had no idea about those cameras or its so-called P2P-thing whatever that was that tricked your home router so your camera can be accessed using a mobile app. Of course if both the wifi camera and the cellphone belong to the same LAN there is a simple answer, but when they belong to different networks and there are one or more routers in between things may get murkier, specially when one or more of these routers are broadband routers (marketing-talk for NAT boxes). The problem of reaching one host on the Internet from another is: to figure out its IP address to be able to connect to it (this is where firewalls may be a problem for your communication) However, if a device is connected to a home network with Internet access, it is most likely served by one of these broadband routers, that will block any connection attempt that might come from