Networking 101: The DSL Modem DSL stands for digital subscriber line. While it may not be the broadband choice that most would choose over fiber or even cable to receive internet, the reality is that in the 2013 US Census data, 21% of Americans were using DSL for their internet connection. Therefore, while it may not be the latest and greatest way to get your internet, it is not going to disappear anytime soon. The DSL modem is the device that connects the home router to the phone line for the connection to the internet.

Recall that DSL is based on transmitting the data over the old fashioned copper phone lines. While voice over copper (POTS- plain old telephone service) gets sent on the 3.4 KHz frequency, the data gets sent on a higher frequency of 8 KHz, allowing both voice and data to be transmitted simultaneously. The DSL modem has both an RJ11 jack to connect to the phone line, and an RJ45 jack to connect to the Ethernet cables. The phone line in turn connects the subscriber line to the switching center. The data connection is always on and active, and at the local switching center the data is sent to the internet connection, and does not enter the telephone network. The local switching center then has a DSLAM (digital subscriber line access multiplexer) that has a direct connection to the internet. Here in the US, DSL usually refers to ADSL, with the “A” standing for asymmetric. Originally modems were developed to send the data over the telephone line on an audible frequency, like a fax machine. ADSL was an improvement on this, which sent the data on a separate frequency than the voice communication got sent on. The advantages included faster speeds, and simultaneous voice and data communication. DSL requires microfilters on the phone lines to keep the data signal from causing interference by blocking any frequency above 4 KHz. The maximum download speed for ADSL is 8 Mbps, with an upload maximum speed of 640 Kbps. A limitation of ADSL is that the end user must be within 18,000 feet away from the source. Only at the closer distances will the speeds achieve close the theoretical maximums, which is why ADSL gets referred to as a distance-sensitive technology. Further out, as the signal degrades over the copper line, the signals significantly degrade, and the speeds slow down. For example, while the maximum distance is 18,000 feet, once a user is beyond 6,000 feet, the speed will be less than the maximum. In the ADSL protocol, the modem and the DSLAM communicate over the copper line via DMT (discrete multitone modulation). This takes place on the 8 KHz frequency, which segregates the data on a higher frequency from the voice communication. This then got revised to ADSL2 which increased the download speed to 12 Mbps, and the upload speed to 1 Mbps. The further revision was to ADSL2+, which pushed the download speed to an almost broadband speed of 24 Mbps (FCC download speed for broadband is 25 Mbps), and an upload of 3 Mbps (which not coincidentally meets the FCC minimum for broadband upload throughput). Realize that these download speeds are maximum speeds, and DSL is highly dependent on the distance away, and speed drops the further away, to the point that many users never see the maximum speeds. With the above speeds, it is no mystery why users flock away from DSL when fiber and cable internet alternative exist. In some cases, DSL connections got replaced with these newer technologies (on a personal note, that is what happened in my neighborhood when Verizon’s DSL got replaced with Fios). However, this kind of transition to newer technologies has not happened for all users, and the G.fast broadband standard is designed to address these limitation. This technology is using even higher frequencies on copper lines to reach speeds of 1 Gbps over existing telephone lines; however the distances are limited to 400 m. There is also talk of an even faster standard, XG.fast, which could bring 10 Gbps speeds at close distances. However, in the interim, G.fast has not seen widespread deployment, although CenturyLink recently deployed G.fast to 800 apartments in Wisonsin, so the potential is there. While ADSL may not have the pizzazz of fiber, it soldiers on and provides internet access for a substantial portion of the US. With additional protocols, it still can increase speeds, and remain competitive with cable and fiber offerings. Feel free to discuss your ADSL experiences, especially for users that could get their internet from another source, but remain on ADSL by choice. This article was contributed by the DSLReports.com community. If you'd like to receive payment for writing content like this for our front page, please drop us a line.







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Most recommended from 49 comments



Darknessfall

Premium Member

join:2012-08-17 Cisco DPC3008

Asus RT-N66

5 recommendations Darknessfall Premium Member VDSL2



Below are my VDSL2 stats -



I might have missed it, but I don't see VDSL2 mentioned in this article. VDSL2 was a pretty big upgrade from ADSL2+ for those close enough.Below are my VDSL2 stats -

WHT

join:2010-03-26

Rosston, TX 4 recommendations WHT Member Distance Limits When we rolled out DSL in PacBell in '98 or so, the limit was 18,000 feet (Verizon when it was still GTE used 18,500) for 1.5 Mbps.



As faster speeds evolved, it was realized 18,000 feet was too far. I forget the new install qualifications but I think it was 10,000 feet for 5Mbps and less than 5,000 for 10 Mbps (same for CenturyLink's 20 Mbps Prism as it was two pair bonded).



Telcos started enforcing Limits for new installs around 2005. An AT&T tech told story of an account disconnected for non-payment at 15,000 feet that worked fine was not able by policy to re-establish new service at all.



To their credit CenturyLink started dropping remote DSLAMs all over the county. Of course that couldn't be said about Verizon and AT&T.



As for the too often repeated "aging copper lines"... copper doesn't rot though roadside pedestals get damaged and most outside plant by 80s was upgraded. On other hand there are still places in Verizon's Dallas area still on paper pulp aerial cable in 2015! Freaked me out in late 80s when I was opening splice boxes on the pole back then, but still thirty year later? SMH ramsaso

Premium Member

join:2014-01-04

Houston, TX ARRIS SB6183

3 recommendations ramsaso Premium Member DSL. I pay for 6Mbps ADSL through DSL Extreme and I can tell you that it's more than enough for what I utilize on a day-to-day basis and it's capable of streaming HD content (720p) so it's not a big deal really. Additionally, it's cheaper than what CumCast Comcast charges for 10Mbps (even with that speed improvement).



Also, DSL is my only connection to the internet since we cannot get U-Verse/TrueStream here at all and Comcast can't serve us because of a shitty contract/deal my apartment complex has with a cable company that's been fined by the FCC (I would like it should Comcast decide to service this area even with the 1TB data cap that's put in place).

CCarson

join:2001-07-22

Redlands, CA 236.8 10.5

2 recommendations CCarson Member Why I stick with DSL... Though I have the option of cable (Spectrum) or FiOS, I stick with 3MB DSL. Why?

* I'm a one-person household; don't need lots of bandwidth for just one person.

* I don't watch lots of video over the internet: I use an antenna and HTPC/DVR, plus disc rentals from our local rental shop (yes, we have one!) or the library (or just read a book).

* So the copper in our neighborhood is old and the DSL goes out for a few hours when it rains heavily; the DSL is less than half the cost of the lowest cable tier, even at the introductory price (not considering all the taxes and fees Spectrum heaps on top of the base price).



I'd jump ship immediately if there were a cable or fiber option available at a low cost, but that just doesn't seem to be in the cards.

Duramax08

To The Moon

Premium Member

join:2008-08-03

San Antonio, TX 2 recommendations Duramax08 Premium Member Ever since 2004 I was calling AT&T to see if we would ever get DSL and they told us no, but that they are working hard to expand to our area. Now its 2016 and we still get nothing. Up a mile down the road they dropped fiber and network equipment for a new massive warehouse so I thought I would give them a call and see if anything changed. They were able to send me to the research department and they did some looking around and told me they have no plans of servicing my area for either DSL or uverse, period. I would go for cable but they end 2 miles away. Atleast I got a somewhat decent WISP that does 7/1 for $50 a month.