Combining Satellite and IP for Resilient Media Delivery at Scale
The ability to send broadcast content over the Internet has undoubtedly provided the broadcast industry with a cost effective, efficient and flexible means to transport video content. However, while IP is a great alternative to traditional distribution methods for certain use cases such as contribution and remote production, it’s less effective at sending the same content to lots of different places concurrently, as may be required when distributing live and sports events to affiliates or for primary distribution. Factors such as bandwidth variability and network congestion make it difficult to achieve the desired resilience, at scale. Consequently, with its wide reach, satellite distribution remains the best way to send the same content to lots of receivers at different locations around the globe.
The Five Nines Challenge
While satellite technology is great at doing the heavy lifting of sending content to multiple receivers in these scenarios, there’s always a possibility that in some areas, the satellite signal could be subject to interference whether from rain fade or other external factors. If this happens, the quality of the broadcast can be degraded or in the worst-case scenario, the feed could be lost completely, both of which impact revenue. Satellite C-Band is not subject to rain fade, but in many places of the world, this set of frequencies is being re-allocated to cellular networks. Satellite Ku-Band has plenty of bandwidth, but due to the shorter wavelength, it is very susceptible to rain fade. As C-Band becomes less available (and may disappear altogether as an option), something needs to be done to move the services to Ku-Band.
Broadcasters today strive to deliver five nines uptime, meaning 99.999% reliability which equates to around 5.26 minutes of downtime per year. Obviously, achieving this level of availability is no easy task, so any interruptions to satellite transmission need to be mitigated. One potential way to prevent potential signal degradation or downtime when employing satellite distribution as the primary distribution method is to use the Internet to recover any lost data and fill in the gaps. We call this satellite and IP hybrid distribution.
The Case for Hybrid Distribution
When content is transmitted in compressed streams, every packet counts. Every lost packet is a glitch, and in distribution, this isn’t acceptable. To get the quality that viewers expect, and that content owners, rights owners and broadcasters require, one way or another, every packet has to be delivered.
With satellite and IP hybrid distribution, satellite is used for primary distribution, and the Internet is used for error recovery, to pick up any lost packets, and deliver them to the locations where they are needed. In this set up, satellite provides the much-needed scale, and the Internet provides the required resilience.
The RIST (Reliable Internet Stream Transport) specification has recently been enhanced to fulfil this need by enabling satellite to be used as the main distribution channel, with RIST as a backup to recover lost data. For anyone not yet familiar with RIST, it’s a set of open-source, interoperable protocols for transmission of content over the Internet with low latency and security.
RIST’s latest development, the RIST Satellite-Hybrid In-Band Method (VSF TR-06-4 Part 7), offers a way to combine satellite and IP to create an efficient and robust content delivery model. By using the satellite as the primary distribution channel, with RIST to recover any lost or corrupted data, broadcasters can leverage satellite for reach and scale, while also gaining the resilience that IP offers. While this approach is useful for any media companies sending content via satellite, it’s particularly relevant for Ku-band satellite transmissions, which are highly susceptible to rain fade.
Easing the Transition
One of the requirements of this hybrid method is that media companies and broadcasters need to be able to roll it out gradually. When sending out the same content to multiple receivers, some takers may be upgraded to the hybrid method, and others not. As a result, one of the key requirements is that it is backward compatible with existing satellite delivery systems.
The RIST in-band method works by adding a small amount of data into the transmission before it is uplinked to the satellite. This way, the upgraded locations can use this information to detect lost packets and then request that missing data be resent over the Internet using RIST. Locations not using this method will simply ignore the inserted data. It's very bandwidth efficient, both in the satellite segment, and in the terrestrial segment, and being backward compatible, can be gradually rolled out. Additionally, for locations that do not need the full complement of programs in the feed, VSF TR-06-4 Part 6 can be used to further optimize the bandwidth usage by only resending components of the desired programs.
Ongoing Development
The RIST activity group continually works to enhance and further develop RIST specifications to include additional features. Following on from the in-band method recently developed and discussed in this blog where information is inserted into the transmission before it is uplinked to the satellite, the RIST activity group is now working on alternative methods, one of these being the out-band method where there is no need to insert information into the transmission. Additionally, the RIST activity group is also developing a technical recommendation to meet the needs of users when there is already an IP link over satellite or other RF distribution channels, such as Over-The-Air (OTA) television feeds. Watch this space for these further developments.
For more information about RIST-enabled products, and to find out how the RIST Satellite-Hybrid: In Band Method can benefit your operation, get in touch.