What should be the way to design code for such a situation?

Question

I have a graph as given below:

Let us assume one node as transmitter and another as receiver.

1. We need to transfer particles in every time slot constrained by maximum particles N and minimum 0. The combination of which particle in which time slot makes a code. I mean if 2 1 0 0 is a code that means that 2 particles in slot zero 1 in slot 1 and 0 particles in slot 2 and 3
2. Now let us suppose that any particle in a time slot can take any path and suffer through at most K delays. Delays are given by number of dots. More dots more delay. The delay to particles can be assigned randomly. The maximum delay for this graph is 4 it can be generalized to K. How to design codes so that information is reliably transferred across transmitter and receiver.

I just want to know how these codes are constructed, assuming that other codes must exists to be revealed. Also please tell me the prerequisites I need for such problem as I am not a computer engineer. One way is given in here