Switched digital video

Switched video or switched digital video (SDV), sometimes referred to as switched broadcast (SWB), is a telecommunications industry term for a network scheme for distributing digital video via a cable. Switched video sends the digital video in a more efficient manner so that additional uses may be made of the freed up bandwidth. The scheme applies to digital video distribution both on typical cable TV systems using QAM channels, or on IPTV systems. Users of analog video transmitted on the cable are unaffected. See diagram to the right for an illustration of how switched video saves bandwidth on a cable company's cables in the last mile where channels are transmitted via coaxial cable.

In current HFC systems, a fiber optic network extending from the operator's head end carries all video channels out to a fiber optic node which services any number of homes ranging from 1 to 2000. From this point, all channels are sent via coaxial cable to each of the homes. Note that only a percentage of these homes are actively watching channels at a given time. Rarely are all channels being accessed by the homes in the service group.

In a switched video system, the unwatched channels do not need to be sent.

In cable TV systems in the United States, equipment in the home sends a channel request signal back to the distribution hub. If a channel is not currently being transmitted on the coaxial line, the distribution hub allocates a new QAM channel and transmits the new channel to the coaxial cable via the fiber optic node. For this to work, the equipment in the home must have two-way communication ability. Switched video uses the same mechanisms as video on demand and may be viewed as a non-ending video on demand show that any number of users may share.

Two-way communication is handled differently between cable and IPTV schemes. IPTV uses Internet communication protocols but requires an entirely new video distribution infrastructure. Cable companies in the United States elected the less costly approach of upgrading existing infrastructure, and European operators may well take the same approach. In the upgrade approach, various proprietary schemes use specific frequencies for passing messages back to the distribution hub. In the United States, there is a recent standard for two-way communications from consumer electronics devices using CableCARDs, such as digital video recorders, high-definition televisions and home theater computers known as OpenCable (or tru2way) which require three things to work:

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