Industry Perspectives: Delivering High-Quality Video Service Over DSL Networks

VDSL2, a standard in development at the ITU-T, is emerging as an opportunity for carriers to gain a competitive advantage over cable operators by using it in the copper loop to the subscriber. Carriers can deploy VDSL today to start offering video service and upgrade to VDSL2 when they desire. While the standard for deployed VDSL calls for a spectrum allocation of up to 12MHz, it leaves a higher spectrum of 30MHz as an option. The proposed VDSL2 standard increases the spectrum allocation to 30MHz for higher performance. VDSL2 enables fiber-fast broadband at speeds of up to 100 Mbps—fast enough to deliver voice, data, and video to the widest possible audience.

VDSL2 has the bandwidth needed to compete head on with cable. Each channel of Standard Definition TV (SDTV), for example, requires 5Mbps of bandwidth with MPEG-2 compression or 1.5-3Mbps bandwidth with MPEG-4/H.264, VC1, or Microsoft WM9 compression. It makes sense, however, for carriers to upgrade now to HDTV because cable operators offer it. HDTV currently requires 12-19Mbps of bandwidth per channel with MPEG-2 compression. When the new compression technologies for HDTV become available in late 2005 or early 2006, HDTV is expected to require 6.5-8Mbps per channel.

Exploiting Cable’s Limitations
VDSL helps put carriers on a par with cable and satellite companies, giving them the bandwidth to support high-definition TV (HDTV). Raw bandwidth alone is not sufficient to ensure a high quality of video service, however. To win back market share, carriers need to differentiate themselves from their competitors by offering video with a far better quality of service and much higher bandwidth, both downstream and upstream, for data applications.

Service Differentiation Via On-Chip Service Quality Features
VDSL2 chipsets allow carriers to differentiate their services further. Breakthroughs in VDSL2 chip design provide on-chip enhancements to enforce performance guarantees on ultra high-speed services, even in extreme interference environments. Vendors of multi-service network equipment can use these VDSL2 chipsets to engineer products that provide bulletproof video service quality.

One important function is the ability to deliver multiple streams of different types of traffic to each subscriber—and to provide the best possible service to each stream. Video traffic shares bandwidth with voice and data traffic, and each service has different requirements. Video requires constant uptime and error-free delivery, since even one dropped frame can ruin a screen, and retransmitting a video frame is just not acceptable. Data transmission, like video transmission, must be error-free, but since latency is not a problem, frames with errors can be retransmitted.

Assigning priorities to voice, data, and video services—determining which gets the most bandwidth and the highest priorities—is perhaps one of the most important decisions a carrier has to make. Most carriers will probably assign the most bandwidth to video to ensure the subscriber’s viewing experience is not interrupted. If there is a great deal of noise on the line, for example, the carrier may want to reallocate bandwidth dynamically from data, which is not latency-sensitive, to video.