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How DSL Works

electronics.howstuffworks.com — When you connect to the Internet, you might connect through a regular modem, through a local-area network connection in your office, through a cable modem or through a digital subscriber line (DSL) connection. DSL is a very high-speed connection that uses the same wires as a regular telephone line.

Who dugg this? Made popular Oct 8, 2007

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  • mrjit, on 10/24/2007, -1/+65What are we going to throw random howstuffworks.com articles up for newbs nowadays? Should I do a How BGP works, How OSPF works, How Digg works too?
  • fridx, on 10/10/2007, -1/+35ADSL = Asymmetrical Digital Subscriber Line (i.e. your downstream is greater than your upstream) SDSL = Symmetrical Digital Subscriber Line (i.e. same up and down stream) There are various and lesser known others, but DSL basically just means broadband, but not cable.
  • tradwolley, on 10/10/2007, -0/+23Great article and all, but do we really need these articles from HowStuffWorks on the front page?
  • OutThisLife, on 10/18/2007, -0/+18Have you seen the HILARIOUS dancing baby?
  • dagamer34, on 10/18/2007, -2/+14DSL's Advantages: Connection not affected by others in your area, more likely to reach speed cap, usually costs less.
    DSL's Disadvantages: Requires specific distance from branch exchange, higher pings compared to cable, slower speeds, worse for gaming

    Cable's Advantages: Faster speeds, lower pings, wider availability, generally better for gaming
    Cable's Disadvantages: Shared neighborhood connection, rated speed not to be believed, usually costs more.

    FiOS Advantages: Best speeds, amazing upload speeds (2Mbps+), Did I mention the speeds? (30Mbps down!), cheap compared to dsl/cable.
    FiOS Disadvantages: Restricted to select areas in the states or Japan, Verizon converts you away from POTS (which means your phone line will always be stuck with them unless you pay your new phone company to replace installation).

    Internet connections in a nutshell.


  • STARTSOMETHING, on 10/10/2007, -1/+11I thought everyone knew about How stuff works.com
  • minorthreat, on 10/10/2007, -1/+10digg me down, but hi... welcome to the year 2000 :)
  • fridx, on 10/10/2007, -0/+7Not really, you are pretty much guarantied to get a 2Mb/s connection (at least in the UK anyway), but its when ISPs start offering "Up to 8Mb/s" (And in some cities "Up to 24Mb/s"), that the distance starts to affect your speed. I'm over 2 miles away from my telephone exchange, and I get a 4-5MB/s connection (depending on current network usage). And now, ADSL is available virtually everywhere, I don't know of a town that doesn't have an ADSL enabled exchange, and only a few villages and rural areas are still unable to receive ADSL, so the disadvantages listed are pretty much irrelevant.
  • eviscero, on 10/18/2007, -0/+7I pay 49 bucks a month for 20mb FIOS

    Dsl via Verizon opens at $49 for what? 768kps?

    laughable - I buried this because unless you're still on 56k - who gives a shat about this sluggish and outdated tech?
  • pfeester, on 10/10/2007, -0/+7buried...lame.
  • manitoba98xp, on 10/18/2007, -2/+9Damn Small Linux :P
  • inactive, on 10/10/2007, -0/+3You can usually get a naked line from your DSL provider, and then you pay for ISP service on top of that, so if you use VOIP or some other phone service, that's fine. There's no requirement of DSL that says you must purchase phone service from your SL provider.
  • vanscott, on 10/18/2007, -2/+6Have you read any of the conversations here about bandwidth? They all basically go like this, "gimme more bandwidth already" and "but Korea....". While I would love more bandwidth, I know what the current limitations are and the cost and effort needed to deploy next generation access networks.

