Very-high data rate DSL (VDSL
), sometimes also called
very-high bit-rate DSL
, is exactly
that—a high-bandwidth variant of DSL. Most implementations are capable of downstream
bandwidths in excess of 50Mbps. Consider for a moment that most VDSL deployments are in
residential settings and that the service provides in essence a DS-3 worth of capacity, and you
begin to appreciate the “very-high” aspects indeed.
There are a few installations of VDSL available in large markets, including Denver and Phoenix
in the United States. These services leverage VDSL to provide video, data, and voice services over
the DSL circuit. With over 50Mbps, it’s possible to provide four broadcast-quality video streams
over the connection, while also supporting an always-available Internet data path and analog
voice services—a road to the fully converged network if you will.
Of course, you can’t get something for nothing, and VDSL is no exception. The significant
downside to the technology is its limited range. Stated another way, ADSL technologies can frequently
extend to over 18,000 feet, whereas VDSL is limited to 4,500 feet. The highest data
rates are attainable at only 1,000 feet in most real-world settings.
The DSL types described in this chapter are summarized in Table 27.1.