DSL Prime: VDSL, ADSL Both Useful

Each technology has its role to play as broadband really begins to span the planet.

by Dave Burstein of DSL Prime and Future of TV [July 24, 2006]

Another take on ADSL versus VDSL
Decide based on the network design
Imran Hajimusa of Infineon sent this interesting take on the ADSL/VDSL question. He can be reasonably objective, because his company sells both. His comments with a few edits of mine (speeds mentioned assume real world impairments, but I'm still looking for solid data from the field):

"I have been following this issue very closely and am aware that there is lot of confusion out there. Talking to telcos around the world, I have concluded that there are 4 main scenarios and for each there is a rule of thumb that dictates the choice of technology. My company sells products in all categories, giving me some objectivity.

Internet with VoIP, mainly for underdeveloped/emerging markets. Loops are typically long and the network not that great. Rule of thumb: Go for ADSL2+, unless the consumer is looking for more. Downstream will be 5 Mbps or more for the fortunate customers nearby, a meg or less for those at 12,000 feet or more. This is the common deployment in India.

Minimum triple play, able to compete with cable and satellite, requires putting the DSLAM less than 5,000 feet from the customer, and it may be more realistic to plan for 3,000 to 4,0000 feet. That requires running fiber to outside plant. Many networks designed with pedestals within 5,000 or 6,000 feet face severe service limits and may require bonding with two lines or expensive construction. Some North American telcos are planning to bond 30 percent or more of their lines. Rule of thumb: 17 Mhz VDSL2 is the right solution, with best speeds of 40 to 50 Mbps down, and up to 5 Mbps up. Several major telcos are currently deploying.

VDSL2 beyond 6,000 feet is just a desperate attempt which will not pay off with a performance increase. To utilize VDSL2 capability you have to push fiber deeper and forklift the remote terminal close to home. VDSL on longer loops is like driving a Ferrari on crowded Los Angeles freeways instead of German high speed Autobahns. You pay a lot, but you do not really enjoy the ride. Rule of thumb: Go for ADSL2+ or upgrade your network and go for VDSL .

Triple play with fiber to the curb or basement. Common in Japan and Korea, coming to Germany, Paris, Holland, Toronto, and New York. Speeds offered range from 50 down/10 up to 100 meg in both directions. Loop length < 2,000 feet and for highest speeds less than 600 feet. Rule of thumb: For short loops, VDSL2 at 30 Mhz.

New builds. Fiber is cheaper than udon noodles. Randall Stevenson of AT&T said in 2004, "All new deployments will be fiber." It's taking a little longer, but with speeds now over 100 meg and equipment costs down to about $200, virtually every carrier believes in fiber. Rule of thumb: Fiber at 100 Mbps or more. North America's large carriers are choosing GPON, Asia mostly the less expensive GEPON, and Europe mostly GPON with some active Ethernet.

This seems sensible to me, with one disagreement. When a pedestal or exchange is 6,000 feet from some homes, inevitably others are closer and even within a thousand feet. So I'd consider using full rate VDSL, to allow some if not all customers to get higher speeds.

As noted last issue, however, VDSL may only be slightly more expensive but also requires more space and power. Some telcos believe they need standard services for all customers, and don't want to sell 70 Mbps to some if only a few can get that speed. Others are happy to sell "up to" speeds, which need careful promotion to avoid deceiving and angering customers.

Saying "the network design determines the right chip" also begs the question of "what's the right network design?" Whether to go fiber all the way (Verizon,) close (Korea Telecom) or 5,000 feet (Telstra, AT&T, Bell Canada) remains a crucial debate.

Copyright 2006 Dave Burstein.
The DSL Prime Newsletter is reprinted with permission.

"The power of the printing press belongs solely to those who own the presses"
—A.J. Leibling

The Internet is the cheapest printing press ever invented.