Will ADSL Supplant ISDN?
New high-bandwidth options may eventually compete against ISDN and coaxial cable
On the Internet, the quest for more bandwidth continues at an
ever frenzied pace. What started out as a text-only medium
has become graphics-intensive, with Java animations, sound and
even Quicktime movies. There are blinking logos, scrolling
text, and the prospect, at least, of thousands of other
applets that will download to your computer and run in
realtime. Previous articles in this Pacific Connection series
have looked at some of the high bandwidth solutions that go
beyond the 28.
Actually, ADSL is not new. The term was first coined in 1989 by Bell Communications Research (Bellcore), the research arm of the seven "Baby Bells" that were formed after the breakup of AT&T. The original conception for ADSL was to carry video- on-demand service to the home--a market that has so far remained dormant.. Meanwhile, ADSL has been given new life as a high-speed Internet carrier.
ADSL has at least two big advantages over ISDN: cost of implementation and speed of delivery. ISDN costs more to implement at the telephone central office--requiring new, expensive switching equipment. Not surprisingly, telephone companies don't want to make such an investment unless they are certain there is a demand. By contrast, ADSL deployment is relatively cheap.
ADSL--even at its slower speeds--is faster than ISDN for
ADSL provides asymmetric "downstream" transmission of between
While at first glance that might appear to be a problem, the fact is that the Internet bottleneck is largely unidirectional: a lot of data heads from Web servers to client sites, but relatively little data goes from users back to servers. The one notable exception: video conferencing. Even the prospect of Java applets coming into widespread use wouldn't much change this scenario. Imagine, for example, a Java applet in the form of a spreadsheet being downloaded to your computer. The way Sun Microsystems and other Java companies envision it, you might manipulate data on this applet locally on your machine to figure how to refinance a car loan. Only after this local manipulation takes place would you send any data back to the site. The applet itself travels strictly downstream and "dies" on the client.
Unlike cable modem technology, ADSL takes advantage of the existing infrastructure of twisted pair phone lines running to homes and businesses. There are only about 12 million homes worldwide that can support cable modem, compared with 700 million homes already wired for telephone. On the surface, ADSL's speed of 1-6Mbps might appear slower than cable's downstream bandwidth of 30Mbps--except that bandwidth is shared among many users on the line. Indeed, as I found out in talking to several prospective cable modem providers, it is difficult to get anyone to commit or agree to what coaxial cable actually delivers to the home.
ADSL--what is it?
ADSL was initially developed to distribute video in real-time
over ordinary telephone lines. But in 1995, it became clear
that the more viable application--at least for the short term-
-would be as a data communication technology. As such, ADSL
has been speeded up--from 1.
"ADSL went from a fixed speed to a variable speed, allowing phone companies to reach more people without having to change a line," said Kim Maxwell, chairman of the ADSL Forum. Maxwell predicts that ADSL will eventually serve 80 percent of subscribers with the existing telephone infrastructure, with the remaining 20 percent served by running a fiber optic cable from the central office to a remote node. Such a node would provide 6Mb service up to 9,000 feet, or a circle of about nine square miles.
ADSL makes use of three information channels--a high-speed channel for downstream server-to-client communication, a medium-speed duplex channel for upstream communication, and a third channel for conventional voice transmission, known as POTS, or plain old telephone service.
The high-bandwidth channel speeds currently ranges from 1.
One source of confusion for ADSL is that it supports two
competing modulation techniques. In Carrier-less
"People say DMT is better and will offer higher speeds--but the equipment is much more expensive, said Lev Kaye, vice president of sales for InterAccess Inc., the first ISP to offer ADSL on a subscription basis. "When we see low cost DMT equipment shipping, that's probably when will begin to implement it. But right now we are implementing CAP because it is here today."
As a standard, ADSL is still being specified. A working group
of the American National Standards Institute (ANSI) recently
approved an ADSL standard at rates up to 6.
ADSL's biggest disadvantage compared with ISDN is that it
probably won't be broadly available until at least the end of
1999--while ISDN service can now be purchased from almost
anywhere in the U.
One hotbed of ADSL activity is the city of Chicago, where, within a single week last September, an Internet service provider and a Bell company both announced plans for ADSL access. The ISP, InterAccess, is probably the world's first provider to offer ADSL as a subscription service, while the telephone company, Ameritech Corp., is launching its first field trial. Both companies are using the same ADSL supplier- -Westell Technology Inc.
Ameritech started a six-month trial last October with 200 of
its customers. InterAcess is a small ISP, and won't disclose
how many of its customers have actually signed up for ADSL
service--implying, at least, that the number is still
unimpressive. To launch the service, the company staged a face-
off pitting ADSL against ISDN and a standard 28.
InterAccess and other independent ISPs face one big obstacle:
ADSL's limited transmission length. ADSL requires that
equipment be co-located in or near every telephone central
office--which in the U.
But InterAccess still views ADSL as the best high-bandwidth solution. "We see ISDN as an interim technology," Kaye said. "It's too complex to ever become widespread--and will be reserved for the techie elite. By contrast, ADSL is so easy to implement that it can become ubiquitous. And once the connection is set up, it always there--you are always connected to your ISP. If you wanted to, you could leave your computer running when you go to work, and when you come home you would just touch the keyboard to see your all your e-mail messages waiting for you. It's not a dial up connection. You are always on."
Wireless connections via satellite
For Japan, as well as the U.
