Digital Subscriber Line (DSL) Versus Cable

By John Vacca

Date: Dec 14, 2001

Sample Chapter is provided courtesy of Prentice Hall.

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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.

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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.

Current State of Cable Modem Access Versus DSL

So what's holding up DSL and cable modem access? If you have been told that the lack of widely accepted standards is the main factor delaying cable modem and xDSL access, think again. Lack of standards is, at most, a minor factor in the delay of widespread access.

Because solid standards have not been established, xDSL and cable modem access are being held up. So, let's put things in perspective, even though it is certainly true that the lack of standards is having some effect.

Cable modem and xDSL services are dedicated subscriber services. You use your cable modem or xDSL box to connect to one place—your service provider. You do not carry it around with you like a modem. Where you expect to move the device from place to place or to a different service provider (as with a 56K or 33.6 modem), standards affect only the end user in cases. Your cable modem or xDSL box is like your television cable box (which you never move—you buy it or lease it with the service, and it stays with the service), not like your modem. By allowing vendor competition, it is true that standards will lower hardware costs a bit. This, in turn, will lower your equipment costs, but not much. The important thing is that if your provider can offer you service at a price you like, that is what matters most to you. The fact that he or she will be able to buy the box that he or she leases to you for $10 a month for $100 less next year is simply not that much of an issue. Anyway, it's probably a small fraction of the overall cost of providing the service.

The history of cable modem access by Cablevision ⁴ on western Long Island over the last several years tends to support this. The original beta access used a specific brand of cable modem (which was provided with the service). When the beta program ended, the original equipment was discarded in favor of a newer, higher-performance product made by LanCity ⁵. This didn't affect end users much—they just returned the original modems and installed the new ones. The current service provides a 10Mbps Ethernet connection for under $70 per month (this includes the lease of the cable modem unit, connection, and ISP service) for residential customers. This service is about three to five times faster than a full T1. The LanCity cable modem follows the only real standard that matters so far—it connects to the user's PC using standard 10Mbps Ethernet like most other xDSL units and cable modems.

You'll have to look elsewhere than the lack of widely accepted standards if you want to know why xDSL and cable modem service is slow in accessing. Maybe you should wonder whether the cable enterprises are simply afraid of moving into a new technology that they don't understand, whether the telcos aren't that eager to access a DSL service in direct competition to their data T1 and T3 services (and with a lower price tag), and whether anybody has enough backbone capacity to support the large numbers of high-speed customers that the new service would attract. Incidentally, Cablevision claims no immediate plans to offer enterprise services. It is not interested in going outside its traditional market to offer service to more demanding enterprise customers (who generally use a higher percentage of the available bandwidth for a larger part of each day than residential customers).

Nevertheless, the battle for broadband data services to the home and enterprise has been played out as a battle between the telephone enterprise (telcos) and the cable operators. The battle has been fueled by "arms merchants," the silicon suppliers and xDSL and cable modem box vendors, selling both hype and product to both sides. With over 470,000 in commercial operation in North America alone and the entire industry rallying around CableLabs ⁶ promulgated standards and retail distribution models, cable modems have taken the early lead. A tremendous lure for the cable operators is the potential for remote LAN access and IP telephony on top of Internet access. Meanwhile, in an attempt to solidify the industry and to catch up with cable deployments, the DSL community is moving toward a low-cost, splitterless G.lite standard. G.lite could be an easily deployed, low-cost technology that carries a dedicated IP pipeline on top of the twisted-pair voice connection leading into virtually every home. G.lite could also be just another vegetable in DSL alphabet soup. The major regional Bell operating companies (RBOCs) have recently announced DSL access plans for 2000–2001, despite a myriad of technical and enterprise hurdles.

So what's real, and will there be a winner in this battle for broadband in the local loop? Well, a recent bitter struggle among equipment manufacturers is threatening new industry rules that could make broadband in the local loop or high-speed Internet connections less expensive, easier to use, and available to far more people.

DSL Progress Is Thwarted

The infighting centers on the so-called G.lite standard, which is designed to simplify cable modems used for digital subscriber line (DSL) connections. Thus, manufacturers need to make products that can work together seamlessly to speed wide-scale adoption of DSL because the market is littered with different technologies.

This type of conflict is common with emerging technologies, but rarely are the stakes as high as they are today. High-speed access is largely associated with the growth of the Internet itself, and billions of potential dollars hang in the balance for those enterprises that come up with the winning solutions to break the widespread bottlenecks across the Web.

