Digital Subscriber Line (DSL) Versus Cable
This chapter is from the book
This chapter is from the book
This chapter is from the book
Broadband Internet connectivity: If you have a need for speed and the World Wide Wait is driving you crazy, it could be the answer to your prayers. But there are choices to be made. This article is going to talk about the good, the bad, and the ugly of cable modems versus DSL—with an emphasis on what you can get.
DSL is a faster Internet connection over standard telephone wires. In concept, it's like ISDN but a lot faster. For example, you can get DSL service from AT&T or from other ISPs.
The main competition for faster surfing is cable modem service. You can now connect to the Internet using exactly the same cable that you probably have hooked up to the TV.
You want hype? Cable companies point to speeds of 50Mbps (700 times faster than the fastest analog modem) when they talk about their technology. They brag that each standard TV channel offers 8Mbps of capacity and that they can put 80 to 100 channels on their cable. DSL vendors reply that you can download at 9Mbps over standard twisted-pair (telephone) wire (plenty for full-motion video) and that even higher speeds are possible.
The truth: In the future, they're both likely to run at about 3.7Mbps, for all practical purposes. And even then, you will probably be server-bound and won't be able to approach the top speed. Nationwide, the phone companies sell DSL in three standard speeds: 256Kbps, 512Kbps, and 768Kbps (depending on your supplier, you can buy DSL service from an ISP other than AT&T). Cable already runs at a download speed of 3.7Mbps, but only at 128Kbps upload. But, hey! That's still as fast as ISDN!
Cable types tell you that only they can provide high bandwidth at an affordable price now because DSL is just not widely available yet and has a lot of technical problems. True, cable modem digital service is about 12 months ahead in most markets. Is that too long to wait? Most forecasters predict that DSL will catch up fast. And cable modems have a few technical problems of their own.
Technology Issues
What is DSL? How does it work? What are the types of DSL? These are some of the questions that this article will surely answer, as well as give some of its pros and cons.
DSL: What Is It?
In essence, by using the existing telephone cabling infrastructure, DSL is a technology backed by telephone enterprises that provides high-bandwidth services to the home and enterprise. Because DSL utilizes a greater range of frequencies than ordinary dialup services (allowing for a much faster connection), this high bandwidth is possible. For most providers, this technology is still in the early stages of rollout.
How Does It Work?
The general idea behind DSL technology is relatively easy to grasp, even though it is rather sophisticated. As previously mentioned, DSL utilizes a large range of frequencies, which means a higher bandwidth and a faster connection speed. For example, consider this: Only a small fraction of your phone line capacity (bandwidth) is being used (that being only the low frequencies) when you make an ordinary telephone call. By transporting data into the higher frequencies, DSL takes advantage of this idle bandwidth. This results in making it possible for you to talk on the phone and be on the Internet simultaneously via the same line.
DSL Types
As shown in Table 1, there are several competing forms of DSL, each adapted to specific needs in the marketplace. Some forms of DSL are widely used standards, some are proprietary, and some are simply theoretical models. They may best be categorized within the modulation methods used to encode data. As previously stated, Table 1 shows different types of DSL technologies. These technologies are sometimes collectively referred to as xDSL.
Table 1 The Many Flavors of DSL
|
Type |
Description |
|
ADSL |
Asymmetric Digital Subscriber Line. The most common standard, it theoretically offers 1.5–8Mbps downstream and 16Mbps–640Kbps upstream speeds. |
|
HDSL, HDSL2 |
These two high-data-rate DSLs are symmetric services capable of 1.5Mbps and 2.048Mbps speeds, respectively. HDSL requires two or three-wire pairs; HDSL2 requires just one pair. |
|
IDSL |
ISDN DSL. Similar to ISDN, it allows you to use existing ISDN equipment. But the maximum speed in both directions is 144Kbps. |
|
RADSL |
An asymmetric service, rate-adaptive DSL promises to provide speeds of 8Mbps–600Kbps downstream and 1Mbps–128Kbps upstream, while offering simultaneous voice service. RADSL can dynamically adjust to line conditions. |
|
SDSL |
Symmetric DSL, a popular alternative to ADSL, is offered by various ISPs, including NorthPoint 1. The service promises two-way 768Kbps access. |
|
G.Lite (UADSL/DSL-lite) |
G.Lite is user-installable and provides speeds of 1.544Mbps downstream and 512Kbps upstream. It is backed by many hardware vendors and the Universal ADSL Working Group 2. |
|
VDSL |
The fastest and newest DSL on the block, very high-speed DSL is an asymmetric service, offering speeds of 12.9–52.8Mbps. |
Again, as explained in Table 1, Asymmetric Digital Subscriber Line, or ADSL, is the most popular form of DSL technology. The fact that the upstream and downstream bandwidth is asymmetric, or uneven, is the key to ADSL. In practice, the higher-speed path will be the bandwidth from the ISP to the user (downstream). This is mainly due to the desire to accommodate the typical Internet usage pattern, where the majority of data is being sent to the user (Web pages, graphics, programs, and video) with minimal upload capacity required (keystrokes and mouse clicks). Speeds typically range from 1.5 Mbps to 144Kbps downstream. Table 1 has also shown that there are other forms of DSL as well: ADSL Lite, Consumer Digital Subscriber Line (CDSL is a proprietary technology trademarked by Rockwell International 3), G.Lite, HDSL, IDSL, RADSL, SDSL, and VDSL. Many of these forms are just starting to become available through the telephone enterprises, and some of them have just completed the testing/development stages and are expected to offer the technologies soon.
DSL Versus Cable Modems
Cable modems, although capable of high potential access speeds, have drawbacks. Primarily, the signal is shared between the subscribers in a specific area, and the technology is broadcast-oriented. In other words, less bandwidth is available to each subscriber as the number of subscribers increases in that area. Moreover, cable access offers the user no choice regarding providers and is available only in a limited area. It is available only through the cable enterprise, which has demonstrated little experience with Internet services.