    I think it is great to see articles dugg explaining networking and telcom infrastructure.
  • CaptainHarlock, on 10/10/2007, -0/+3Trick question. DSL doesn't work.
  • Cerebral, on 10/10/2007, -0/+3Yes but you have failed to understand that we've already given the telcos money (tax payers that is) to give us the "promised faster speeds" however they have not delivered yet. It is they who have failed the internet.
  • majordannyboy, on 10/10/2007, -2/+5Most of the time when you hear DSL they are meaning ADSL. SDSL isn't sold much unless you ask for it specifically and you have to install a second set of wires, meaning that you cannot have SDSL and speak on the same pair of wire. Just like fridx said, SDSL is the same speed for both UPLOADS and DOWNLOADS, so if they say you have 1 Mbit/s that means 1 Mbit/s UP and DOWN. On an ADSL circuit you can have different speeds for UP and DOWN, mostly it is higher for DOWN then UP.
  • uaudio, on 10/10/2007, -1/+4buried. DSL works because of magic leprechauns, everyone knows that.
  • ChildeRoland420, on 10/18/2007, -0/+2AT&T does NOT require a phone line to have DSL (in most areas). In fact there was recently an article on Digg about it. I signed up for service but am still waiting to be activated.
  • Lennalf, on 10/10/2007, -0/+3you probably meant e.g., not i.e.
  • reuscel, on 10/10/2007, -0/+3We know how it works. It's a series of tubes.
  • Yildrak, on 10/10/2007, -0/+3False. DSL connections ARE affected by other users in the area, as they're on the same (telephone) cable distribution box in the street. If anything happens to that box, all the lines are affected. Similarly, a technician fixing one line in the neighborhood could have an effect on yours. Where you ARE correct, is that DSL doesn't work with circuit loops like cable does. You're also false as far as the pings are concerned, that's only true with an interleaving (error-correcting) profile on the line. It would depend on the ISP of course, but most ADSL providers in Belgium have a ping of 25 ms, more than low enough to even play an FPS with online. And as to reaching maximum speed: unless your line has too much signal loss or unless your modem/router has locked up, your speed always equals the synchronisation speed.

    As to cable: the MAXIMUM speed is higher. The practical speed in cities will almost always be just double that of a regular ADSL line, and the same as an ADSL 2+ line, given the varying nature of speed on a cable line.

    As to what people have said about having to pay phone costs... you could always as for a line WOV (without voice), to receive only the DSL signal without the phone options enabled.
  • tendonut, on 10/10/2007, -0/+2I am so disappointed with how HowStuffWorks has gone down the toilet. I remember back in the day when this article was new and when they did articles like "How RAM Works". Now it is just total *****, things like "How Hummers Work" where they basically put up a commercial for Hummers, or "How Paris Hilton Works", things that just have no place in an educational site. I remember about a year ago, they were bold enough to put up an article called "How Media Center PCs Work" which was basically a big 4 page commercial for Windows MCE with absolutely no useful information whatsoever.
  • tendonut, on 10/10/2007, -0/+2DSL here in WNY has 3 times the upload of cable if you are lucky enough to be close to the station. I normally am at around 2.8MBps/700KBps on a 3MB/768KB line. Cable here is 4MBps/256KBps and me being a dedicated host for all our online games, it really makes a difference.
  • random12345, on 11/16/2008, -0/+2dugg for spite
  • Matteos, on 10/10/2007, -0/+2That's because they are wet!
  • tedjar, on 10/10/2007, -1/+3OK well apparently we DO need articles from HowStuffWorks since none knows even the difference between ADSL and DSL. Asymmetric Digital Subscriber line is what most users get, where the download speed is greater than the upload. The A just gets left off since almost no one but commercial users use anything but. SDSL (Symmetric Digital Subscriber Line) has equal upload and download speeds.
  • mrmacky, on 10/10/2007, -0/+2Because I love that high-quality AT&T voice and data plan... wait
  • mrogi, on 10/10/2007, -0/+2The only thing DSL ever did for me is make me appreciate my cable modem connection.
  • rcollamore, on 10/10/2007, -2/+4i like girls with DSL
  • joshuaer, on 10/10/2007, -0/+2In the USA Well at least in Minnesota moist Phone lines out side of Major cities are split and DLS will not work on them or if it does it can only move at about 786KBs
  • brotherfranciz, on 10/18/2007, -0/+2You probably meant tubes, not tunnel.
  • pnmoore, on 10/10/2007, -2/+4The problem is the US is such a large country, and still has so many rural areas, that a lot of the population just can't be served effectively (or affordably) by DSL.
    Also, believe it or not, even in cities a lot of people are not as close to the equipment serving their DSL service as you are (~2 miles), and it is the length of the wire that matters which doesn't always jive with distance to the central office. For example, if you are 1 mile from the central office the copper plant (wire) may follow certain roadways to supply service to the greatest number of people that results in the wire being much more than 1 mile in length. Some of the newer technologies are able to overcome distance some, but not totally.
    Additionally, some of the older copper in the ground has issues due to age that shorten the usable distance.
  • funkytaco, on 10/10/2007, -1/+3Yes, ADSL is just DSL with a smaller upload. Businesses usually need to upload as much as they download ( i.e. backups, websites, VOIP) so they usually get SDSL which is symmetrical ("the same") up and down in download speed. Keep in mind the bandwidth up and down is shared (like traffic going through a tunnel).
  • NullzipZero, on 10/10/2007, -0/+2I agree.
  • funkytaco, on 10/10/2007, -0/+2I used to work Tier 2 DSL for Mindspring (I quit before Earthlink outsourced to whoever; Phillipines, India, etc). Note that CAP is not used any more. DMT is the standard.

