What's Missing From DSL?

By David M. Piscitello
Core Competence, Inc.

In the four years since the enactment of the Telecommunications Act of 1996, DSL has firmly established itself as a broadband local access alternative. TeleChoice projects nearly 575,000 lines will have been installed when fourth quarter, 1999 results are reported ― over double the previous quarter total of 274,000.  TeleChoice speculates that over 2 million DSL lines will be installed by year-end 2000.

But is DSL access truly broadband? First, let's look at the strict definition of broadband ― you may be surprised at what you find.  Also, let's examine what you can do to improve DSL service and performance.

What Is Broadband?
In its October 1999 Notice of Proposed Rulemaking, the FCC establishes guidelines for telecom carriers who must report information about residential broadband lines in service. In the report, the FCC defines full broadband service as "information carrying capacity in excess of 200 Kbps  in both directions simultaneously."

This is more bandwidth than tens of thousands of business customers experience from Frame Relay.  It's clearly better than V.90 and ISDN.  But the canonical definition of broadband is a million bits per second or more.

DSL services offered today meet the FCC's definition of high-capacity lines (at least 200 Kbps in one direction.― in one direction). Of the DSL currently offered, SDSL-based services come closest to being bi-directionally broadband. Some ADSL users can experience downstream rates in excess of 1 Mbps, but upstream capacity is sacrificed. My ADSL service provides me 784/384 over a loop of 12,000 feet. This is terrific for Internet applications, but I don't expect to be watching full-motion color video programming or the NBA on DSL any time soon. And isn’t the end game for all broadband local access providers to deliver multi-channel, HDTV-quality programming and computing?

Are You Providing True Broadband DSL?
The typical DSL user experience, then, is not strictly speaking broadband and won't be unless the user has a truly short copper run from his or her business or residence to DSL access multiplexing (DSLAM) equipment. Today, subscribers must live or work at least within 18,000 feet of a central office (CO) provisioned to deliver full broadband service.  And, the closer, the better.

One in three U.S. residences are located within 6000 feet of a CO and they may, some day, enjoy an ADSL service of 6 Mbps or more downstream and 1.5 upstream. And if they lie within 4500 feet or closer, VDSL promises 13-52 Mbps.

But what's wrong with this picture? Do subscribers really have to play Moses and go to (or live near) the Mountain?

How To Do It
Surely not. The trick for telecom companies is to limit the length of copper over which DSL is carried literally to the last mile.  This is a matter of pushing DSL access muliplexor technology out from the CO to controlled environmental vaults (CEVs) where digital loop carrier (DLC) is already deployed.  DLC systems multiplex voice/data channels over a single link; by using DLCs in the local loop, carriers can use fewer and smaller cables to serve customers.

Several methods exist to do this.  Carriers can install xDSL line cards in a DLC; IDSL is provisioned for subscribers in this way today (well, it's at least a high capacity line).  Or, vendors can take a DSLAM and make it sturdy enough for carriers to deploy them in a CEV. Several vendors, including PulseCom and Alcatel, offer remote access multiplexors that extend ADSL services to users served by DLC systems.

However, I called this "the trick" because there is nothing simple about deploying  technology when it comes to broadband local access. While a CLEC can now ask an incumbent to install an ISDN card in a DLC to offer IDSL, the matter of unbundling facilities in controlled environmental shelters has yet to be addressed to everyone's satisfaction.

Dealing With The Incumbent
CLECs and ILECs who haven't yet reached harmony and closure on central office co-location issues must determine how to handle sharing of CEV facilities. Will a CLEC be able to lease space for its own equipment in a CEV as it does in an incumbent's central office, and how soon? Will a DSL install require both incumbent and CLEC craft to visit the CEV? How will this affect already-long install times?

The Telecom Act mandates that ILECs will share infrastructure, but since most DLCs are used to mux DS0s into DS1s, there's not a lot of infrastructure to share. Who's saddled with the expense of increasing capacity from remote terminals to central offices?   How these issues are to be resolved remains unclear.

What's missing from DSL is truly broadband local access and ubiquity. Both are within our technology reach.  However, expect recent telecom history to repeat itself. Sharing, whether it's central office space, a primary residential POTS line or a remote terminal/DLC, doesn't come easy when you are dealing with incumbent carriers.. Line sharing was a major victory for CLECs. For the sake of those CLECs who want to be around for the end game, perhaps unencumbered access to remote terminals should be the next.

David Piscitello is president of Core Competence, Inc., a network consulting firm and founder of The Internet Security Conference. He writes for CLEC-Planet from the comfort of his DSL-enabled home on Hilton Head Island, South Carolina.