The Internet is a vast and diverse place. Not only is it huge, the number of different devices connected to it can be just as staggering. And if we were to actually describe all these devices, they'd have an almost endless number of functions. The devices that connect to the Internet fall into familiar silos; desktop and laptop computers, servers and data centers, routers and switches that direct network traffic etc. But this list also includes things like; tablets and cell phones, ATMs, industrial equipment, medical devices and even some cars are now connected to the Internet. The list go on and on. It's nice and simple to discuss everything in terms of a basic physical layer made up of Cat5 or Cat6 cables and a data link layer made entirely of Ethernet. But that's not exactly how things work when they actually connect to the Internet. The technologies used to get people and devices connected are as different as the people and devices themselves.
As computer use grew over the course of the 20th century, it became obvious that there was a big need to connect computers to each other so that they could share data. For years before Ethernet, TCP, or IP were ever invented, there were computer networks made up of technologies way more primitive than the model we've been discussing. These early networking technologies mostly focused on connecting devices within close physical proximity to each other. In the late 1970s, two graduate students at Duke University were trying to come up with a better way to connect computers at further distances. They wanted to share what was essentially bulletin board material, then a light bulb moment went off. They realized the basic infrastructure for this already existed, the public telephone network. The public Switched Telephone Network or PSTN is also sometimes referred to as the Plain Old Telephone Service or POTS. It was already a pretty global and powerful system by the late 1970s more than 100 years after the invention of the telephone. These Duke grad students weren't the first ones to think about using a phone line to transmit data. But they were the first to do it in a way that became a somewhat permanent precursor to the dial-up networks to follow. The system they built is known as USENET and a form of it is still in use today.
At the time, different locations, like colleges and universities, used a very primitive form of a dial-up connection to exchange a series of messages with each other. A dial-up connection uses POTS for data transfer and gets its name because the connection is established by actually dialing a phone number. If you use dial-up, back in the day, this noise might sound familiar to you. It was like nails on a chalkboard as we waited to get connected to the Internet for some of us. Transferring data across a dial-up connection is done through devices called modems.
Modem stands for modulator-demodulator, and they take data that computers can understand and turn them into audible wavelengths that can be transmitted over POTS. After all, the telephone system was developed to transmit voice messages or sounds from one place to another. This is conceptually similar to how line coding is used to turn ones and zeroes into modulating electrical charges across Ethernet cables. Early modems had very low baud rates. A baud rate is a measurement of how many bits could be passed across a phone line in a second. By the late 1950s, computers could generally only send each other data across a phone line at about 110 bits per second. By the time USENET was being developed, this rate had increased to around 300 bits per second. And by the time dial-up access to the Internet became a household commodity in the early 1990s, this rate had increased to 14.4 kilobits per second. Improvements continue to be made, but widespread adoption of broadband technologies. Dial-up Internet connectivity is pretty rare today but it hasn't completely gone away. In some rural areas, it might be the only option still available.
The term broadband has a few definitions. In terms of internet connectivity, it's used to refer to any connectivity technology that isn't dial-up Internet. Broadband Internet is almost always much faster than even the fastest dial-up connections and refers to connections that are always on. This means that they're long lasting connections that don't need to be established with each use. They're essentially links that are always present. Broadband shaped today's world. While the Internet itself is a totally amazing invention, it wasn't until the advent of broadband technologies that its true potential for business and home users was realized. Long before people had broadband connections at home, businesses spent a lot of resources on them usually out of necessity. If you had an office with more than a few employees, the bandwidth available by a single dial-up connection would quickly be oversaturated by just a few users. By the mid 1990's, it had become pretty common for businesses that needed internet access for their employees to use various T-carrier technologies. T-carrier technologies were originally invented by AT&T in order to transmit multiple phone calls over a single link. Eventually, they also became common transmission systems to transfer data much faster than any dial-up connection could handle. After businesses got into the broadband game, home use became more prevalent. As different aspects of the Internet, like the World Wide Web became more complex, they also required ever increasing data transfer rates.
In the days of dial-up, even a single image on a web page could take many seconds to download and display. High-resolution photos that you can now take on a cell phone would have required a long time to download and a lot of your patience. A single picture taken on a smartphone today can easily be several megabytes in size. Two megabytes would translate to 16,777,216 bits. At a baud rate of 14.4 kilobits per second, that many bits would take nearly 20 minutes to download. Without broadband internet connection technologies, the Internet as we know it today wouldn't exist. We wouldn't be able to stream music, or movies, or easily share photos. T-carrier technologies require dedicated lines, which makes them more expensive. For this reason, you usually only see them in use by businesses. But other broadband solutions also exist for both businesses and consumers. Four of the most common broadband solutions available today: T-carrier technologies, digital subscriber lines or DSL, cable broadband, and fiber connections.
T-carrier technologies were first invented by AT&T in order to provide a system that allowed lots of phone calls to travel across a single cable. Every individual phone call was made over individual pairs of copper wire before Transmission System 1, the first T-carrier specification, called T1 for short.
With the T1 specification, AT&T invented a way to carry up to 24 simultaneous phone calls across a single piece of twisted pair copper. Years later, this same technology was repurposed for data transfers. Each of the 24 phone channels was capable of transmitting data at 64 kilobits per second, making a single T1 line capable of transmitting data at 1.544 megabits per second. Over the years, the phrase T1 has come to mean any twisted pair copper connection capable of speeds of 1.544 megabits per second, even if it doesn't strictly follow the original Transmission System 1 specification.
Originally, T1 technology was only used to connect different telecom company sites to each other and to connect these companies to other telecom companies. But with the rise of the Internet as a useful business tool in the 1990s, more and more businesses started to pay to have T1 lines installed at their offices to have faster Internet connectivity. More improvements to the T1 line were made by developing a way of multiple T1s to act as a single link. So a T3 line is 28 T1s, all multiplexed, achieving a total throughput speed of 44.736 megabits per second.
You'll still find T-carrier technologies in use today, but they've usually been surpassed by other broadband technologies. For small business offices, cable broadband or fiber connections are now way more common since they're much cheaper to operate. For inter-ISP communications, different fiber technologies have all replaced older copper-based ones.
The public telephone network was a great option for getting people connected to the Internet since it already had infrastructure everywhere.