With the start of a new millennium, it seems anatural time to discuss the coming generation of computer telephony products and how they will affect the way we communicate and do business.
By now, readers of this magazine should be familiar with voice-over-IP and related products. Last year, the magazine ran numerous articles and product reviews (and several of my tutorial columns) that described how voice-over technology works, how those products perform, and why businesses want them. Somewhat quietly, several new companies have been
working on a new kind of voice-over-xx technology that promises to reduce communication costs for businesses as well as residential customers. That technology is voice-over-DSL.
DSL stands for digital subscriber line and refers to a group of standards that allows for high speed data transfer over normal copper twisted pair telephone lines. The driving force behind the development of DSL was to provide residences and small businesses with a high-bandwidth digital
connection to their Internet service provider (ISP). DSL costs much less to install and operate than a T-1 circuit. Asymmetric DSL, or ADSL for short, is the most commonly available version of DSL and has the potential to provide downlink speeds of up to 7 Mbps with uplink speeds of up to 1 Mbps. Thats high speed, dudes and dudettes. While much of residential ADSL today is limited to download speeds of 680 Kbps, thats still more than an order of magnitude greater than the typical 48 Kbps
throughput that a typical 56k modem can muster.
DSL downsides: While still a relatively new offering, some telcos have been slow in rolling out the service, so it may not be available in your area. Also, because analog twisted-pair wires were not designed for transmitting high-speed digital signals, subscribers must usually be within three miles of their central office. Beyond this distance limit, the DSL signals rapidly degenerate and become unusable (after all, multi-megahertz DSL signals are traveling on
plain old unshielded twisted-pair cable designed for 3 kHz bandwidth speech!). This means that today, up to 50% of households and businesses cannot order DSL. But even with these limitations, many
order and use DSL. And with competitive local exchange carriers (CLECs) and ISPs getting into the game as of late, DSL should be gradually easier to get for those who are currently left out. By the way, if you want to check your phone number and see if DSL is available, check out this handy on-line
Voice-over-DSL technology enables the multiplexing of up to 16 voice lines plus a high speed Internet access port onto a single DSL line. Thats right:
Over a single twisted-pair line
. For VoDSL to work, a special gateway device must be installed on both sides of the DSL line. The central switching facility (central office, or CO for short) hosts a high-density DSL gateway device that receives
the ATM or frame-formatted DSL data stream and de-multiplexes the voice channels directly into the Class 5 switch. The data channel is handled directly by the ISP facility via the regional packet network. An integrated access device (IAD) is needed at the customer site, too this is about the size of an external modem and provides the voice line connections and Ethernet data port. One of the distinct advantages of the VoDSL-derived data port as compared to a modem is that it is always on,
and as such, does not invoke a dialup delay when access is desired.
There is one intrinsic downside to VoDSL. As more voice circuits become busy for a given VoDSL line, the speed of the Internet connection gets progressively lower. For some businesses with high voice and data traffic profiles, this may not be acceptable. Proponents of VoDSL counter by saying that Internet access would not often degrade below 128 Kbps, still over twice as fast as a 56k modem.
Plain DSL service costs about $50/month
plus a setup fee. Service providers of VoDSL would then charge fees for voice and data connectivity that would make the cost per line a bargain for users as compared to conventional access fees. Since businesses pay more for phone lines than residences, and since the primary reason for VoDSL is cost savings, these products have a better starting chance of making it with small- to mid-sized businesses. However, there is an increasing trend for upscale residences to install two, three or even four
phone lines. For them, VoDSL connectivity should look attractive too, if it results in significant savings over conventional phone line and Internet connectivity costs. Both businesses and residences are targets for VoDSL vendors. The stated goal of VoDSL providers is to have a competitive offering for customers who spend at least $150 a month on voice and data services.
The groundbreaking vendors who are building VoDSL equipment include
Clara, CA 408-567-9277),
(Santa Clara, CA 408-585-2100), and
(Los Gatos, CA 408-399-1300). These are well-funded groups on a serious mission to lower connectivity costs. Follow their progress and you are essentially tracking this emerging industry segment.
Will it fly?
To say for sure if VoDSL will be a hit or not requires a close look at the
technical and market factors, both pro and con. Then you have to make some educated guesses about the market forces that will result when these boxes start hitting the street this year. VoDSL is very cool technology, but its not easy to know if it will find a comfortable spot in the telecom marketplace.
One question that will be on the minds of prospective VoDSL consumers: Will VoDSL voice circuits be as reliable as phone service today? If vendors deploy buggy systems at early customer sites, it
could damage consumer confidence in the technology and greatly slow or kill any chance for market penetration. With the pressure of the VoDSL vendors to deliver their solutions and begin capturing market share, this is a very real risk. Bottom line: We users of telephones have a
low tolerance for telephone service downtime. There are precious few conditions that justify a loss of dial tone. When VoDSL goes in, it had better be fully tested and ready.
DSL availability also needs to continue to
grow for VoDSL to take hold. Only 75,000 DSL subscribers existed nationwide as of mid-1999. This is not exactly a groundswell of support for DSL more like a drop in a very large bucket of lines. Pacific Bell alone services more than 18 million phone lines. If the telcos, CLECS, and ISPs all enthusiastically get into the VoDSL game, I think there is a good chance for VoDSL itself to actually drive stronger DSL penetration and growth.