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Understanding the RIST series of Specifications

Reliable Internet Stream Transport (RIST) is growing in popularity for contribution and distribution in the media industry, but with other similar protocols (SRT, NDI) already in use in the market, what features set RIST apart? We spoke to RIST Forum president Dr. Ciro Noronha (CTO, Cobalt), and Adi Rozenberg, RIST Forum director and CTO and Co-Founder, Alvalinks.Ltd

Dr. Ciro Noronha

What are the challenges in transporting video over IP in the media industry, and how have recent developments improved IP video transmission reliability? 
The capacity and reach of IP networks are constantly growing and more services are being deployed: gaming, cloud services, OTT services, video production, AI, and new applications. That has put pressure on the infrastructure that has to deal with sudden load and congestion. These cause packet loss, jitter issues and reroutes that are harmful for video over IP. Service providers are constantly working to improve the quality of service they provide, but this is a never-ending battle. We (as the network users) must help them and use reliable delivery solutions that are self-healing with the help of ARQ on one hand but also splitting the load over multiple paths on the other by using seamless switching. For more harsh situations an adaptive load share can be used which is similar to the techniques used by cellular bonding solutions. 

Why is reliable internet stream transport (RIST) becoming popular for contribution and distribution in the media industry, and what features make it appealing for content delivery workflows?
The RIST series of Specifications addresses the issues related to the delivery, security and future applications. The Activity Group created a clear feature roadmap in 2017 that looked at the user problems, network problems and the steps needed to address these head-on. This meant the use of the best ARQ techniques, point-to-point and point-to-multipoint applications, multicast applications in the cloud, seamless switching and bonding to address latency and adaptivity, synchronisation and simple configuration. RIST added the support of the native support for new industry standards; ST 2110, ATSC3.0, NDI and more. Security is also a top priority, and RIST adopted existing top-of-the-line techniques to address this need. 

How does RIST contribute to the progress of IP transport development and foster innovation among vendors and technical experts? 
The RIST Activity Group is composed of experts from different companies, which bring their combined experience into the design of the Specifications. RIST only defines what is necessary to ensure interoperability, thus leaving the door open for innovation.  Moreover, end users also participate in the Activity Group, and bring in real-life requirements. Recent features such as the RIST Relay came out of this work which came as a result of some users needed a solution that address security, distribution features and simplicity. 

What are the main features of RIST?
The RIST Specifications are published as open VSF Technical Recommendations, and thus freely available. The Specifications also include guidelines for implementers and users, built from field experience of vendors such as Zixi, Net Insight, VideoFlow, Alvalinks, Cobalt, Qvidum, and Nevion. This yields the best low latency ARQ, highest protection capability, tunnelling coupled with authentication and encryption, bidirectional streaming, support for enhanced delivery of any content and protocol including ST 2110, HTTP, TCP or any KVM control protocol that needs to run alongside with the media. It also includes seamless switching, bonding and link adaption to address the cases where a single link cannot provide a solution. This sets the protocol apart from other protocols such as SRT and NDI. 

Adi Rozenberg

How does RIST help mitigate outage risks and reassure high-value content owners about using IP for video transport?
One of the initial design goals for the RIST protocol was resiliency to link failures. The simple solution of switching from A to B was not good enough as every switch creates an interruption. The only way to address this is sharing resources; in this case, using multiple ISPs coupled with the simple technique of SMPTE ST 2022-7 seamless switching. This feature has been available since RIST Simple Profile; the protocol allows replication of the same stream over multiple ISPs and re-aggregation into one error free output. In addition to that, RIST recognised that some ISPs or paths may not be capable of full stream delivery. This is addressed with bonding, allowing the source to send portions of the stream over different ISPs so that they can be re-aggregated back to the original stream. To improve it further, link adaptation was added to measure the performance of each path and allow dynamic prioritisation decisions. Finally, the Specification recognised a situation where the overall bandwidth cannot sustain the stream bitrate and included the dynamic adaptation of the source bit rate to match the network condition.     

Why did the RIST AG develop a complete solution for simplifying firewall crossing for RIST streams? 
One of the big challenges for users today is the need to connect to a remote site and exchange communication about open ports, firewall negotiation and address security challenges, without involving the IT team. Standard solutions like ICE and STUN/TURN have been used by VoIP applications for many years, but they lacked features required for secure professional video applications.  Rather than retrofitting a set of disjoint existing protocols, the RIST AG elected to build a complete integrated solution based on RIST Advanced Profile, with all the security and features of that Specification.

What are the benefits of the Advanced Profile for RIST streams? 
The RIST Advanced Profile came with a forward-looking idea in mind: consider the needs of the industry 10 years from now; higher speeds, lower latency, support any type of traffic or protocol, prioritisation and classification of packets to provide faster reaction on the receiving end. Take the burden of packet recovery, switching, bonding, redundancy, authentication and encryption from the user to allow them to focus on his business. The RIST Advanced tunnel is based on RTP with embedded control plane capable of providing ARQ, performance signalling, multiplexing of flows and sub-flows created by the user, tunnel level bonding, IPv6, fragmentation and more; all protected by advanced encryption and authentication. 

What advantages does the common RIST Specification offer for vendors and users? 
The first part is interoperability; vendors work together to ensure this requirement. Next is the innovation; vendors can build new applications on top of just live delivery, for example, add control on top of the RIST tunnel, send confidence stream back, send commentator feedback, create a mesh network, create a multicast network in the cloud. Vendors can use the specification to add a competitive advantage for their applications when they see the need. Service deployment and development becomes easier, as third-party solutions can be attached to a common protocol. 

What IP challenges arise from the increasing demand for UHD video and remotely produced stadium events? 
As this type of application is moving to open networks or not requiring the use of dedicated links, the user may need to combine two or more service providers to achieve necessary internet bandwidth. For that, the protocol must provide the option to split the data delivery and, in some cases, use other providers to allow ARQ and reverse remote-control channel. These are all met by RIST Advanced Profile. Allowing remote production to be conducted through a single logical connection capable of prioritising the content delivery, providing bidirectional communication (for KVM and control) and splitting the tunnel over multiple service providers.  

How does RIST address bandwidth limitations and maintain video quality during transmission?
RIST introduced the concept bandwidth throttling with retransmissions so that ARQ will not cause additional overloads when the links are limited. Further improvements can be achieved by the use of NULL packet deletion, which saves bandwidth. This way, RIST minimises service impacts during link congestion or breakdown, maximising efficiencies with minimal bandwidth consumption. RIST also includes Source Adaptation, which can throttle the bit rate if the instantaneous network capacity becomes insufficient to carry the content.

How does RIST stand up to SRT today?
While SRT is gaining users and usage all over the world, users still need to remember that SRT is a unicast and a single connection. RIST is a superior, feature-rich professional solution. SRT is still trailing RIST capabilities (NULL packet deletion, bonding, authentication, advanced error recovery and more). For situations where the network performance is mostly OK, RIST and SRT are similar. However, for challenging network conditions, or for more advanced features, RIST is the preferred solution.