What Is DSL (Digital Subscriber Line)?

Today, there are multiple ways to connect your device to the Internet: cable, satellite, fiber-optic, DSL, and more. Though it's not the fastest anymore, DSL connections are the most widely used Internet access technology. In this article, we'll explain what DSL is, how it works, why it still functions for broadband connectivity, and how it's different from other forms of Internet.

What is DSL?

DSL, or digital subscriber line, is an Internet access technology that uses existing telephone lines to transmit digital data. Homes and businesses use DSL to access broadband data over the Internet.

DSL is able to carry both the Internet data and voice data simultaneously over conventional phone lines, making it a unique broadband Internet type. Broadband Internet refers to any Internet type that is always on - not just DSL, but also cable, fiber optic, and several other types.

Because data is transferred at a high frequency, you can leave your Internet connection on while making phone calls. DSL is ideal for those even in rural areas, since phone lines can be found throughout the country - even in areas where fiber and cable Internet infrastructure doesn't exist. The use of existing telephone wiring to carry data means DSL internet is widely accessible to all.

DSL has slower speeds than cable, but it’s cheaper. If all you need is to surf the web, stream movies and email your colleagues, then speed from a DSL Internet connection is fast enough to meet these needs.

How does DSL work?

A digital subscriber line uses phone wires to get you online. Note that these are the same wires that power your home phone, only in this case, they connect you to the Internet, allowing the transfer of data across the network.

To get started, you don’t need an active telephone line. All you need is the equipment: wires (Ethernet cables), a DSL modem, DSL filter (a line splitter), and a phone jack.

A graphic showing the DSL (digital subscriber line) Internet connections

Digital subscriber line equipment

Let’s start by understanding the function of each piece of  equipment:

  • DSL modem WiFi and router combo. Your ISP will provide you with a special modem that’s meant for DSL Internet. The device connects the route to a telephone line which provides DSL service. It does so through a USB port or Ethernet port.
  • DSL filter or line splitter. DSL filter separates broadband signals from regular phone voice signals. The two lines emerging from the splitter function differently. One line feeds into a DSL modem and the other one is plugged into a phone jack in your wall.
    The role is to filter the low frequency of your phone line from the high frequency of the DSL line, thus preventing interference between them.
  • Router. The router brings the Internet to your devices at your home. If you want to install a wireless network, you must have a WiFi router. Your DSL provider will also send you a router. It connects to the DSL modem via an Ethernet cable.
  • Ethernet cable (wires). The DSL modem uses Ethernet cables to connect to your router.
  • A phone jack or wiring. A digital subscriber line connection requires wiring for landline phones in your home. A DSL modem is plugged directly into a phone jack in the house after the DSL is installed.

As mentioned, a digital subscriber line works by using common telephone lines which are nearly everywhere. These standard copper wires run from your house out to a box and eventually connect to the larger telephone network. Most households have these wires already installed.

Signals are sent from the ISP via the telephone lines to the DSL modem. The modem then translates and converts them digitally into what you need to get online. Data is routed to you wirelessly or through an Ethernet cable.

Features of digital subscriber lines

There are several key features of digital subscriber lines that set it apart from other methods of connection. First and foremost, DLS uses existing phone lines to transmit high-bandwidth data. Because so many people have foregone landline phone services, DSL attracts a great deal of interest from Internet service providers, leading to the increased popularity of DSL service in urban and underserved areas.

With DSL, Internet use and phone calls can happen concurrently, which isn't completely unique but does set it apart from other methods that use phone lines like dial-up. This makes DSL a good choice for organizations and homes that need to perform both tasks at once.

Finally, digital subscriber lines and voice calls coexist on the same copper lines. Think of band as a lane in the freeway; Internet signals go through copper wires at a much higher band while phone signals occupy a much lower band. Therefore, each service utilizes its own frequency band and the copper lines can handle both at once. Furthermore, in most cases, DSL connections are asymmetric, with faster download speeds than upload speeds.

