Hello everyone. My name is Peter Stutz. I'm professor of aeronautical engineering at the University of the Armed Forces in Munich. Today I'm going to talk to you about digital avionics networks. So the first question that arise is, what are avionics? It's very simple actually. It's an artificial and mixed word comprised of aviation and electronics. So it actually means all electronic equipment on board of the aircraft. Again, today we talk about digital avionics networks. So first I'll give you some basic ideas about networking technologies and then lead you into three examples of existing networking technologies. This will be the ARINC 429, the Mil-standard 1553 or also called Mil-BUS, and the ARINC 664 AFDX. So since the invention of aircraft, it was always the goal to assemble information and to sample data on various points of the aircraft, on certain aircraft state variables, on the state of certain aircraft systems and relay this information to parties who are interested in that data. Usually, that data sampling was achieved by having sensors such as, for example, if you want to measure altitude or airspeed, you need to have some pressure measuring devices at certain parts of the aircraft and then the data was then relayed, for example, to instruments in the cockpit and displayed to whoever is interested in that case, let's say the flight crew and the presentation of the data was done via analog instruments. Actually, the whole data processing or data transmission was analog. Analog, in this case, means that, well, analog voltage values, for example, were transmitted via a standard copper wire and then put on some analog display or instrument. The problem with that was that this data sampling and information transmission added additional weight and complexity to the overall aircraft system. In the '60s and '70s, the idea was born, why not having a common media to communicate with? The same time, digital data processing came up and we all know that. We all have our experiences by now with that in our everyday life using our computers, using our smartphones, using the Internet and the web, all that ideas then came into the aircraft by using digital avionics networks. The most important point of this idea is so that now several components use the same media to communicate with. We see that in the lower part of the slide, where you'll see a well-networked component system, which we now call the digital avionic network. In the community, it's also called the avionics BUS. BUS here doesn't stand actually for the vehicle, it's an abbreviation, it stands for binary unit system. So as said, the goal of avionic networks is to enable communication between digital IT components. I already mentioned some of those components. Those may be sensors, computers, displays, actuators, just to name a few. There are specific requirements we put on this networks. First, it's quite self-understanding, I guess. High data rate, and now comes something that's really airborne-specific, high-reliability, integrity, real-time capability, and deterministic behavior. In terms of safety-critical systems, we have a couple of those on board of aircraft, it's very important that those networks work reliable and in integer way. We think that the failure of that networks might cause the loss of life because certain systems, if they fail, would lead to an aircraft crash or accident. Now, on to some more basics. Let's talk about transmission modes. In the easiest way, we talk about simplex systems or simplex transmission. Please imagine a regular radio broadcast station. Here, one entity, or the broadcast station itself, communicates to a receiver, just some people having a radio with them. So here the communication is only one way and there is no way for entity two. If you have a look at the slide in the upper part, can come back to entity one. If you want to achieve that, both way communication, we have to go into duplex transmission modes. Also, here we can discriminate between half-duplex and full-duplex. Half-duplex uses the same channel, the same media, however, only one sender at a time can send a message. So if entity number 2 wants to send the message back to number 1, it has to wait until one has sent its message and the message is processed. So no simultaneous transmission of message is allowed on half-duplex transmission. If you want to achieve a simultaneous transmission, then we need to have full-duplex transmission mode. These usually requires a separate channel for sending in any direction or a very sophisticated way of managing messages on one single channel. The problem with using a single channel for both way simultaneous communication is that it would lead to collisions on the wire if two messages more or less meet during their travel through the wire and therefore usually gets either eliminated or garbled. Another thing we should talk about is topology. Here in that slide, you'll see four types of topologies. On the upper left, you see the star topology. Its unique feature s a centerpiece, which we use to call either switches or router. We all know that because that kind of topology is what we usually have also in our homes, in our offices. The switches are those we connect our computers, our laptops to if we have a wired connection, or email wireless connection, although that would connect directly to that central component. So that's the star topology. It can be even more complex. So we can form hierarchical architectures from star topologies and then with that, create tree topologies, which is symbolized on the upper-right. Another way to interface those different networked components is the linear topology, which you see on the lower left. Its feature is the actual backbone media where all computer components connect to. Of course, again, if that fails, similar to the switch in the star topology, then the network would go down. A fourth topology type is the ring topology. It's for mere completion actually, it displayed here. It doesn't have a great meaning in the world of avionics. However, star and linear topologies, we will come back to that just in a few minutes. Now, a word to the actual transmission media. For now, we do not have a widespread usage of wireless communication in aircraft. Usually, we have wired, cabled networks and it's wise to mention two important attributes of those cabling, and it's all about how to prevent interference with other networks, other components, other electronic devices. First, that's what you see in the upper part is we are using a twisted-pair wires which are shielded. [inaudible]. First, we're using twisted paired wires which are shielded. The twisting helps us to accept interference and disturbing signals from the outside in an equalized manner on both wires. With that, it's easier for us to eliminate actually those disturbances later on. The shielding, well, prevents the input of outside interferences just into the wire pair. The second part I would like to mention is symmetric signaling. So again, think of the wire pair. We need to, well, bring on a certain wavefront that's traveling here to transmit that. It's not that one wire just carries the reference mass and the other wire carries information signal. Now, we're doing it a little bit more complicated. We have the signal wavefront going on one cable. Sorry, it's different. We are having the signal front on one wire traveling as it is designed, and having the same signal, but just inverted on the other wire. With that mechanism, we help to prevent interference to other circuits. On the lower right, you see two different ways of such symmetric signaling which are used on digital avionic networks. Now, last within the section of giving some basic ideas, is what a generic network would look like in a linear topology. Again, you would see here the backbone consisting of twisted-pair wire, you would see is several avionics components which would like to communicate with other. Here they are called avionics LRUs, a very common abbreviation again, and LRU stands for line replaceable unit. I think that every avionics engineer, once in his lifetime, will deal with that abbreviation.