Moreover, the rhetoric is particularly rancorous in the G.lite debate. Critics say that G.lite modems do not work well with current technology, according to service providers, and some manufacturers are now fighting to see their own products adopted as the industry standard.

In some cases, these technologies can't even communicate. It's not just that you need a G.lite modem. You need a G.lite modem from a specific manufacturer. And that's the same as no standard at all.

While equipment makers argue over how to best implement the G.lite standard, competition from high-speed cable modems is intensifying. The cable industry has already established a standard set of rules for cable modems, giving the group a leg up on its DSL rivals.

According to TeleChoice ⁷, about 380,000 DSL lines were in use by the end of the last quarter of 1999, with 86% of these in residences. Cable modems have reached well over three million users.

Just as telephone enterprises and Internet service providers such as America Online ⁸ and Prodigy ⁹ ramp up their marketing machines to push high-speed Net services across the country, the lack of a universally accepted standard could slow the spread of DSL. To have an absolute standard that leaves no variation in the way that equipment vendors can make their equipment is not practical.

All in One

So that different enterprises create products that can work with each other, many industries push for technology standards, or rules. For instance, VHS is a standard for videotape. Regardless of the enterprise that manufactured the VCR, a VHS tape cassette will play on any VCR machine that is built to handle that certain type of tape.

Standards are critical in the communications world. If a consumer buys a modem, it must work with his or her computer as well as the ISP.

You can't get to the point of popularity reached by ordinary analog modems without a standard. For example, people should be able to buy a computer at CompUSA ¹⁰ or a similar store, take it home and plug it in, and have it work with their ISP.

Several years ago, the Internet and computer industries coalesced around the G.lite standard for consumer DSL. It was ratified by the International Telecommunications Union ¹¹ as the worldwide set of official technical guidelines.

Rather than wait for a phone enterprise technician to install a modem, the standard is aimed at making DSL relatively cheap because it would allow a consumer to buy a modem and plug it into a PC. The challenge is to make sure that modems and other equipment made under the G.lite standard all work together.

Lab Tests

The University of New Hampshire ¹² has set up a lab where enterprises such as Intel ¹³, Alcatel ¹⁴, Lucent ¹⁵, and others can test their modems against each other and against other products—all under the auspices of the ADSL Forum. Nevertheless, some enterprises already say that they comply with the standard, and some computer makers (led by Compaq ¹⁶ and Dell ¹⁷) have already begun shipping machines with standardized DSL modems that conform to G.lite rules. However, the modems still won't work with all ISPs and telephone enterprise equipment.

The big telephone enterprises (the enterprises that will invest the most money in DSL equipment), for their part, are testing G.lite technology and hope that manufacturers will end their differences as soon as possible. Most phone carriers are using different versions of DSL on an interim basis in the meantime.

This has taken the interoperability process to a whole new level. It will take time to sort it out.

So, how prevalent are cable modems and DSL in major U.S. markets? Let's take a look.

Prevalence Of Cable Modems and DSL in Major U.S. Markets

Cable modems and DSL are somewhat prevalent in major U.S. markets. They are, nevertheless, a quantum leap in Internet access, putting an end to the World Wide Wait.

All the hype about instant information on the Internet doesn't mean much when you've got a Web page downloading so slowly that you have to keep yourself busy by flipping through the Sunday paper or glancing at the headlines on CNN. There's an apt, if overused, name for this trickling of info: the World Wide Wait. As previously discussed, now two competing technologies (cable modems and DSL) would like to bring high-speed Internet access into your home, ending the wait with speeds up to 300 times faster than what's possible with standard modems. For as little as $40 per month, these next-generation methods of connecting to the Internet promise to transform the cyberspace experience. Think video-on-demand or live stock tickers. Both are possible if you've got the bandwidth or connection speed.

Chances are, however, such access is not available in your area yet; cable enterprises, phone enterprises, and Internet service providers are in the early stages of offering cable modems and DSL. If you have access to one, you are considered one of the lucky ones. If you have a choice between the two, you're very, very lucky. But DSL launches are under way or planned by Bell Atlantic ¹⁸, GTE ¹⁹, and U.S. West ²⁰, and with cable enterprises expecting competition from DSL, you're likely to hear about high-speed access coming to the home of a friend—and maybe even your own.