This is aimed at optimizing user experience because most of us engage more in downloading than uploading. Even better, a line splitter is commonly installed on phone lines to keep the voice band clear of any noise. The small DSL filter also blocks high frequencies.

Types of DSL

There are several types of digital subscriber lines. Below, we'll differentiate between them and explain each type.

Asymmetric DSL (ADSL)

Asymmetric digital subscriber lines give you faster download speeds, which is data coming from the Internet to your device, than upload speeds, which is data going from the user back to the Internet. Most homes are connected to ADSL because Internet users typically download more than they upload.

The speed of ADSL internet depends on where you live, as it varies by the distance between where you are and the central office of the service provider. Therefore, ADSL is a distance-sensitive technology.

As the connection length decreases, signal quality increases. It means ADSL users nearer the central office enjoy extremely high speeds. They have faster connections far above the promised maximums.

On an average, ADSL technology offers download speeds anywhere between 5 Mbps to 100 Mbps. This is fine for everyday Internet activities like checking or tracing emails and browsing online.

Symmetric DSL (SDSL)

The working mechanism of symmetric DSL is completely different from that of asymmetric DSL technology. For symmetric digital subscriber lines, download and upload speeds are the same. Symmetric DSL splits the upstream and downstream frequencies evenly.

SDSL is sometimes referred to as single-line digital subscriber line because it delivers data connection over a single pair of copper wires. This type also uses the entire bandwidth and operates at a range of 3000 meters, or approximately 10,000 feet.

Furthermore, SDSL transmits data at speeds of up to 3Mbps. But this is only with a high-quality telephone circuit and when the length of the local loop connection doesn’t exceed the maximum range of 3000 meters.

SDSL is mainly intended for small and midsize businesses that require stable connections but aren’t ready to invest in a leased line.

Very high-bit-rate DSL (VDSL and VDSL2)

This technology is considered the fastest form of DSL. VDSL is a more reliable connection than others. It promises up to 100 Mbps bandwidth for upstream and downstream speeds over short distances. The shorter the distance, the higher the speed.

VDSL works over a twisted pair of copper wires to boost faster data movement. The Internet connection service can handle data for high-definition television (HDTV) and can also move data for telephone lines. Your provider can help configure VDSL to operate symmetrically or asymmetrically. This will, however, depend on the application.

There is also VDSL's successor, VDSL2, which offers even faster speeds. With a capacity of around 100 Mbps, the technology is used with Triple Play offerings (voice, data, and video) across longer distances.

High-bit-rate DSL or HDSL

This type uses two sets of 24 AWG standard copper wires to offer upstream speeds of 12 Mbps and downstream speed of 52 Mbps. HDSL2 and HDSL4 are its predecessors.

Single-pair, high-speed DSL or SHDSL

This type provides faster Internet connectivity over copper cables. It’s ideal for businesses that use web hosting, secure connections and PBXs because it supports asymmetric data rates. It also benefits corporate LAN applications.

Advantages and disadvantages of DSL


Using a digital subscriber line connection has several advantages over other types of wired Internet access.

  • Affordability – Thanks to the existing telephone lines that support the connection, DSL is one of the cheapest Internet options available.
  • High-speed file downloads – The technology performs better over traditional dial-up methods, with optimum downloads that are far greater. DSL has only improved over time to meet high-speed demands.
  • Availability – DSL is significantly more available than other Internet services because it runs over telephone lines that are nearly everywhere. The wires have plenty of room to handle a range of frequencies, and DSL takes advantage of this extra capacity to carry its data.
  • No bandwidth sharing – With digital subscriber lines, you don’t have to share bandwidth with your neighborhood like with a cable connection. Everyone using DSL has their own dedicated connection. You’ll experience less downtime as a result.
  • Greater reliability – Speed reliability is a concern with Internet connections. DSL services are reliable because the connection is specific to your telephone line. Because of this, peak traffic hours don't affect your connection.
  • Availability of DSL modems by ISPs – Your Internet service provider can send you a modem - a gateway - that connects to multiple PCs and mobile devices


Before investing in a DSL service, you should consider the following downsides;

  • Speed issues. Digital subscriber line isn’t as fast as cable or fiber. Data speeds over telephone lines vary depending on the distance from your home to the hub. VDSL technology, for example, is consistently fast, but only for short distances.
  • Not ideal for big businesses. Homes and small business operate with DSL Internet best. Home users download more data they upload. Small businesses prefer digital subscriber lines for activities like sending data.

