There are other Tunnels but below will only cover the p2p ME tunnel!
P2p tunnels have a few uses, as a rule of thumb remember that you can only have one input and up to 4 outputs, this will make more sense later but should be kept in mind and goes for all P2P tunnels.
Each controller is able to provide 32 channels, the only way to access these 32 channels is with a dense cable. We can use normal cables but these will only carry up to 8 channels. Now if you need 16 channels at the other end of your base it would need 1 dense cable per bock. We can reduce the cost of this with p2p tunnels.
We can attach a p2p tunnel to the controller, then we can run normal 8 channel cable (whatever is cheapest) to whatever location of our base, at the other end we can attach another p2p tunnel. Before we can link these tunnels up we need to give the p2p tunnels power. If power is attached to the controller it will not give any power to tunnels that are attached to it. We can use a energy converter or if you already have powered your controller normal cable and quartz cable:
Now that the 2 tunnels have how we can link them with a network card. We need to set one as a input, this input would be the p2p channel attached to the controller, we are inputting 32 channels. We also need to have an output or an exit for these channels, this would be the 2nd p2p you put down.
Once linked you can start using a dense cable on the 2nd p2p tunnel, this dense cable will have 32 channels that are being provided by the controller.
Each network can also only have one controller, this means if you have already used up each face of the controller with cables and the only way to increase the amount of channels is to use more controllers. Remember not to break the rules surrounding controllers.
When using a controller it's a very good idea to use different coloured cables for each face, this way you can dedicate a certain colour to just a certain part of your base. The only limiting factor to the Controller is how many cables you can attach to it. Having a huge controller with more than 17 faces can get very messy very quickly:
The controller already has 16 different coloured cables, if you continue with this set up you will cross cables and could risk your whole system crashing. This is also very expensive, dense smart cables require a bunch of materials and when you need more than 2 faces and your controller is far away the costs stack up.
This is where P2P tunnels come in, this essentially lets you move the 32 channels from the controller ro wherever you want and compress it into one channel.
Using one controller we can move 160 channels (5 faces / 32) through one normal Smart Cable (5 Channels one for 3 each p2p tunnel). This would make it easier to manage your network and would cost significantly less). In the below example we are attaching 5 p2p tunnels to 5 faces of the controller.
The last space on the controller has a dense smart cable attached, attached to the dense cable are normal smart cables coming from each p2p tunnel into the controller, since each p2p channel needs a channel to work. We are using one face (32 channels) for P2P tunnels, we can have up to 32 p2p tunnels attached to this face.
Next we need to power the controller, with no power there are no channels. We can connect a smart cable to the dense cable (which is going directly to the controller face) and we can plop down an energy acceptor along with an energy source of your choosing or an energy cell. This should power the controller and make it glow. The energy acceptor will not take up a channel, this will just provide power to the network. We can see that we are using one face (the one without a p2p tunnel) to provide channels for our p2p tunnels, as we are powering cables that directly attaches to a face of the controller and to each P2P tunnel everything will always have power.
We can carry on this smart cable (the black “flux” cable) to 5 different points, we can colour code each point to make it easier to manage the network. If we go back to the controller and have 1 single coloured smart cable coming off each p2p tunnel (each tunnel should use a different colour) and connect them all together with a Smart Cable Fluix, this will help us when connecting the tunnels together.
We can run this smart cable as far as we want, we can then attach a new p2p tunnel and connect it with the other p2p tunnel of your matching colour (This example will use red). Shift-RIght click the red p2p tunnel on the controller and then use the card by right clicking on the destination p2p tunnel. Coming out of this p2p tunnel should be a dense cable, now you can start connecting up to 32 machines to this cable with normal smart cables.
We can do the above process for every colour, Red, Blue, Green, Orange, Pink. This will give us a total of 160 machines on this one network and they can all talk to each other! The main smart cable running to the 5 p2p tunnels and ending into the dense smart cable that is attached to the controller will have 5 channels used since we have 5 p2p tunnels attached, within these 5 tunnes we have 160 channels compressed!
We have also saved a bunch of materials by only using a few dense cables. You can of course run dense cables directly from the controller but this could be very expensive. This can also be made cheaper by using normal cables rather than smart cables.
If your controller is 100 blocks underground you will be running a whole bunch of dense cables at least 100 blocks if you only use one channel.
Now this is ONE controller, adding another controller would push this number up to 288 and 2 to 416 and so on, it goes to prove that you don't need a ton of controllers.