Securing the signal through hybrid delivery

Delivering a rich bouquet of media services to large numbers of receivers, in all but the densest urban areas, is probably best achieved using satellite. Relatively low-cost receiving dishes can be attached to individual homes and businesses, or shared receivers can serve multi-tenanted buildings.

C-band satellites provide this delivery path reasonably well. But there is pressure to reassign the C-band spectrum to expand terrestrial cellular connectivity. This is already happening in some parts of the world, including the United States.

Ka-band and Ku-band satellites are ideally placed to take over. They offer extensive bandwidth and the downlinks are compact and inexpensive. The extended bandwidth also means they are ideal for higher resolution content, including 1080p HD and 4k Ultra HD, and extended color gamut, providing brighter, sharper, more appealing content.

The problem is that, because they are in a higher frequency part of the spectrum, transmission is more fragile and at risk of interruption. In particular, it is prone to rain fade, where the signal becomes attenuated or completely interrupted by falling heavy rain. This is a problem anywhere, but a daily occurrence in tropical areas.

Content could be delivered over the Internet, of course, but there are very severe bandwidth limitations. Because each Internet stream is a one-to-one connection, the bandwidth demands multiply to huge requirements which are simply impractical. The RFC 1112 IP Multicasting protocol does exist, but it has not been widely adopted and is not in general use.

Combining satellite with internet for failsafe delivery

The obvious solution is to rely on satellite delivery for the heavy lifting, but use Internet connectivity to fill in the gaps when rain fade and other impairments block the signal. The good news is that there is a practical and proven means of doing just this.

The first step is to move to IP delivery. This is a natural fit for the data-centric Ka-band and Ku-band platforms, and is already common. This ensures high quality delivery to a large and effectively infinitely-scalable numbers of receivers.

RIST (Reliable Internet Stream Transport) is the open specification that is widely used as the transport protocol for IP media delivery. It is designed to be robust (including both error correction and security protection) while being very efficient in bandwidth. As a transport protocol it is independent of media formats, so broadcasters can freely choose codecs and resolutions.

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What is important in this instance is that RIST is designed to support multiple delivery paths. The RIST Activity Group has used this ability to further develop a common specification for combining satellite and Internet in a single, highly robust delivery system. The full definition can be found in VSF TR-06-4 Part 7.

In a conventional satellite delivery platform the headend creates the transport streams and sends them to a modulator for uplink. Multiple receivers are the downlinks and view the signal.

In a hybrid satellite-Internet system, a processing tap is inserted between the headend and the modulator. This inserts additional metadata to identify packets within the stream. Legacy satellite receivers simply ignore this additional metadata.

The processed signal is then fed to a recovery server. In practice, this would be a distributed and load-balanced bank of servers. Geographical distribution reduces the potential load on the Internet, eliminating bandwidth constraints.

Compatible receivers display the satellite signal and viewers are happy. Should there be any disturbance, because of rain fade or other issues, then the metadata in the stream allows the receiver to identify the precise packets lost. It requests just those packets over the Internet: the inherent abilities of RIST allow them to be seamlessly inserted into the stream, and the viewer does not notice anything has happened.

The beauty of the solution is that the load on the Internet is only those packets that have been lost, so it is generally minimal and easily accommodated. The necessary buffering adds a very small amount to the latency, but is not significant to impact most practical delivery applications.

This is not a theoretical solution. It has been proven in practical implementations.

Real-world deployment

SipRadius worked with Caritech Solutions, based in Barbados, on a project to deliver high quality DTH services over Ku-band. Its geography means that Barbados has occasional but very severe rain, so consistent delivery through tropical storms was an important consideration.

Caritech had already adopted a RIST-based IP workflow from end-to-end of its operations. Together, we developed the hybrid delivery system, including a multi-transponder RIST sender infrastructure and hybrid receivers for seamless splicing.

Also included was a receiver tracking layer covering metrics for packet loss and signal quality. This enabled the creation of a real-time monitoring dashboard, tracking system health across the deployment and monitoring bandwidth demands during serious rain-fade episodes. This will ensure future network developments are matched with internet capabilities.

Its real beauty is its simplicity. The system only requests the specific RTP sequence numbers from the Internet recover server. RIST intelligent packet switching is incredibly efficient, so the viewer’s experience is of zero interruption. They never know anything happened.

As satellite broadcasters are forced away from C-band, they need a practical and proven way to guarantee user experience even on less robust satellite channels. RIST and the VSF TR-06-4 Part 7 show how hybrid satellite-IP services can be designed and implemented to deliver proven results.

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Sergio Ammirata, Ph.D., SipRadiusSergio Ammirata, Ph.D., founder and chief scientist at SipRadius and RIST Forum director, earned his Ph.D. in Physics from The Ohio State University. He developed the patented Dozer protocol, which became the foundation for the libRIST open-source library, now integral to multimedia platforms like VLC and FFmpeg. Joining the Video Services Forum (VSF) in 2018, Sergio has been a key contributor to the Reliable Internet Stream Transport (RIST) protocol, helping define industry standards for secure and reliable media transport. A recipient of the 2018 Technical Emmy Award, he continues to drive innovation in both open-source and proprietary communication technologies. At SipRadius, Sergio leads the development of cutting-edge solutions for secure, low-latency media transport, addressing the evolving needs of the broadcast and media sectors through scalable and innovative products.