Large businesses should be mindful of the shortcomings of DSL depending on their goals.  Many of them send large amounts of data, files, and programs between networked offices so they may want to opt for fiber or cable Internet.

Comparing digital subscriber lines to other Internet connections

Digital subscriber line connections have been around for years, but their speeds can't match what fiber-optic and cable Internet offer. However, it's still a solid choice, especially compared to slower connections like dial-up.

DSL vs fiber optic

Fiber optic connections provide the best speeds available because they use light to transmit data via fiber optic cables. Fiber optic Internet offers download and upload speeds of 1000 Mbps, which isn't even comparable to other Internet connections today. For reference, VDSL2 caps at around 100 Mbps.

In many areas, fiber-optic cable service is replacing telephone lines. This makes fiber-optic Internet more readily available. However, digital subscriber lines are still the more available option; fiber-optic is also more expensive, meaning it might not be the best option for those on a budget.

DSL vs cable

Cable Internet is a form of broadband connection delivered over coaxial cables, which are the same cables that deliver your cable TV services. With cable, users get significantly faster Internet than what DSL offers. Cable download speeds reach up to 1Gbps, which makes it ideal for residential users.

However, because cable Internet uses a shared network, Internet speeds may vary depending on when your neighbors use the Internet. With DSL, peak use times don't affect individual user speed.

DSL vs dial-up

Digital subscriber lines most closely resemble dial-up connections. Both use phone lines to carry data. However, digital subscriber line Internet is much faster than its predecessor and allows you to use the Internet and make phone calls at the same time, something that dial-up Internet cannot do.

How fast is digital subscriber line?

Actual speeds of digital subscriber line services vary. It all depends on certain factors, including your provider, location, and what package plan you pay for.

There are different forms of digital subscriber line connections to choose from. You can go for asymmetrical DSL if you require much higher bandwidth for downloading data. The majority of users choose asymmetric digital subscriber lines because they do more downloading than uploading.

Symmetrical DSL is another option where both upload and download speeds match. VDSL2 is another speedy connection but for short distances.

ISPs are likely to offer tiers of connection speeds ranging from lower to higher. You can check your own service with a DSL speed test. The following factors impact high-speed DSL rates:

  • Distance between your home and service central office – The farther you are from the hub, the slower your connection will be. Consider this when subscribing to your service.
  • Phone line quality – Having quality phone lines means great connection speeds. Areas with high-grade copper wires receive favorable digital subscriber line speeds.
  • Technical difficulties – Like any service, digital subscriber line services experience technical problems that users can't fix.

Ethernet connections can help if you have bandwidth-intensive devices like gaming computers. An up-to-date modem is also essential when it comes to boosting your Internet connection speeds.

Frequently asked questions

What does DSL mean?

DSL stands for digital subscriber line.

Is digital subscriber line Internet reliable?

Digital subscriber line Internet is mostly reliable, as it uses pre-established connections via phone lines in your neighborhood or area.

Should I get DSL Internet?

It depends on where you live. If digital subscriber line is the only Internet connection available, or if you live in a rural area, then consider it. However, if you live in an area with many Internet options, you may want to choose fiber-optic or cable Internet instead.

Is DSL the same as WiFi?

No, DSL is not the same as WiFi. DSL provides access to the Internet, which WiFi cannot do directly.

What does digital subscriber line Internet cost?

Prices range between DSL Internet providers; however, on average, it costs $50 a month.