Broadband Connections
Table of Contents
- What is broadband?
- T-Carrier Technologies
- Digital Subscriber Lines
- Cable Broadband
- Fiber Connections
What is broadband?
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. We'll cover the details of T-carrier technologies in an upcoming lesson. 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.
No one would've had time to download all the hilarious cat images on the internet back then. What a travesty. 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. You definitely couldn't be taking an online course like this. 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. In the next few videos, we'll deep dive into 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
T-carrier technologies were first invented by AT&T in order to provision 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.
Digital Subscriber Lines
The public telephone network was a great option for getting people connected to the Internet since it already had infrastructure everywhere.
For a long time, dial-up connections were the main way that people connected to the Internet from home. But there were certain limitations with trying to transmit data as what were essentially just audio waves. As people wanted faster and faster Internet access, telephone companies began to wonder if they could use the same infrastructure but in a different way.
The research showed that twisted pair copper used by modern telephone lines was capable of transmitting way more data than what was needed for voice-to-voice calls. By operating at a frequency range that didn't interfere with normal phone calls, a technology known as digital subscriber line or DSL was able to send much more data across the wire than traditional dial-up technologies. To top it all off, this allowed for normal voice phone calls and data transfer to occur at the same time on the same line.
Like how dial-up uses modems, DSL technologies also use their own modems. But, more accurately, they're known as DSLAMs or Digital Subscriber Line Access Multiplexers. Just like dial-up modems, these devices establish data connections across phone lines, but unlike dial-up connections, they're usually long-running. This means that the connection is generally established when the DSLAM is powered on and isn't torn down until the DSLAM is powered off. There are lots of different kinds of DSL available, but they all vary in a pretty minor way. For a long time, the two most common types of DSL were ADSL and SDSL.
ADSL
ADSL stands for Asymmetric Digital Subscriber Line. ADSL connections feature different speeds for outbound and incoming data. Generally, this means faster download speeds and slower upload speeds. Home users rarely need to upload as much data as they download since home users are mostly just clients.
For example, when you open a web page in a web browser, the upload or outbound data is pretty small. You're just asking for a certain web page from the web server. The download or inbound data tends to be much larger since it'll contain the entire web page including all images and other media. For this reason, asymmetric lines often provide a similar user experience for a typical home user, but at a lower cost.
SDSL
SDSL, as you might be able to guess, stands for Symmetric Digital Subscriber Line. SDSL technology is basically the same as ADSL except the upload and download speeds are the same. At one point, SDSL was mainly used by businesses that hosted servers that needed to send data to clients. As the general bandwidth available on the Internet has expanded and as the cost of operation have come down over the years, SDSL is now more common for both businesses and home users. Most SDSL technologies and have an upper cap of 1.544 megabits a second or the same as a T1 line.
Further developments in SDSL technology have yielded things like HDSL or High Bit-rate Digital Subscriber Lines. These are DSL technologies that provision speeds above 1.544 megabits per second. There are lots of other minor variations in DSL technology out in the wild offering different bandwidth options and operating distances. These variations can be so numerous and minor, it's not really practical to try to cover them here. If you ever need to know more about a specific DSL line, you should contact the ISP that provides it for more details.
Cable-Broadband
The history of both the telephone and computer networking tells a story that started with all communications being wired. But the recent trend is moving towards more and more of this traffic becoming wireless. The history of television follows the opposite path. Originally, all television broadcasts were wireless transmissions sent out by giant television towers and received by smaller antennas in people's homes. This meant you had to be within range of one of these television towers to watch TV, just like you have to be within range of a cell phone tower to use your cellphone today.
Starting in the late 1940s in the United States, the first cable television technologies were developed. At the time, they mainly wanted to provide television access to remote towns and rural homes that were out of range of capabilities of television towers at the time.
Cable television continued to expand slowly over the decades, but in 1984, The Cable Communications Policy Act was passed. This deregulated the cable television business in the United States and caused a massive boom in growth and adoption. Other countries all over the globe soon followed. By the early 1990s, cable television infrastructure in the United States was about the size of the public telephone system. Not too long after that, cable providers started trying to figure out if they could join in on the massive spike in Internet growth that was happening at the same time.