One company, Hughes Network Systems, has begun to offer Internet service via a mounted satellite dish, as well. The advantage is that you can receive broadband from virtually anywhere with an unobstructed path between the satellite and your dish. The disadvantage is that, so far, satellite connectivity is--to put it politely--difficult. Satellite connectivity requires elaborate installation, a large up-front investment of $700, and hours of tinkering to get the dish pointed precisely. Users also found that early versions of Hughes' software crashed under Windows 95, and that you must establish two Internet connections, one for receiving via the satellite, the other for sending it through a standard analog phone connection.
That was last summer. By autumn, Hughes said it had revamped its software and made the whole process easier. Most surprisingly, the company even swung a deal with CompUSA--an American computer store chain, to offer do-it-yourself kits through its 20 California stores. The kits include a 21-inch dish, 100 feet of coaxial cable, an adapter card and Windows 95 software.
Clever marketing, but this is still a very costly service. In
addition to the $700 up-front price and the time to set up the
disk, users pay $9.
So with the cost and installation hurdles, who is a good
candidate for Internet connectivity via satellite? In part,
of course, it is those people in the U.
Gaske also sees possibilities in Japan. Last April, Hughes announced an alliance with Space Communications Corporation, a unit of Mitsubishi Group, for what it called the first digital satellite service in Japan. The service is in the test stages. "Japan has very wide ISDN capability, with not much coaxial cable hookups to speak of--so there may be some unique opportunities for us," said Gaske.
>From a business perspective, satellite technology has one big
advantage over all other high-bandwidth technologies to date:
the system can expand without additional costs. And those
costs can be prohibitive. TCI, for example, the large U.
It's a tough choice to invest in infrastructure if you aren't at all certain whether you will get your money back. And so, pricing is a critical issue. "We're not only trialing the speed and convenience of ADSL, but also trying to determine what people will pay," said Ameritech spokesman Rick Aspan.
What will people pay? I don't know about you, but I'm on the Internet daily--and most of the time, I'm just interested in text. So like a lot of people, I uncheck the "load images" option on my browser so that downloads finish sooner, and most of the time, that approach works just fine. Maybe I'm a cheapskate or maybe as a writer I'm more oriented toward words. But until I see more compelling images on the Internet, I'd rather take the money I might have invested in high-bandwidth services and put it into something else. Those cross-country skis I just bought, for instance, are part of the broadest-band experience imaginable: real life.
An interview with Kim Maxwell, chairman of the ADSL Forum.
Kim Maxwell started Racal-Vadic, a major modem supplier until the early 1980s, and in 1990, he formed Amati Communications, which specializes in ADSL. He accepted the chairmanship of the ADSL Forum in 1994.
- What are ADSL's prospects in Japan?
- It's hard to say. I believe that NTT still wants to bring fiber to the home--which would deliver many gigabits, but is expensive--perhaps $600-$700 a home. But if NTT unbundles the local loop [the wiring from the telephone central office to the subscriber's telephone]--thereby giving copper pairs to alternative suppliers, then ADSL could be offered by other companies.
- Why is ISDN so costly and will ADSL be any cheaper?
- ISDN is expensive because it is a circuit-based system that requires telephone companies to upgrade the switch--even if you have a digital switch. And the software is expensive, as is the maintenance. The installation of ISDN is very complicated because of the way it was designed. There's millions of options and if you move it you have to change all the options. And it's got the same problems as ADSL in terms of transmission lengths.
- ADSL doesn't go through a switch. It comes into a central office to a concentrator, which connects to a remote ATM switch. The typical configuration in the United States, which I think will be true elsewhere, is one big ATM switch for 40 or 50 central offices. They will be connected to the central offices over a fiber link, which is already in place. Each central office will have an ATM access concentrator--a simple device.
- What does this work out to in terms of cost for the implementor?
- Under $500 a line.
- As opposed to ISDN?
- I don't know what those costs are. If the tariffs reflect real costs, ISDN is about $800 to $1,000.
- More important than cost, is the speed of implementation. An ADSL concentrator can support between 200 and 400 customers in about a two foot square footprint. An area the size of your desk will support 1000 to 1500 customers. The ADSL footprint is small. It's a completely separate network, and it's not that difficult to install. I believe that unlike ISDN, which covers 75 percent of the United States, the phone companies will have coverage for ADSL higher than that by the end of this decade.
- So you are predicting ADSL will ultimately surpass ISDN?
- No question.
- When can we expect general service?
- By 1998, you'll start seeing technical bugs worked out well enough that you'll see a major program underway for rapid distribution. The service will not be available from every central office until the end of 1999.
- Is ADSL going to be restricted to the Bell companies that have access to a central office?
- We don't know. If the FCC has its way, the phone companies would make access to copper relatively easy. In practice, it will probably vary by region. For example, Ameritech is not particularly unhappy about having non-phone company equipment on their premises, in which case it's not that difficult. If the phone company says you can have access to the wires but you can't put equipment on their precious territory, ADSL providers will have to do something more complicated, like run some copper wires from the main distribution frame over to another building.
- However, that won't be a big impediment in the long run. I believe the structure of how the phone company deals with its enemies will all be worked out.
- How do you compare with coaxial services, like TCI's @Home?
- Fundamentally, while there are some differences, the appearance to the user of a coax modem and ADSL will be virtually identical. The coax modems deliver 30Mb downstream, and have some real problems upstream. But the 30Mb is shared among all users. It's a function of how many users are on the line at one time, and what they are doing.
- Even so, will the speeds be comparable to the end user?
- In terms of raw performance, after 1Mb you won't see any difference. The truth is that if you are four miles away and I can get 1Mbps to your house, you'll be happy. If the guy next to the central office gets 9Mbps, you'll each have equal performance for quite a while because of inherent delays in the Internet. That will eventually change, assuming there are a lot of proxy servers out there and people are spitting out video--then the difference between 1 and 6 and 9 Mbps will start making a lot of sense.