The future of copper: rumors of DSL’s obsolescence appear to be premature
If you believe some pundits and industry observers, widespread deployment of FTTH (fiber to the home) is just around the corner. Some also suggest that recent FCC decisions deregulating new FTTH deployments as well as falling equipment and installation costs are pushing fiber deployment over the tipping point.
Because full fiber loops can carry data at speeds of 100 Mbps, companies can easily provide voice, data and video services over a single line. Controlling this fat pipe would allow the Bell companies to offer complete service bundles to match anything offered by the cable providers. However, there remain substantial barriers to major fiber deployment that suggest copper will remain the industry’s workhorse for many years to come.
Cost continues to be the single biggest obstacle to widespread fiber deployment. The CIMI Corporation consulting firm estimates that infrastructure costs for FTTP (fiber to the premises) are about five times as much as DSL in the best case scenario. Current estimates find that FTTP deployment costs are between $150 and $200 per linear foot (including trenching and additional costs such as insurance), depending on the region and population density where deployed.
The Bell companies also have significantly reduced their capex (capital expenditures) funding. Traditionally, access line growth has been the principal driver of capex. However, with access line numbers falling, there has been less money available for network investment. RBOC capital expenditures have been steadily falling since peaking in the year 2000.
Finally, the Bells currently have in place nearly twice the copper they need for current working lines. Largescale replacement projects would trap a tremendous amount of capital in investments that might take years to pay off. These investments can be difficult to justify in the face of declining access line numbers. New deployments of fiber might make sense where there is a need to refurbish or augment the current plant, but where a glut of copper remains, it is difficult to justify the stranding of such a useful asset.
Relying on historical census data to predict future deployment, the optical fiber developer OFS completed a forecast of likely FTTH deployments in the next 10 years. The company forecast just over 20 million FTTH subscribers by 2010. Even in this optimistic scenario, the total would equal only about one-tenth of the phone customers nationwide.
The Evolution of Copper
Most industry watchers are familiar with the mechanics of DSL technology. DSL uses more bandwidth than an analog voice call, making use of frequencies transmitted above 4 KHz. For traditional residential ADSL service, more bandwidth is used for sending information downstream to the user, with fewer channels reserved for sending data upstream. Thus, ADSL transfer rates are faster downstream–perfect for web surfing and similar asymmetric applications.
When these signals reach the CO, the data they represent are aggregated by a DSLAM (DSL access multiplexer), thousands of which are deployed in COs across the country to connect customers to high-speed networks.
DSL is, however, a distance-sensitive technology. The further the user is from a CO, the more degraded the signal becomes and the slower the transfer rate. The extreme distance limit for ADSL service is 18,000 feet, and download speeds up to 8 Mbps are only available to a distance of about 6000 feet. Upstream speeds are typically between 128 kbps and 640 kbps.
One perception of DSL is that it’s a mature technology facing near-term obsolescence. Nothing could be further from the truth. Creative companies have continued finding new ways to exploit the decades-old legacy copper network. Technologies that will be commercially available within the next year or two will allow data transfer at speeds exceeding 50 Mbps, fast enough for even the most bandwidth-intensive applications.
Companies could use copper to transmit not just voice and data, but also full-motion video over multiple high-definition television channels. These future varieties of DSL promise to surpass current high-speed connections by offering download speeds 30 times higher than what is now commonly available. The following DSL types are either currently in service or will be commercially deployed within the next 12 months (see Table 1):
* IDSL (ISDN DSL) allows symmetric downstream and upstream transfer rates of 144 kbps. The primary advantage of this technology is that it can be provided to customers who are located far from COs.
* ADSL (asymmetric DSL) is what most people refer to as DSL. ADSL is a consumer-class service that allows downloads at speeds up to 8.0 Mbps if the customer is within 6000 feet of a CO. Typically, however, maximum ADSL download speeds are sold and capped at 1.5 Mbps.
* SDSL (symmetric DSL) is a business-class service providing equal upstream and downstream transfer speeds. Unlike ADSL, SDSL requires a second loop separate from the customer’s voice service.
* SHDSL (symmetric high-speed DSL) is another business-class service, which allows equal downstream and upstream speeds of 2.0 Mbps to a range of 18,000 feet.
* VDSL (very high-speed DSL) provides an extraordinarily fast connection over standard copper wiring. It will be best suited to urban areas or other areas close to the DSLAM, because it only operates at high speeds to a range of about 4000 to 5000 feet. VDSL can be used to provide simultaneous voice and Internet service as well as multiple channels of high-definition video. VDSL can be deployed over the existing copper network.
* ADSL2 and ADSL2+ are two newer varieties of ADSL offering substantially faster transfer speeds with greater distance flexibility than VDSL. On short loops (fewer than 5000 feet in length) downstream transfer speeds can be up to 12 Mbps for ADSL2 and 25 Mbps for ADSL2+. On longer loops, these systems will revert to the same capabilities available with today’s ADSL. This flexibility over both short and long loops means there will be substantial cost savings for deploying ADSL2 or ADSL2+ instead of VDSL for most applications. These technologies may therefore be more widely deployed.
Standardized VDSL hardware is now available. Deployment could begin within the next 12 months if a satisfactory business case can be made. ADSL2 is also available now, although not used for the bulk of existing customers. Early ADSL2+ hardware is available from some vendors and will likely be commercially deployed within a year.
Industry disagreements over VDSL technical standards have delayed that technology’s availability. During this delay, ADSL technology has rapidly improved to the point that the ADSL2 and ADSL2+ varieties may have become a more cost-effective means of deploying a similar very high-speed broadband service.
Lost in much of the discussion over future fiber deployments is the fact that as of last fall there were only 64,700 FTTH subscribers in the entire United States, with the large majority of those served by city/municipal networks or small independent companies, not the large ILEC monopolies (as reported by market research firm Render, Vanderslice & Associates).
Nearly all homes and small businesses in the United States are still connected to the nationwide phone network by the same pair of twisted copper wires that have been in use for decades. Given the continued hurdles to fiber deployment and the increasingly fast transmission speeds available over the existing copper network, it is likely that copper will continue to be the industry’s workhorse for many years to come.
Table 1 DSL characteristics.
Type Max Rate Max Rate Max Reach
IDSL 144 kbps 144 kbps Extendable via
ADSL 8.0 Mbps 1.0 Mbps 18,000 ft
SDSL 1.5-2.0 Mbps 1.5-2.0 Mbps 18,000 ft
SHDSL 2.0 Mbps 2.0 Mbps 18,000 ft
VDSL 52 Mbps 1.5 Mbps 4000-5000 ft *
or or or
13 Mbps 12 Mbps 2000-3000 ft *
ADSL2 12 Mbps 1 Mbps 18,000 ft
ADSL2+ 25 Mbps 3 Mbps 18,000/5000 ft *
Type Applications Availability
IDSL Low-cost, Current
ADSL Consumer-class Internet Current
SDSL Business-class access Current
SHDSL Business-class access Current
VDSL Consumer-class full-service Within 12 months
access network (FSAN) for
voice, video & data
ADSL2 Consumer-class Current
ADSL2+ Consumer-class Within 6+ months
* VDSL and ADSL2+ have maximum ranges equal to current ADSL, but past
5000 feet their maximum achievable speeds are dramatically reduced.
Ron Marquardt is technical director, strategic development at Covad Communications (email@example.com).
COPYRIGHT 2004 Horizon House Publications, Inc.
COPYRIGHT 2004 Gale Group