Much like how DSL((Digital subscriber line) ) was developed, cable companies quickly realized that the coaxial cables generally used by cable television delivery into a person's home were capable of transmitting much more data than what was required for TV viewing. By using frequencies that don't interfere with television broadcast, cable-based Internet access technologies were able to deliver high speed Internet access across these same cables.
This is the technology that we refer to when we say cable broadband. One of the main differences in how cable Internet access works when compared to other broadband solutions is that cable is generally what's known as a shared bandwidth technology. With technologies like DSL or even dial up, the connection from your home or business goes directly to what's known as a Central Office(picture below) or CO.
A long time ago, the COs were actually offices staffed with telephone operators who used a switchboard(picture below) to manually connect the caller with the callee.
As technology improved, the COs became smaller pieces of automated hardware that handled these functions for the telephone companies, but the name stayed the same. Technologies that connect directly to a CO can guarantee a certain amount of bandwidth available over that connection since it's point to point. On the flip side of this, are cable Internet technologies, which employ a shared bandwidth model.
With this model in place, many users share a certain amount of bandwidth until the transmissions reach the ISP's core network. This could be anywhere from a single city block to entire subdivisions in the suburbs. It just depends on how that area was originally wired for cables. Today, most cable operators have tried to upgrade their networks to the point that end users might not always notice the shared bandwidth. But it's also still common to see cable Internet connections slow down during periods of heavy use. Like when lots of people in the same region are using their Internet connection at the same time. Cable Internet connections are usually managed by what's known as a cable modem.
This is a device that sits at the edge of a consumer's network and connects it to the cable modem termination system, or CMTS. The CMTS is what connects lots of different cable connections to an ISP's core network.
Fiber-Connections
The core of the Internet has long used fiber for its connections, both due to higher speeds and because fiber allows for transmission to travel much further without degradation of the signal. Remember that fiber connections use light for data transmission instead of electrical currents. The absolute maximum distance an electrical signal can travel across a copper cable before it degrades too much and requires a repeater is thousands of feet, but certain implementations of fiber connections can travel many, many miles before signal degrades. Producing and laying fiber is a lot more expensive than using copper cables. So for a long time it was a technology you only saw in use by ISPs within their core networks, or maybe for use within data centers. But in recent years it's become popular to use fiber to deliver data closer and closer to the end user.
FTTX
Exactly how close to the end user can vary a ton across implementations, which is why the phrase FTTX was developed. FTTX stands for fiber to the X, where the X can be one of many things. We will cover a few of these possibilities. The first term you might hear is FTTN, which means fiber to the neighborhood. This means that fiber technologies are used to deliver data to a single physical cabinet that serves a certain amount of the population. From this cabinet, twisted pair copper or coax might be used for the last length of distance.
FTTB
The next version you might come across is FTTB. This stands for fiber to the building, fiber to the business, or even fiber to the basement, since this is generally where cables to buildings physically enter. FTTB is a setup where fiber technologies are used for data delivery to an individual building. After that, twisted pair copper is typically used to actually connect those inside of the building.
FTTH
A third version you might hear is FTTH, which stands for fiber to the home. This is used in instances where fiber is actually run to each individual residence in a neighborhood or apartment building. FTTH and FTTB may both also be referred to as FTTP fiber to the premises.
ONT
Instead of a modem, the demarcation point for Fiber Technologies is known as Optical Network Terminator or ONT. In ONT, converts data from protocols, the fiber network can understand to those that more traditional twisted pair copper networks can understand.
References:
https://www.coursera.org/learn/computer-networking/lecture/Aq8AR/what-is-broadband
https://www.coursera.org/learn/computer-networking/lecture/MNim4/t-carrier-technologies
https://www.coursera.org/learn/computer-networking/lecture/kOr1o/digital-subscriber-lines
https://www.coursera.org/learn/computer-networking/lecture/riTBF/cable-broadband
https://www.coursera.org/learn/computer-networking/lecture/DG82X/fiber-connections
https://en.wikipedia.org/wiki/Point-to-Point_Protocol
https://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_Ethernet