Skeptical? Witness AT&T's ²¹ acquisition of cable TV giant Tele-Communications, Inc. ²², a merger spurred by the prospect of offering new services (and packaging existing ones) through high-speed lines into the home. The deal was a $70 billion vote of confidence in the Internet's transformation from a frequently slow and frustrating means of communication into a mature, consumer-friendly medium. Other providers now have a newly energized mega-competitor in this arena, and that's likely to mean a faster rollout of high-speed access.

But just in case you think this is another overhyped upgrade, like the much-ballyhooed 56Kbps modem, think again. The advances in standard modems have been incremental: from 14.4Kbps to 28.8Kbps to 33.6Kbps to the current champ, 56Kbps. Supercharge all that, and imagine the switch from 33.6Kbps to, say, 1.5Mbps. That's 45 times faster, meaning that a 5.6MB game would take about 30 seconds to download instead of 22 minutes. Or, the hundreds of pages you're viewing in a single session of Web browsing will appear without delay, as if the pages were stored on your hard drive. Aside from speed, both cable modems and DSL offer another advantage: an always on connection to the Internet that doesn't tie up your phone line. There's a lot of pent-up demand for this.

To check on availability, call your local cable enterprise or (for DSL) the phone enterprises and Internet service providers in your area. Costs can vary wildly because most high-speed-access providers currently face no competition. Cable modem access typically runs about $30–$50 per month; DSL is costlier, and its pricing is more complex. For cable modem access, local cable systems package an Internet service provider (@Home ²³ is the leader) with the speedy line into your home. With DSL, you're likely to have the option of choosing an Internet service provider and the level of speed, from around 256Kbps on up. Not all ISPs offer DSL or cable modem options yet, so check with your current provider to see if high-speed access is available.

Consider the DSL offerings of U.S. West, now available in 60 cities, including Denver, Phoenix, Salt Lake City, and Minneapolis–St. Paul. For $40 per month, you'll get DSL that runs at 256Kbps, or you can combine it with U.S. West Internet access for $59.95. Want more speed? Like 512Kbps? That will cost you $65 a month, plus $39.95 for Internet access. Other DSL providers have similar plans, commonly offered in tiers for casual users and enterprise customers. For the time being, at least, cable modems may be considered the better value.

Expect to pay installation fees of up to $250 for either one; a technician has to visit your home to handle the wiring. A high-speed-access modem may cost as much as $300, but some providers may have a rental option or even include modem fees in the monthly rate.

Problems? The biggest headache is that it's not available in all areas yet and, more importantly, may not be available in your area.

Nevertheless, will DSL service for faster access to the Internet catch on with enterprise users? Analysts say that it will, but users aren't as sure.

Unsure Users

Many telecom managers are still waiting for the success stories with DSL technology. Several respected consulting enterprises have projected phenomenal growth in DSL technology and service. Gartner Group, Inc., in Stamford, Connecticut, predicts annual growth rates of more than 500%, with more than 3 million DSL lines installed by 2003—up from fewer than 70,000 now. Analysts' confidence in the market's growth is based on the strong need for faster connections to the Internet sought by consumers and enterprise users who telecommute or work in remote locations.

Benefits

The most-discussed variant of DSL, Asymmetric DSL (ADSL), boasts downstream speeds that are more than 50 times faster than 56Kbps connections. But analysts say the upstream speeds are much slower, making ADSL less attractive for enterprise users who need to push large files to colleagues and enterprise partners.

Several carriers are deploying or testing Symmetric DSL (SDSL) to solve the need for fast upstream speeds using equipment by start-up vendors such as AccessLan Communications, Inc., in San Jose, California, or Copper Mountain Networks, Inc., in Palo Alto, California. Established networking vendors such as Cisco Systems, Inc., ²⁴ and Bay Networks, Inc., ²⁵ have also entered the arena.

Competitors in the SDSL market hope to attract customers with lower price and convenience of installation, compared with installing T1 lines. AccessLan will give enterprises a 1.5Mbps SDSL connection at lower cost than a typical T1 (1.544Mbps) connection from a telephone enterprise. Therefore, if DSL spreads as quickly as anticipated, there will be pressure on telcos to reduce their T1 prices.

Another factor is how long it takes an enterprise to install its own on-premises SDSL equipment, compared with waiting for a T1 connection. With SDSL, a small router is installed at the enterprise and an access concentrator is installed in a carrier's central office. The two are connected by existing twisted-pair phone cable. The process may take only a day, compared with waiting, in many occasions, several weeks for a carrier to install a T1 line.

