Refers collectively to all types of digital subscriber lines, the two main categories being ADSL and SDSL. Two other types of xDSL technologies areHigh-data-rate DSL (HDSL) and Very high DSL (VDSL).
ADSL Defined
ADSL is the most commonly deployed types of DSL in North America. Short for asymmetric digital subscriber line ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate). ADSL requires a special ADSL modem.
SDSL Defined
SDSL is still more common in Europe. Short for symmetric digital subscriber line, a technology that allows more data to be sent over existing copper telephone lines (POTS). SDSL supports data rates up to 3 Mbps. SDSL works by sending digital pulses in the high-frequency area of telephone wires and can not operate simultaneously with voice connections over the same wires. SDSL requires a special SDSL modem. SDSL is called symmetric because it supports the same data rates for upstream and downstream traffic.
Two other types of DSL technologies are High-data-rate DSL (HDSL) and Very high DSL (VDSL). VDSL offers fast data rates over relatively short distances - the shorter the distance, the faster the connection rate. Collectively, all types of DSL are referred to as xDSL. HDSL (High bit-rate DSL) is the earliest variation of DSL to be used for wideband digital transmission within a corporate site and between the telephone company and a customer. The main characteristic of HDSL is that it is symmetrical: an equal amount of bandwidth is available in both directions. For this reason, the maximum data rate is lower than for ADSL. HDSL can carry as much on a single wire of twisted-pair as can be carried on a T1 line in North America or an E1 line in Europe (2,320 Kbps).
Cable vs. DSL: The Speeds
The topic of "which is better and faster" has been a highly debated topic. Historically, DSL speeds have been slower but new technology lessons the speed gap between DSL and Cable Internet. DSL offers users a choice of speeds ranging from 128 Kbps to 3 Mbps. Cable modem download speeds are typically up to 2 times faster than DSL. The important thing to note about cable Internet connections is that cable technology is based on shared bandwidth with many factors influencing a users download speed. With shared bandwidth the speed fluctuates depending on the number of subscribers on the network.
With DSL, the connection is yours and not shared, and you tend to have a more constant speed. This is one reason why cable Internet providers don't often publish speed information or use phrases like "with speeds up to..." instead of listing something a little more precise and numerical. In more rural areas with fewer subscribers, you're bound to have faster download speeds than a subscriber in a metropolitan center.
Because cable modem speeds fluctuate, it is difficult to gauge an exact download speed. On the upload stream, however, cable and DSL are closely matched for speed. Both DSL and cable Internet speeds are largely dependant on the service provider and either the distance away from the switching station you are or how many subscribers are in your immediate area.
Cable vs. DSL: The Price
The price consumers will pay for DSL or cable Internet services is not standard. It depends on how much competition there is for broadband services, and the area you live in. For example, in some areas it's only been in the past few years that cable Internet has been available. Until then, DSL costs were quite high, but as cable Internet became available the price of DSL went down. With either option you generally will pay a one-time set-up fee. For cable you could expect this fee to be anywhere from $50 to $100, while the cost for DSL installation is usually a bit more and could run up to $150 for set-up. Once the installation is completed, you will usually pay for your Internet subscription on a monthly basis. Cable, again, is usually a bit cheaper with monthly fees averaging $40 to $50. You can expect to pay about $5 to $10 more a month for DSL service.
If you live in an area where both cable and DSL is offered then you may find yourself being able to nab a better deal on your broadband service. Your local DSL or cable carrier may offer introductory offers such as free installation or offer the Internet service free for a couple months. In addition, you can also check and see if the service provider offer discounts on service bundles. For example, many cable companies offer discounts for "surf and watch" which gives you a price discount if you subscribe to both cable TV and cable Internet from the same provider (also many cable operators now offer VoIP capabilities as part of the mix). If you choose DSL you may qualify for a "surf and talk" bundle plan.
Remember that broadband Internet connections are a highly competitive market, so if you are switching between service providers always inquire about waived set-up fees and introductory subscription rate specials.
Did You Know...
In "perfect" conditions, cable download speeds are up to 2 times faster than 1.5Mbps DSL speeds, Which is roughly 50 times faster than 28.8K Modem.
DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations.
xDSL is similar to ISDN inasmuch as both operate over existing copper telephone lines (POTS) and both require the short runs to a central telephone office (usually less than 20,000 feet). However, xDSL offers much higher speeds - up to 32 Mbps for upstream traffic, and from 32 Kbps to over 1 Mbps for downstream traffic.
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