    Note that I had tools to check signal strength of your phone line and the most common interference I ran across in over 2 years of non-stop phone calls 8 hours a day was devices inside the house (phones, satellite on phone line, dsl bridge sitting on radio devices, etc). Always filter devices on your phone line as they keep the devices working only inside of their spectrum, as mentioned in the article.
  • timdgibson, on 10/18/2007, -0/+1Yes you can get a naked DSL line, but at least in the Chi-town area, AT&T prices it so it doesn't make sense financially. We have the most basic phone line (basically a dial tone) and then the DSL service on top of that. It comes to the same amount as the naked DSL line.
  • sammcj2000, on 10/10/2007, -0/+1buried for too boring for a front page story
  • subxero37, on 10/10/2007, -0/+1Most phone company-based DSL providers (AT&T, namely) make it a requirement. But since most people are under AT&T's telecom monopoly, I guess it really doesn't matter.
  • amitgawande, on 10/10/2007, -0/+1Totally in agreement. What's the point if whole internet gets digged!!!
  • TRENT310, on 10/10/2007, -0/+1Same, my telephone company sent me a "free trial" modem one day and I tried it for 5 minutes before sending it back the next day. They still charged 1 month service, though.

    People who complain about unstable speeds...get a business plan and complain to your ISP. I complained and now I'm on a seperate router.
  • doubleblack, on 10/10/2007, -0/+1Why? To teach people like you what DSL is.

    BGP and OSPF are protocols, while DSL is a technology...
  • inactive, on 10/10/2007, -0/+1This is good for the noobs.
  • etx313, on 10/10/2007, -0/+1I know how they work, I just don't know where they come from. ba-da-ching.
  • Guspaz, on 10/10/2007, -0/+1My parents' DSL line in Montreal has a first-hop latency of 6ms; her PPPoE session terminates in Montreal. My DSL line, on the other hand, terminates in Toronto, so my first hop latency is about 16ms. That's what the extra 600 KM adds.

    DSL connections are not affected by other users in the same area. The first possible bottleneck is at the CO, and the usage patterns of other users will only affect your speeds if the CO's connection to your ISP's network is saturated.

    In practice, this doesn't happen often, and when it does, it's considered a network problem that needs fixing. ISPs that use Bell Canada's copper, DSLAMs, and ATM network, pay for and expect full speed services. In the end, it usually comes down to saturation on your ISP's upstream connections. At that point, you're far past the last mile where DSL is involved.

    I'd also say that the practical speed for cable isn't much higher than DSL if you take ADSL2+ into account (which you only seem to do in part). A standard DSL line in Montreal is 7mbit. A standard Cable line in Montreal is 7mbit. It's only when you get to the higher tier that the cableco offers service at 20mbit and Bell only offers DSL service at up to 16mbit. While the technology supports up to 24mbit, you have to be pretty darned close to the CO to sync at those speeds; 16mbit with DSL is a much safer bet, but still by no means guaranteed.

    It's also worth noting that dry loops (what you call WOV) tend to have extra fees. In Canada, while the telcos are required to offer dryloop services to other ISPs, they're allowed to charge dry loop fees that start at $7.25 per month, and increase depending on distance.

    That said, I chose DSL because there's choice there. There isn't really any choice with cable ISPs, except a handful that resell the local cableco and are still subject to the same usage caps that the cableco sets for their own customers.
  • bloaded, on 10/10/2007, -0/+1it shows
  • blubberlump, on 10/18/2007, -2/+3If by "very high speed connection" you mean "pathetically slow connection compared to competing technologies that are often cheaper."
  • Matteos, on 10/10/2007, -0/+1Fail!
  • Onyxblaze, on 10/10/2007, -0/+1Woot. Go Latin!

    >>you probably meant e.g., not i.e.
  • knomevol, on 10/10/2007, -0/+1asynchronous indicates that the download speed versus upload speed is not equivalent, always in favor of download speed to a residence. businesses and geeks may prefeer synchronous pipes whereby they may upload their trash to the world as fast as they can download it.
  • inactive, on 10/10/2007, -1/+2You can definitely use your phone simultaneously line with an SDSL connection. I did it for years with NewEdge. Not sure what they're on about.
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