Industry Perspectives: Delivering High-Quality Video Service Over DSL Networks
Latency, Bearer Channels Critical to Video Service Quality
To maintain a high quality of video service, carriers have to separate each type of traffic and treat it appropriately. Two concepts are key here: latency and bearer channels. Low latency is required for voice, while data and video can tolerate higher latency, since error-free transmission is more important. Reed-Solomon Forward Error Correction, along with a DSP technique called interleaving, provides protection against impulse noise on paths which can tolerate higher latency. Impulse noise, caused by natural causes such as lightning, can temporarily interrupt transmission, and therefore, disrupt services. A voice path that requires minimal error correction and low end-to-end latency may not use interleaving and, therefore, can be separate from the video and data traffic path.
In addition, video over DSL offerings require a way to separate channels logically, so that in a home with two or three TV sets, each can be tuned to a different channel. The latest VDSL chipsets enable logical separation by using bearer channels, each of which can be assigned to a different TV set in the household.
Additional features enhance video service quality. Seamless Rate Adaptation minimizes disruptions to services by automatically maximizing the available bandwidth on the line in the presence of changing noise profiles. Another feature, Dynamic Rate Repartitioning, enables carriers to re-allocate bandwidth automatically between bearer channels or latency paths, thus ensuring the best video, Internet, and voice service quality. Mom, Dad, and Junior may each be watching different TV channels, while big sister is accessing the Internet to research a paper she has to write. When Mom shuts off her TV, that frequency can be allocated to Internet access to boost the data rate.
Dynamic Rate Re-partitioning also enables carriers to offer value-added, data-rate-on-demand services. A subscriber with a 2Mbps service who needs to participate in a full-duplex, videoconference, which requires 6Mbps, could book the extra bandwidth with the carrier. The carrier can add the bandwidth dynamically, ensure quality of service, and charge the subscriber an additional fee for the service.
Factors for Success Are in Place
Carriers finally have everything they need to offer a superior video service that will attract new subscribers—a hybrid network strategy that provides fiber-like speeds to the home, without the fiber; a single high-bandwidth standard for copper (VDSL2); and quality of service technologies embedded at the chip level. High-quality video service, as well as new, interactive digital TV models that cable cannot match, will give carriers new revenue streams and provide a migration path to other high-bandwidth services.