Most users would consider using cable modems for faster speeds, if they were available. Cable modems won't have as much growth among enterprises as DSL, partly because office parks often are not commonly wired for cable.

Comparison of Cable Modem Versus DSL: Speed and Cost

When compared to DSL, the cable modem has few advantages and several disadvantages for Internet access. DSL, on the other hand, has many advantages. Unlike ISDN, DSL isn't metered by the minute. Better yet, DSL is truly an always on service, which makes it suitable for a wider range of applications, including interconnecting LANs, Web site hosting, videoconferencing, and connecting branch offices (see Tables 2 and 3).

Table 2 DSL Versus Cable

Benefit	DSL	Cable Modem
Consistent download speed	Yes	No
Consistent upload speed	Yes	No
Immune to degradation from	Yes	No
neighborhood usage
Secure, exclusively dedicated	Yes	No
line with isolated data
Carrier guarantees performance	Yes	No

Table 3 High-Speed Services Compared

	ISDN	T1	DSL
Speed	128Kbps	1.544Mbps	128Kbps to 1.544Mbps
Cost per month	$60–$120	$800–$3,500	$89–$425,
(including Internet service)	for moderate usage		depending on speed
Notes	Per-minute charges make full-time connections impractical.	Price can vary with mileage, usage, and service level.	Wide spectrum of services; distance limitations; incompatible versions.

Performance

In every cable modem network neighborhood, hundreds (perhaps thousands) of households all share a common transmission medium. Download speed could be high if conditions are optimal with absolutely no activity from neighbors. However, typical download speeds in many neighborhoods are no higher than 400Kbps range during real-world usage. Upload speeds are even slower because the cable modem network is optimized in one direction only and, depending on cable provider, is often capped.

Value

As more users pile onto cable modem services, performance goes down rapidly, diminishing the value of the service. In response, many cable modem providers around the country now cap subscriber outbound speeds at 128Kbps (equivalent to about two 56K modems). DSL is immune from both real and artificial speed restrictions. The quality and value of DSL remains constant for the lifetime of the service, while cable modem Internet quality degrades and loses value over time. Combine that with a yearly term requirement imposed by the cable modem enterprise with each subscription, and you may discover that you are locked into a losing investment.

Security

Aside from performance variations and diminished quality, the shared cable modem network also introduces concern for security. Data from one household passes over the same wire connecting others, potentially exposing credit card, email, and other sensitive data. For this reason, users either find cable Internet access unacceptable or must arrange encrypted software tunneling to secure networks, which impedes performance.

No Surprise Here

Not surprisingly, DSL use is expected to boom. According to market research analysts at TeleChoice ²⁶, the number of installed DSL lines is expected to grow from 566,000 in 2000 to 2,126,000 in 2002, to 4.57 million by 2004. DSL is expected to do well among people working at home (telecommuters) and in urban areas where cable services are not widely deployed.

Residential Users

Residential cable modem service can be a good value for high-speed access. Still, there are some limitations for residential cable modem service, as mentioned earlier. Cable is a shared medium, unlike DSL, which offers a dedicated line for each user. When too many users in one neighborhood try to share the same cable, performance suffers dramatically as users compete for the limited resources that one cable can afford. For this reason, residential cable customers are basically prohibited from telecommuting, hosting Web sites, and using video teleconferencing and any other bandwidth-intensive applications. The security problems of using a shared medium makes cable modem users much more vulnerable to data interception, unauthorized monitoring, and hacking from other users along the same cable network. While there is a market for residential cable modem service, obviously there can be some significant drawbacks.

Telecommuters

Telecommuters using cable modem service are required to pay a rate that is generally designed for the few enterprises that have cable modem service available. Service packages start at almost double what a DSL telecommuter would pay for the same speeds. Additionally, cable telecommuters are subject to the same security and bandwidth problems that residential cable customers face. Therefore, cable modem service is not a particularly attractive option for these customers.

Choices

Although the number of enterprises supplying DSL service and Internet access is increasing, would-be users face a confusing range of choices about availability, price, equipment, and configuration. DSL service is hardly ubiquitous. Even in areas where DSL has been deployed, if you're too far from the phone enterprise's central office (where the switching hardware is located), you can't get it or you don't get the maximum possible speed. Prices, while reasonable for enterprises, are steep for individuals. 128Kbps service can cost as little as $89 per month, while 1–1.544Mbps service can go for several hundred dollars. Equipment is not widely standardized, and there are a number of DSL variants to contend with (see Table 1).

