ARQ

Video: 2019 What did I miss? – Introducing Reliable Internet Streaming Transport

Posted on by Russell Trafford-Jones

By far the most visited video of 2019 was the Merrick Ackermans’ review of RIST first release. RIST, the Reliable Internet Stream Transport protocol, aims to be an interoperable protocol allowing even lossy networks to be used for mission-critical broadcast contribution. Using RIST can change a bade internet link into a reliable circuit for live programme material, so it’s quite a game changer in terms of cost for links.

An increasing amount of broadcast video is travelling over the public internet which is currently enabled by SRT, Zixi and other protocols. Here, Merrick Ackermans explains the new RIST specification which aims to allow interoperable internet-based video contribution. RIST, which stands for Reliable Internet Stream Transport, ensures reliable transmission of video and other data over lossy networks. This enables broadcast-grade contribution at a much lower cost as well as a number of other benefits.

Many of the protocols which do similar are based on ARQ (Automatic Repeat-reQuest) which, as you can read on wikipedia, allows for recovery of lost data. This is the core functionality needed to bring unreliable or lossy connections into the realm of usable for broadcast contribution. Indeed, RIST is an interesting merging of technologies from around the industry. Many people use Zixi, SRT, and VideoFlow all of which can allow safe contribution of media. Safe meaning it gets to the other end intact and un-corrupted. However, if your encoder only supports Zixi and you use it to deliver to a decoder which only supports SRT, it’s not going to work out. The industry as accepted that these formats should be reconciled into a shared standard. This is RIST.

File-based workflows are mainly based on TCP (Transmission Control Protocol) although, notably, some file transfer service just as Aspera are based on UDP where packet recovery, not unlike RIST, is managed as part of the the protocol. This is unlike web sites where all data is transferred using TCP which sends an acknowledgement for each packet which arrives. Whilst this is great for ensuring files are uncorrupted, it can impact arrival times which can lead to live media being corrupted.

RIST is being created by the VSF – the Video Standards Forum – who were key in introducing VS-03 and VS-04 into the AIMS group on which SMPTE ST 2022-6 was then based. So their move now into a specification for reliable transmission of media over the internet has many anticipating great things. At the point that this talk was given the simple profile has been formed. Whist Merrick gives the details, it’s worth pointing out that this doesn’t include intrinsic encryption. It can, of course, be delivered over a separately encrypted tunnel, but an intrinsic part of SRT is the security that is provided from within the protocol.

Despite Zixi, a proprietary solution, and Haivision’s open source SRT being in competition, they are both part of the VSF working group creating RIST along with VideoFlow. This is because they see the benefit of having a widely accepted, interoperable method of exchanging media data. This can’t be achieved by any single company alone but can benefit all players in the market.

This talk remains true for the simple profile which just aims to recover packets. The main protocol, as opposed to ‘simple’, has since been released and you can hear about it in a separate video here. This protocol adds FEC, encryption and other aspects. Those who are familiar with the basics may whoosh to start there.

Speaker

Merrick Ackermans Merrick Ackermans
Chair,
VSF RIST Activity Group

Video: The next enhancement for RIST

Posted on by Russell Trafford-Jones

Continuing the look at RIST, the developing protocol which allows for reliable streaming over the internet – even in the event of packet loss, we have a look at a key feature on the roadmap.

The core proposition of RIST is to produce an interoperable protocol which brings the internet into the list of ways to contribute and distribute low-latency video. It’s resilient to packet loss due to it’s ability to re-request packets which have been lost yet is light enough for video streaming. In another talk at IBC, we learn about the latest developments which have added security and many other features to the list of capabilities.

Here, Adi Rozenberg from VideoFlow explains how this will further be extended by upcoming work to allow the source stream to reduce in bitrate in response to reduced capacity in the network. With RIST’s ARQ – the technology which requests missing packets – we find that the retransmissions can actually aggravate bitrate constrictions particularly when they are permanent. Adi proposes the only real way to solve lack of bandwidth issues is to reduce the bitrate of the source.

RIST already includes NULL packet removal so that NULL packets aren’t transmitted and are re-inserted at the remote end. This is usually a great start in reducing the bitrate of the stream. However more is needed, we need a way to tell the encoder to reduce the bandwidth of the video stream itself. This can be accomplished by RTCP.

Adi identifies the problem of identifying when extra bandwidth has returned as a reduction of bandwidth is quickly and easily signalled with retransmissions, but excess bandwidth silently returns. The system gradually increases the encoder bandwidth to always be probing the current balance of bandwidth and bitrate.

This works well when there is a single encoder and a single decoder. When there are multiple decoders, life is more difficult. The solution offered to this is to create a ladder of bitrates all of which are adaptable. Now the destination can switch between profiles. This can be extended to MPTS (Multi-Program Transport Streams) whereby, depending on the destination, services in the MPTS are dropped in order to recover bandwidth. A mechanism is used which prioritises services depending on the destination (i.e. German channels are de-prioritised on delivery to France).

The session ends with a Q&A on stream switching details and use in stat mixing.

Watch now!
Speakers

Adi Rozenberg Adi Rozenberg
CTO,
VideoFlow

Video: Panel Discussion on RIST

Posted on by Russell Trafford-Jones

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.

Watch now!
Speakers

Sergio Ammirata Sergio Ammirata
Deployments and Future Development,
DVEO
Kieran Kunhya Kieran Kunhya
Founder,
Open Broadcast Systems
Uri Avni Uri Avni
Founder,
Zixi
Mikael Wånggren Mikael Wånggren
Senior Software Engineer,
Net Insight
Ciro Noronha Ciro Noronha
Executive Vice President of Engineering,
Cobalt Digital

Video: A Study of Protocols for Low Latency Video Transport Over the Internet

Posted on by Russell Trafford-Jones

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.

Bring yourself up to date with RIST!
Watch now!

Speaker

Ciro Noronha Ciro Noronha
Director of Technology,
Cobalt Digital