RIST solves a problem by transforming unmanaged networks into reliable paths for video contribution in an interoperable way. RIST not only improves reliability through re-requesting missing packets, but also comes with a range of features and tools, not least of which is tunnelling. Cobalt Digital’s EVP of engineering, Ciro Noronha explains how the protocol works and what’s next on the roadmap.
Ciro starts with a look at the RIST Simple Profile covering the ARQ negative acknowledgement (NACK) mechanism, link bonding and seamless switching. He then moves on to examine the missing features such as content encryption, authentication, simpler firewall configurations, in-band control, high bitrates, NULL packet extraction. These features define RIST’s Main Profile.
Tunnelling and Multiplexing is a technique to combine Simple Profile flows into a bi-directional tunnel, providing simpler network and encryption configuration. Using a GRE (RFC 8086) tunnel, RIST provides a full, protocol agnostic tunnel and a UDP-only reduced overheard mode which only requires 0.6% data overhead to implement. Ciro explains a number of setups, including one where the connection is initiated by the receiver – something that the Simple Profile doesn’t allow.
Authentication and Encryption are covered next. DTLS us the UDP implementation of TLS which is the security mechanism used on secure websites. This provides security to the tunnel so everything which travels through is covered. Ciro explains the pre-shared key (PSK) mechanism in the Main Profile.
The talk finishes by covering NULL Packet removal, also known as ‘bandwidth optimisation’, header extension which extends RTP’s sequence number to allow for more in-flight packets and questions from the audience.
RIST is a streaming protocol which allows unreliable/lossy networks such as the internet to be used for critical streaming applications. Called Reliable Internet Stream Protocol, it uses a light-touch mechanism to request any data that’s lost by the network. As losses are often temporary and sporadic, the chances are that the data will get through the second or, perhaps, third time. For a more in-depth explanation of RIST, check out this talk from Merrick Ackermans
The panel here at the IBC 2019 IP Showcase give an brief definition of RIST and then examine how far they’ve got with the ‘Simple Profile’ of RIST calling out things that are yet to be done. Still on the to-do list are such things as ‘pull’ streams, encryption, simplifying the port structure and embedding control.
Fixed Key encryption comes under the microscope next asking whether there’s a practical threat in terms of finding the key but also in terms of whether there are any side-channel attacks in a ‘non-standard’ encryption. The fixed key encryption has been implemented in line with NIST protocols but, as Kieran highlights, getting enough eyes on the detail is difficult with the specification being created outside of an open forum.
The panels covers the recent interop testing which shows overall positive results and then discusses whether RIST is appropriate for uncompressed video. Already, Kieran points out, Amazon Direct Connect is available in 100s of Gb/s links and so it’s completely possible to do uncompressed to the cloud. RTP is over 20 years old and is being used for much more than ever imagined at the time. As technology develops, use of RIST will also develop.
What are the other uses for RIST? Videoconferencing is one possibility, creating a generally secure link to equipment and ingest into the cloud are the others offered.
The panel fishes by looking to the future. Asking how, for instance, the encoder could react to reduced quality of the link. How much of the all the technology needed should be standardised and what features could be added. Sergio Ammirata suggests opening up the protocol for the bandwidth estimation to be requested by any interested device.
This session, bringing together DVEO, OBS, Zixi and Net Insight finishes with questions from the audience.
Contribution via the internet is tricky but has great promise. With packet loss and jitter all over the place, how can you deliver perfect video?
Ciro Noronha from Cobalt Digital explains the two ways people get around the unreliability of the internet: FEC and retransmission. Forward Error Correction uses some maths to transmit extra data on top of the stream which allows the receiver to correct for any packet losses. This method is standard in satellite transmission where it is always used to add robustness.
Retransmission is different in that it requires a return channel. When a receiver spots a missing packet, it asks for it to be resent. Being that it has to wait for a reply, retransmission protocols like SRT, ARQ and RIST run with a configurable buffer which needs to be big enough for at least one round trip. FEC schemes also require a buffer as it needs to wait for a number of packets before it can complete the maths required.
Ciro introduces FEC and ARQ before presenting work showing experiments he’s run on both FEC and ARQ to see the limits of their signal-correcting capabilities and latency. He finishes explaining what RIST is and its status.
RIST solves a problem by transforming unmanaged networks into reliable paths for video contribution. This comes amidst increasing interest in using the public internet to contribute video and audio. This is partly because it is cheaper than dedicated data circuits, partly that the internet is increasingly accessible from many locations making it convenient, but also when feeding cloud-based streaming platforms, the internet is, by definition, part of the signal path.
Packet loss and packet delay are common on the internet and there are only two ways to compensate for them: One is to use Forward Error Correction (FEC) which will permanently increase your bandwidth by up to 25% so that your receiver can calculate which packets were missing and re-insert them. Or your receiver can ask for the packets to be sent again.
RIST joins a number of other protocols to use the re-request method of adding resilience to streams which has the benefit of only increasing the bandwidth needed when re-requests are needed.
In this talk, Ciro Noronha from Cobalt Digital, explains that RIST is an attempt to create an interoperable protocol for reliable live streaming – which works with any RTP stream. Protocols like SRT and Zixi are, to one extent or another, proprietary – although it should be noted that SRT is an open source protocol and hence should have a base-level of interoperability. RIST takes interoperability one stage further and is seeking to create a specification, the first of which is TR-06-1 also known as ‘Simple Profile’.
We then see the basics of how the protocol works and how it uses RTCP for singling. Further more RIST’s support for bonding is explored and the impact of packet reordering on stream performance.
The talk finishes with a look to what’s to come, in particular encryption, which is an important area that SRT currently offers over and above reliable transport. Watch now!
Ciro Noronha Director of Technology, Compression Systems, Cobalt Digital
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