So, what are the planning implications for the enterprise network manager? Let's take a look.

Planning Implications for the Enterprise Network Manager

For the enterprise network manager, operator, and service provider, it is now an accepted, inescapable conclusion that xDSL technologies will one day be installed on a global basis in vast quantities. Despite other technology developments (not excluding recent announcements about the commercial viability of sending data down power lines), it is still the only viable technology capable of substantially increasing bandwidth on the local access loops without a substantial overhaul. These copper loops are ubiquitous over every home, and it is unlikely that any mass-scale upgrade to fiber will happen within the next decade.

The primary driver for xDSL is high-speed Internet service deployment to residential customers. So far, there have been two small commercial deployments and no less than 66 trials around the world, trying to prove that asynchronous DSL (ADSL) can provide a downstream connection of up to 8Mbps and upstream connection of up to 1Mbps over the existing telephony copper pair.

Both IP and ATM network architectures are currently on trial. ATM is considered the probable choice in the future. Initial trials have used standalone ADSL modems with discrete IP interfaces for reasons of time to market and availability; these are evolving to highly integrated digital subscriber loop access multiplexers (DSLAM) solutions.

The complete network typically consists of a core that is based around Synchronous Digital Hierarchy (SDH), wrapped with broadband ATM switches, ATM access switches, and DSLAMs. The DSLAMs provide the individual xDSL lines out to the customer premises and integrate with the existing POTS network connections. But even after having been in trial for more than 18 months, few operators seem close to commercial rollouts. What is taking them so long?

Some of the main barriers to large-scale adoption include the continuing standards battle and the lack of interoperability. The existence of two de facto standards—namely, DMT and CAP—provides network operators with a dilemma: deciding which to adopt before a leader is clearly identifiable in case the choice ends up as the Betamax of the standards. There are two standard camps, one apparently led by Israel's Amati, which has developed modems using discrete multitone technology (DMT) for the line coding. Motorola ²⁷ and Alcatel ²⁸ are among the major manufacturers that have developed DMT modems. The second camp has adopted a technology developed by the former AT&T Paradyne, which championed carrierless amplitude modulation/phase modulation (CAP) for the line coding. Westell, the enterprise that made the ADSL modems being used in Bell Atlantic's Virginia trial, uses CAP. With no clear stance being taken, a general "wait and see" attitude is developing.

Lack of interoperability is also becoming a matter of concern. The current xDSL units on the market, from a variety of vendors supporting different standards, do not interoperate. Interoperability between vendors' equipment is key to mass rollout and provisioning. The ultimate goal is for the end customers to be able to purchase their own ADSL termination units, much the same way as people buy off-the-shelf analog modems today. For this to happen, the ADSL termination unit technology needs to mature to the point that it is as simple as a modem to install and operate.

Operators are still deciding on suitable end-to-end architectures. Once these infrastructures have been agreed upon and the business and technology are in place, services can then be rolled out in volume. These new architectures need to address the integration of network, service, and enterprise management of these new broadband services. Without these seamless, end-to-end management systems in place, it is difficult to see how operators will be able to make any profit on broadband services.

Enterprise Network-Management Capabilities

The new broadband services being deployed by enterprise network managers, operators, and service providers are typically delivered over very complex network environments that include legacy equipment with primitive management capabilities and newer systems incorporating sophisticated telecommunications management network (TMN)–based element management. New network-management infrastructures are required to mold these disparate information sources into a cohesive view of the end-to-end services being delivered. This can be complicated by the large scale of such services—typically involving hundreds of thousands or millions of network elements. The major requirements can be summarized as follows:

• Cost-effective performance scalability—A system has the ability to manage small pilot networks and expand as the network grows without performance degradation.

• Multiple protocol support—Standards-based and proprietary management protocols must be supported in a transparent manner to the network applications.

• Powerful event management—As the network grows, the number of events grows exponentially. The ability to manage this volume of events in a way that helps the operator make sense of the status of the network is mandatory.

• Seamless application interworking—Operators will use a number of different applications to manage aspects of the network, but they require the ability to move easily between applications—to investigate problems or configure service for a particular customer, for example.

• User access management—The information within the management system must be protected, but it must also be feasible to partition the data and the access to it in a way that supports operational processes.

