In this post we will explain what is a deterministic network and why they are used inside the aircrafts.
A deterministic network is not called like this by chance. Determinism according to the Oxford dictionary means “the doctrine that all events, including human action, are ultimately determined by causes external to the will”. Obviously this definition is not applied to the networks, otherwise to humans but, we could say that translated to the network language means: a network in which you always know from where and to where you are receiving and sending the data. Thus, flexibility is not permitted while connecting devices or changing features, everything must be known and controlled while sending and receiving information. For example, imagine we have an office and we have just bought a switch to connect some computers. In most of the cases, that switch will have a default configuration, ports enabled automatically when connected, dynamic forwarding tables (directions used by the switch to commute through the right port), … This means, first we buy a switch, second we connect it directly to a computer and it works! We could affirm that this is the opposite of a deterministic network. In a deterministic network we cannot connect a computer to any port, we are obliged to do it to the port configured for that computer. With the forwarding tables we have a similar issue, we cannot let them configured dynamically but in a static way. For instance, the income port 1 of the switch will always go through the output port 2 and this will be always like this, no changes will be happen.
Apparently we can think that no advantages are shown in these kind of networks but there really exist. Let’s think about an aircraft, as we can imagine, chance is the last thing we want to find there, terrible consequences could occur if we do it. So, everything must be perfect and statically configured. This is the main reason why deterministic networks are used inside aircrafts and a perfect example of that is AFDX.