The Need for Hitless Protection SwitchingPosted on September 25, 2017
Live television broadcasts are very demanding environments for signal transmission. Video signals, even compressed ones, use high-speed data flows that need to be delivered in smooth, uninterrupted video and audio streams to provide the best possible viewing and listening experiences. Signal dropouts, glitches, and other faults can be extremely distracting to audiences, so broadcasters have long been interested in technologies that can reduce or eliminate the number and intensity of signal disruptions.
All networks can occasionally experience random packet loss and multi-packet burst losses, in part due to resource contention and partly due to the many types of signals that flow between millions of sources and destinations every second. Signals sent over the airwaves or through space can experience interference from many sources, including lighting bursts and cosmic rays. Signals sent locally over copper or via long-haul fiber-optic links typically exhibit much lower error rates, but can experience occasional data losses. Data packets flowing through shared resources on public or private networks can also experience occasional congestion that causes packets to be dropped. Overall, connections using public networks can normally expect to see packet loss rates on the order of one in a thousand (0.1%). While these rates may seem low, video signals used in contribution feeds often occupy thousands of packets per second. Private networks perform significantly better, but will still be impacted by occasional random or burst packet losses every few minutes.
Forward error correction (FEC) and Automatic Repeat reQuest (ARQ) are commonly used by television broadcasters to overcome minor signal degradations. FEC works by adding extra data to the transmitted signal that can be used by the receiver to correct garbled bits and bytes. ARQ uses a communication path from the receiver back to the transmitter to signal when data blocks are missing or have been received with errors. Once the transmitter receives a lost packet indication, it will re-send the bad/missing packets.
Preventing glitches can be hard, particularly on wide area networks (WANs). While both FEC and ARQ technologies can protect against occasional missing or corrupted data, hitless protection switching was developed to specifically address short-term and long-term outages that occur on WANs. Capable of withstanding longer term outages with dozens or hundreds of consecutive lost packets hitless protection switching provides a field-proven way to reliably deliver signals across many different network topologies.
To learn more about hitless protection switching, its benefits and applications, download the white paper Broadcasters Can’t Miss with Hitless Technology.
Related Products: SMART Media Delivery Platform supports SMPTE ST 2022-7 Seamless Protection Switching.