Enterprise Network-Management Architecture

Some of the key management challenges when installing xDSL networks include potential element volumes. xDSL network elements are extremely complex devices that require real-time management. As element volumes increase exponentially, operators are faced with the challenges of implementing end-to-end systems that can manage millions of highly complex access elements.

As an example, the 1994 BT video-on-demand (VOD) trial supported 2,000 ADSL lines, equating to 4,000 access elements. Although this was classified as a small marketing trial, it is still the largest single xDSL installation in the world. This network generated a tremendous amount of management traffic, primarily with SNMP and performance-monitoring information, all of which had to be processed in real time by the central management workstation.

Additionally, xDSL equipment, by virtue of its inherent built-in intelligence, generates a tremendous amount of management traffic. This information, be it alarms, performance-monitoring information, configuration data, diagnostic commands, or inventory data, has to be processed, stored, prioritized, formatted, and displayed by the central management console. A single element-management workstation cannot scale to support any major network growth.

Element and network complexity is also an issue that operators need to prepare for. xDSL equipment is becoming more complex with each generation. The latest generation uses rate-adaptive transmission, which causes a myriad of possible upstream and downstream speed permutations. Remote equipment now incorporates xDSL transmission hardware, IP routing equipment, and IP or ATM CPE interfaces into a single unit. In addition, it has to be seamlessly integrated with the existing POTS network leading to a wealth of configuration permutations, performance monitoring information, alarm and event reports, and diagnostic functions and inventory data being available to the network operator.

A typical end-to-end network capable of delivering high-speed Internet, on-demand services, and data and voice from multiple service providers is extremely complex. Many issues can be resolved only with the use of integrated management applications and systems. This often results in a number of incompatible element-management systems being installed to manage different parts of the network and then integrated together to provide an overall end-to-end service-management system. The eventual goal is to provide a zero-touch system to allow the end customers to control and manage a large part of their own service offering in real time.

xDSL equipment is normally installed over existing telephony circuits, but the devices at each end of the connection contain POTS splitters that allow both the telephony circuit and the xDSL circuit to use a single copper pair. This requires the integration of a new xDSL management system with existing POTS systems.

A range of issues also clouds the most efficient interface for the customer premises equipment. The two protocols in question are IP and ATM. Network operators are installing complex networking equipment into residential environments for the first time. This can lead to a multiplicity of new problems. These problems range from units being tampered with and cables being disconnected, to PCs being reconfigured. This could result in a huge increase in the number of service-related calls and queries directed at the network operator. The operator has to be able to diagnose, isolate, and analyze problems from the central management system. Only when this type of network, system management, and control is achieved will broadband services become commercially viable.

Viability

The density of the technology must increase dramatically to enable operators to fit all the required ADSL termination units into their existing exchange real estate. xDSL technologies are still costly, and this is holding back general acceptance due to the costs of equipment investment and the ongoing line-rental charge. Prices in the range of $370 to $420 would start to approach an acceptable level for the benefits of this new broadband technology.

In most European countries, however, high-capacity broadband ATM backbone networks have yet to be deployed. Without this backbone infrastructure, there is little benefit to be gained from introducing an upgraded access network. In the infrastructure context, the questions of how some major European operators will play off ADSL against their substantial ISDN services will be an interesting debate. As it now stands, current versions of ADSL cannot coexist with ISDN BRI lines. New versions of ADSL are being developed that will coexist with ISDN, but, as yet, they are available only in small trial volumes from less than a handful of vendors.

Telecommunication enterprises such as Deutsche Telekom ²⁹, which bet its future on ISDN, are now involved in desperately trying to increase ISDN usage before ADSL establishes itself. The situation it faces (in common with many other operators in Europe) is that too much emphasis and keenly priced ISDN will undermine ADSL; at the same time, not investing an adequate amount of resource on ADSL now might undermine its future as a broadband services provider.

So, what does the future hold for DSL and cable modems? Let's look at DSL first.

Future of Cable Modems and IDSL

From the point of view of a commercial (profitable, both for provider and user) service provision, xDSL can be considered an immature technology. xDSL has been proven an effective, reliable solution in many international trials. However, it is developing and progressing continually. This adds to the xDSL management complexities requiring the facilities for operators to download new algorithms on a regular basis.

xDSL standards are relatively new and are, therefore, prone to change on a regular basis. This involves regular, programmable equipment upgrades such as software download of new versions of xDSL transmission and application code from a central management station.

