Hitless protection switching uses two separate transmission paths to deliver identical packet streams from a source to a destination. Upon arrival, any errors in one path can be completely removed through instantaneous, transparent switching from one path to the other. Due to increasing availability of equipment that supports hitless switching, coupled with declining network costs, the technology is going mainstream allowing broadcasters to deliver ultra-reliable signals from remote venues to studios and within production and distribution networks. As compared to other error correction technologies, hitless protection switching offers several benefits, including:
- Ability to work with high-speed signals, including uncompressed HD/UHD video and 10 Gbps data flows. The simple packet-by-packet decision system avoids the computational complexity of many FEC schemes, which on depend advanced mathematical formulas that are difficult to implement for high data rates.
- Can compensate for long-term outages, such as the complete loss of one leg of the network for an extended duration. The only requirement for reliable hitless operation is for both legs to not experience failure at the same time. This is why it is important to ensure that there is no common point of failure that can affect both paths between the sender and the receiver.
- Adds insignificant amount of delay, because the packet comparison mechanism can operate on the two streams simultaneously. The only buffering needed is for the packets that arrive first on one path be buffered long enough for the packets on the other path to arrive. This buffer is therefore no worse than the worst-case delay between the sender and the receiver on the two paths, which would be needed for any type of primary/backup architecture.
- Hitless protection switching works extremely well in the fully redundant configuration that is commonly used by broadcasters. In fact, it could be considered an improvement because the “Backup” link is always on and is thus continuously monitored. Hitless protection could be considered a way to enhance the long-term reliability of a fully redundant network because it eliminates the all-too-frequent problem of an unexercised backup not being ready to take over when it is most needed.
- Able to support any RTP packet stream, whether it contains video, audio, or large data transfers. As long as the two streams are sent out with identical RTP timestamps and packet sequence numbers on each matching set of packets, a hitless receiver should be able to reconstruct a single output stream, provided the skew is within limits.
Multiple equipment and service providers have demonstrated interoperability between devices that support SMPTE ST 2022-7. As the only available technology that can withstand partial network outages lasting multiple seconds, coupled with the flexibility to support uncompressed UHD video and 10 Gbps data flows, hitless protection switching has a “can’t-miss” future in high reliability networking.
To learn more about SMPTE ST 2022-7 Seamless Protection Switching download our white paper, Broadcasters Can’t Miss with Hitless Technology.
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