DSl and dial up both go over the phone lines don’t they? Is broadband even faster?
I think, though I am not certain, that DSL achieves higher bandwidth than a regular modem through using a broader range of frequencies (in fact, this was the original meaning of “bandwidth”: The width of the band of spectrum that you’re using). Broadband is a more general term, referring to any sort of internet connection faster than a 56k modem. DSL and cable are the two most common forms of residential broadband, but in an institutional setting, there are other options. Well, OK, those other options could be used residentially, too, but they wouldn’t be cost-effective.
Mmm, DSL is broadband…
DSL is broadband with cable being the other fast home solution. Broadband just refers to the fast connections available for home and maybe small business use. Big businesses have lines that are just as fast but they are a little different. The faster alternative depends on where you are. Cable tends to be faster in most places often being close to 100x the speed of dial up DSL is usually about 20x faster but this isn’t always true. There are some very fast DSL packages available in places and some test cities that have DSL that is several times as fast as most cable solutions.
Both alternatives are doing well and increasing speed the same way computers themselves do. DSL works through a band on the phones lines that don’t carry voice. You can use both DSL and the regular phone at the same time because of this. The problem with DSL is that it is best suited to high population density environments because the signal can only travel so far from some of the telephone company equipment.
It’s carried on frequencies above the upper frequency cutoff for POTS (Plain Old Telephone Service), and it is a broader range of frequencies. The high frequency signals attenuate rather quickly when transmitted over twisted pair, too. Hence the distance limitations of DSL.
Some background:
The primary difference between DSL and cable is that–technically, at least–if you use a cable modem, your connection can conceivably be reduced in speed if many people in your neighborhood are using the same service. In a way, you are all “sharing” the same lines.
But DSL relies completely on your phone line, so it shouldn’t interfere with your internet connection; however, if your phone company goes down, (which is quite rare in the US), then you won’t have internet serivice.
First, the term “modem” (MODulator/DEmodulator) is/was properly applied to a device that translates digital signals into analog signals and vice versa. It has been generalized into a term for any device used to establish a connection to the Internet. In reality, a DSL or cable “modem” is a bridge, it connects two different physical network types. The connection from your home network into the DSL or cable network is all digital.
“Broadband” is also a term that has been (mis)adopted. Originally, it meant a network design where two or more separate signals are transmitted over the same physical connection, using different frequencies (The opposite, one signal on a wire, is called “baseband”). DSL and cable Internet are both broadband technologies according to the original definition, since your phone and DSL operate on the same wire, as do cable TV and cable Internet.
If we put this all together, we see that DSL is not some type of enhanced dial up, even though it uses a phone line. It works with a separate digital protocol that is transmitted alongside voice communications. The reason it can be faster than an analog connection is digital signal encoding is more efficient than analog encoding, allowing more data to be transmitted in a particular frequency range.
There is a dedicated (connects only to your house) phoneline between you and the phone exchange, in so far dail-up and DSL use the same line. the difference is what happens in the phone exchange. When you use dial-up the phone exchange connects you through the phone-system designed for voice, this is a very limited system (maximum bandwith 56K).
The factor limiting your bandwith here is not the copper between you and the phone exchange but what happens IN the phone exchange.
DSL puts a signal through that same copper wire using two dsl-modems, one at your end and one in the phone-exchange. There your signal gets put through a glass-fiber or other high-capacity connection, by-passing the limitations of the phone-exchange.
Yes, the closer you are to the telephone substation the better.
Esri.com and Dslreports.com provide distances to substations.
Isn’t the same thing true of DSL?
That’s what the Contention Ratio represents me thinks
Once your individual signal reaches the local exchange you share the same connection from there to the ‘internet’ (I think it’s called a SLAM? Or DSLAM?)
Yes. Typically a home DSL user contends at 50:1. This keeps costs down, but it makes for some very noticeable contention issues around here. My home connection struggles for an hour or two after the schools come out as the brats all log onto their “Myface” and “Gootube” malarkey. Why in my day it was all fields around here…
Of course I could pay for a T1 line or something for a guaranteed d/l speed, but those are expensive.
Sorry, but no. Broadband has always meant “using a wide range of frequencies” and refers to the bandwidth of a single signal path. The number of “signals” (I put this word in quotes because it’s really just one signal being sent down a given pathway, even though there are multiple separate information “streams”) is irrelevant; it’s the amount of information being transmitted per unit of time which matters here. Transmitting a large number of individual “signals” requires more bandwidth than transmitting a small number; likewise, transmitting a given amount of information in a short amount of time takes more bandwidth than transmitting the same amount of information over a longer time period. The term for putting multiple signals through a single path is multiplexing, which is what you were referring to.
Any fast data transmission method is broadband, compared to a slower method, by definition. Even if it’s just one signal.
Both DSL modems and cable modems are properly called modems. In both cases, digital signals are modulated onto analog carriers to transport them over the communications link. They do not use baseband signaling.
Cable: Offered by cable TV companies. Shares services in one trunk line; all phone, TV, Internet signals from multiple customers travel in the same pipe to the collector node. It’s a very big pipe, but there is a maximum data rate and theoretically one customer’s service can slow down if others are heavy users at the same time. Cable does not slow down much due to distance. AFAIK, most cable now uses fiber to the curb (but not to the house). Older systems may use coax (copper).
DSL: Offered by telephone carriers. A dedicated line to the Central Office only, so your neighbor’s activity has no effect on your speed or thruput. Severely limited by distance and the max speed available drops off rapidly after the first 1000 ft from the CO, making any run longer than 3 miles or so (counting the distance up and down poles) impractical (why use DSL if it is only dialup speed?) AFAIK, most telephone companies use fiber only to a CO or node, then copper to the neighborhood and homes; copper that may have been strung decades ago, so telephone technology is behind cable in this area.
From what I’ve heard, DSL and cable are roughly equivalent in overall throughput and in areas where both are provided, compete for the same customers, so their prices are similar.
Someone else more knowlegeable than I will have to verify this, but I always assumed the reason DSL was faster than twisted pair is because it uses several twisted pairs at once in sort of a semi-parallel data arrangement. Otherwise, it would have to be a different kind of cable altogether.
DSL operates over twisted pair, the same kind of twisted pair used for POTS (plain old telephone service). It can do this because the typical twisted pair loop between a subscriber and the central office actually has much more bandwidth than is needed for POTS. DSL only needs a single pair (two wires).
No, it’s a bandwidth limitation–see my previous post. Voice and standard dialup analog data transmission is limited to just over 3 kHz of bandwidth. But unshielded twisted pair is capable of carrying in excess of one megahertz of total bandwidth over a few tens of thousands of wire feet; longer distances reduce this figure. DSL uses this extra bandwidth to transmit data at high speeds.
Coaxial cable can carry several hundred megahertz of bandwidth, but it also has to carry a lot more information since it needs to also transmit the video and audio information for upwards of a hundred TV channels, in addition to the digital information. If cable carried only your internet data, it could easily exceed the DSL speed by several orders of magnitude.
Then, Mks57 and Q.E.D., what I don’t understand is if one twisted pair can provide DSL-type speeds, why is a typical household served by a single twisted pair limited to 56K? Are all twisted pair wires the same?
If distance only, could a customer very near a CO (<1000 ft) get fast speed with only POTS (and an appropriate modem)?
Because that’s about as fast as you can send information using the ~3 kHz of bandwidth that dialup modems can make use of.
OK, so if it wasn’t for the narrow audio-range limitation, any consumer connection (not too far from the CO) could achieve DSL speeds?
Well, yeah, sorta. But then it wouldn’t be POTS anymore. It would be DSL.