As with all new technologies, technical and cost issues do get resolved in subsequent generations. xDSL is no different. The market demand for high-speed, broadband communications will drive the development of the technology and will produce an economic, reliable solution for end users. For network operators, xDSL is the most cost-effective way of upgrading the copper infrastructure and competing against fiber and cable competitors. Another factor in determining market direction is the move for European PTTs (Post, Telegraph, and Telephones) from monopoly to deregulation and free competition. This will force network operators to unbundle their loops in a similar way to what has already happened in the United Kingdom and the United States. These new competitors will aggressively target end customers with offers of high-speed, broadband data communications, tempting them from the traditional service providers who may not be moving as quickly toward new service provision.

So, using the existing copper networks, xDSL will be made available, which will motivate PTTs to respond, eventually leading to a critical mass and explosion in xDSL deployments. While network operators, service providers, and vendors debate the standards, technology, and cost issues of deploying xDSL networks, customer demand is growing for cost-effective, high-speed, broadband networks that unleash new services and new business potential for them. Looking at the rapid development of Internet and intranet business and services over the last few years, one can expect resolutions to the main issues and mass xDSL deployment within the next three to five years.

On the other hand, cable modems will dominate the North American residential Internet access market by 2004, outpacing digital subscriber line (xDSL) lines six to one, according to a new market study conducted by Forward Concepts, Inc., a Tempe, Arizona–based consulting and market research firm. More than nine million cable modems are expected to be installed by then. By 2004, the base for worldwide residential broadband access is expected to be close to 40 million users, but that isn't enough to support everyone who wants a piece of the broadband market. The big losers in the push toward high-speed broadband data services will be the telephone enterprises if they don't depend less on lawyers and more on technology.

Cable modems will win out because unit prices will dip below $130. The average DSL modem pair will drop from about $2,200 to $90 in the same time frame, but questions still exist regarding whether DSL really works with existing telephone lines.

Some see the battle as being tipped in telephone enterprises' favor because customers will demand the dependable service they're used to having with their phones. Still, cable modem enterprises are, by default, winning the Internet access war among consumers because the phone enterprises have really not been as aggressive as they could be in offering high-speed broadband data services. However, it isn't too late for phone enterprises if they jump into the broadband market soon. Nevertheless, they will be shut out if they're not into volume shipments of xDSL by the end of the year 2001.

Thus, in the race to provide high-speed data access to Internet users, DSL will win over cable modems. That's because copper networks already are entrenched, and enterprises will want to leverage their existing investments in copper.

The tug-of-war between DSL and cable modems is a closely watched battle, and nobody knows for sure which side will prevail. The prediction of a DSL victory has less to do with the merits of DSL and more to do with the existing copper infrastructure.

Nobody has love or hate for DSL. They don't care, but it's got to be copper because you can't dig it up. What we have done with electronics for 30 years in communications is make copper more efficient. So, DSL is just an extension of a 30-year trend that won't stop.

It's too expensive to change the lines. As you get critical mass behind some of the vendors, DSL wins for sure.

DSL carries data at high speeds over standard copper telephone lines and allows users to surf the Net and talk on the phone at the same time, making it especially attractive for the home and small-office workplace.

Finally, cable modems are gaining popularity, and some heavyweight investors are betting on cable enterprises to provide expanded services in the future. Thus, confusion over standards, including ADSL, DSL Lite, and VDSL, poses an obstacle, but those issues should resolve themselves in 2001.

Conclusion

Depending on where you live, you might be able to get both cable modem and DSL Internet service for your PC. But coverage is spotty. The first thing to do is find out whether your house is covered.

Don't be surprised if you can get only one type of service where you live right now. In both cases, the phone companies have to install a lot of very expensive equipment before the service is available for you. If you live in any kind of a metro area, they'll get to you. Even if you don't, the chances are good that they'll still get to you.

Phone companies clearly understand that whoever gets to you first has a huge advantage over the other one, so they're all racing to complete their installations before they lose the market. They're playing for much more than just your Internet account. For example, AT&T recently bought a big cable company called Media One at a price that calculated out at over $5,000 per cable account.

One big reason they were willing to pay that kind of money is that they have a long-range plan to offer local telephone service through your cable connection as well. Yes, that's right. AT&T would have genuine competition for your local, not just long-distance, telephone business.

Have confidence. Corporate greed is on your side.

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