What is a Digital Subscriber Line?

Mary McMahon
Mary McMahon

A digital subscriber line (DSL) is a technology which allows people to transmit digital data along with voice along a phone line. There are a number of different technologies under the umbrella of DSL service, with the most common being an asymmetric digital subscriber line (ADSL). In fact, many people use the term “DSL” when they are actually referring to an ADSL, illustrating how widespread this particular form of the technology is. Many people around the world use this technology to access the Internet, both at home and in office environments.

A DSL filter.
A DSL filter.

This technology allows people access to high speed Internet using existing wiring. Competitors such as cable and satellite Internet services may require adding wiring, depending on whether or not a structure has been fitted with the necessary wiring. It is also important to note that digital subscriber line services are not available in all areas because the technology is distance sensitive; people too far away from a hub will receive a signal which is too weak to use. Many companies which provide this service are increasing the number of hubs to increase their broadband penetration and attract more customers.

An ADSL modem.
An ADSL modem.

Phone lines are capable of transmitting much more data than just voice. A relatively small low-frequency range is reserved for voice transmissions, leaving room for other data in the line. A digital subscriber line uses the high frequency areas to send and receive data, breaking a phone line into a stream for voice, a stream for downloading, and a stream for uploading.

With ADSL, more bandwidth is reserved for downloading, which is why people may have noticed that it tends to take less time to download data than it does to upload it. Symmetrical digital subscriber line technology, on the other hand, reserves equal amounts of bandwidth for both uploads and downloads. Most people find ADSL perfectly suitable for their needs.

To transmit both voice and digital data, a digital subscriber line needs a filter. Filters are fitted on the phone line to split the data streams; people can plug a DSL modem into the digital data side of the splitter and a phone line into the voice data side. Modems can also be used for home networking, and may be wireless to allow people to access the Internet without needing to be directly plugged in to the modem. However, transmission speeds can be faster when wired directly into the modem.

Many people around the world use this technology to access the Internet, both at home and in office environments.
Many people around the world use this technology to access the Internet, both at home and in office environments.
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a EasyTechJunkie researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


We recently bundled our TV, internet and telephone with the same company (Charter). When the technician disconnected our telephone line from our former provider and hooked the phone through the cable digital service, he installed a large DSL filter over our wall phone jack plate. We just purchased new telephones and the wall base is so ugly. It came with an adapter wall plate and sits up high on the wall.

We are wondering if we still need the wall jack, since we have wireless service or if we need a wall jack if we can just go to an in-line dsl filter. It's not an analog phone, it has DECT 6.0 technology. Can you help?


At my office, we use a very high speed digital subscriber line. I work at a newspaper, and we rely heavily on the internet.

We receive hundreds of emails every day. Some contain information from advertisers, like credit card numbers for payment or content for their ads. Some freelance writers email their articles to us for printing. Also, we update our website several times a day. We can’t afford to have slow or unreliable internet.

I remember a few years ago when we had satellite internet. It seemed to always go out on the days we were the busiest, and it would delay the printing of the paper, because we were missing vital information for the issue. The boss decided that we needed to avoid this, so we got DSL.


We used to have dial-up internet. We got DSL after my sister became a teenager and started needing the phone all the time, though.

With dial-up, she had to wait for my dad to get off the internet before she could call anyone. She was always complaining that she might miss an important call because he was online.

He got tired of being interrupted by her whining all the time, so we got DSL. I’m glad we did, because it is much faster. It used to take me about ten minutes to check my email, and now, I can do it in seconds.


DSL is unavailable where I live. It will probably be years before people around here can get it. So, we have satellite internet.

It has many drawbacks. Whenever a thick cloud cover moves in, the internet goes out. So, every time it a thunderstorm rolls in, I can’t check for weather warnings using the internet.

Also, satellite internet tends to be slower than DSL, which I use at work. There, I can click through multiple frames within seconds. At home, it takes as long as five minutes for a single page to load at times.

I really wish it were available in my hometown. I guess all I can do is wait and hope, though.


@SailorJerry - All other things being equal, cable internet is usually faster. However, in a lot of places DSL is more reliable - fewer of those irritating mini- (and not so mini) outages.

Another consideration is that because DSL comes from the phone company over your existing phone line, you generally have to have a home telephone (landline) in order for DSL to be an option.

I had DSL a couple years ago, and it was quite reliable. At our next place, we had good cable Internet, which we really noticed being faster. But now, we have a different cable provider. Not only is it not as fast (you never really get the speed they advertise), it's not very reliable. I wouldn't mind going back to our old rock-solid DSL, but we no longer have a landline.

Getting home phone service *and* DSL would just make it too expensive for us.


How does DSL internet compare to cable? They are both available at my new house and I not sure which one to get. I don't have a service history with either provider.

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