 In the early 1800s, or I guess in this case in exactly 1800, Alessandro Volta invented the first electric battery. And within a fairly short period of time, so by 1830s, electric power was a very common power source, both in industrial and household applications, which in turn led to another very important invention. So by about 1845 or 1840s, we started seeing electric telegraphs. And nowadays, we drop the electric part and simply refer to it as the telegraph. And once it arrived, the visual telegraph dramatically changed how we communicate with each other. Recall that up until this point, the fastest way to deliver a message was through the use of a visual telegraph, which used semaphores. So we had a building and we had these big mechanical arms to communicate different letters of the alphabet. And the visual telegraph has a couple of important properties. First of all, it is fast because it is delivering messages with the speed of light between the stations. But the downside is that we needed many of these stations along the way because they would need to be in line of sight. So because of that, it was very expensive and it was also not very reliable, to be honest, because at night, of course, we couldn't see these signals. Now, let's compare this to the electric telegraph. So to send a message with the electric telegraph from point A to point B, we would need a cable, something like a copper cable between A and B to send our electric signals. And the difference is that unlike the visual telegraph, which would need many different stations along the way, the copper cable could carry our signal anywhere from tens to even thousands of kilometers without the need for any of these repeat stations, which meant that it actually became a lot cheaper to send messages. And perhaps even more importantly, it was still very fast. It turns out that messages or electric signals when they're sent over this copper cable still travel with the speed of light, a little bit slower because they're traveling through copper, but nonetheless, very, very fast. And because of these two properties, the electric telegraph replaced the visual telegraph very quickly. To the point that by 1861, we already had a transcontinental line within the United States, which meant that we had tens of thousands of kilometers of this copper cable laid within just about 15 years. Now, here's an interesting question and that is how exactly do we communicate over this copper cable? Because recall that the only thing we can send is just this electric signal. So either we are sending the signal, which means it's on, or there is no signal, in which case it's off. So we only have these two modes. And that is where Samuel Morse comes in. And of course, he's very well known for the Morse code. And the system he came up with is actually very clever. So he used two things, dots and dashes. And a dot over this copper cable is just a short signal. So for example, if we were to send our electric signal for a period of one second, we could call that a dot. Whereas a dash could be a longer signal. So for example, three seconds. And using these two things, we can encode the entire alphabet and transmit any message that we want. So for example, the letter A could be encoded as a dot followed by a dash. The letter E could be just a dot. And the letter T is represented by a dash. So if we wanted to send a message, let's say EAT using the Morse code, that would actually just be a dot, which stands for letter E, followed by letter A, which is a dot and a dash, and another dash for the letter T. And once we had the Morse code, and because it was so much cheaper to transmit messages over these copper cables, communities all over the place started connecting with each other. So for the first time, we started seeing these networks emerge. And the popularity of the electric telegraph created a new problem, which we haven't seen before, which is network congestion. So let's take a closer look. Recall that every message system has a number of delays. And in our case, we want to transfer a message from A to B over a copper cable. And because these are electric signals, the propagation delay is actually going to be, or the speed with which they will travel is 300,000 kilometers per second. So very fast. But on both ends of this cable, we have our human operators. And it turns out that a fast operator when working with Morse code could process about 40 words per minute, which also means that the maximum data rate of this link here is about 40 words per minute. Now, what if we actually want to transfer 80 words per minute? We can't make the operator go any faster. So one simple solution is, of course, to have another cable. And that's exactly what happens. So now we have multiple cables between these two points and we can transfer multiple messages at the same time. But while this solves one problem, it actually creates a number of other problems. And to see why, let's imagine we are inside one of these telegraph offices. We have multiple lines coming in. So here's our first receiver and we have a second receiver. And in fact, we want to route messages to multiple destinations. So we'll need multiple cables for that as well. And just to make this whole process faster, we'll employ multiple senders. So sender one and sender two. And now that we have multiple receivers and senders, whenever a new message comes in, we actually need to figure out where we want to route it to, which sender, either C or D, which introduces a new type of delay, which is a routing delay, where we need to examine where the message needs to go to and also deliver it to the right location. But there's also another delay, which is let's imagine that both of the receivers are working at full speed receiving messages. And both of them want to send messages to destination D, which means that this guy right here, even if he transmits at full speed, won't be able to keep up with both of these receivers. And that is our queuing delay, which is the time that the message will spend waiting in this queue. And it turns out that in the early days of the telegraph, it was actually the processing and the queuing delays, which were responsible for the network congestion. And in turn, a lot of the early innovation in the electric telegraph space was actually around process innovation, where the focus was on making these offices more efficient to minimize these routing and queuing delays because they were the major sources of latency, which is of course very interesting because conceptually this diagram right here is no different than a modern internet router where you have multiple packets coming in, we need to figure out where to route them to and then minimize all of the possible delays.