SRT and SST Transport Protocols: Understanding the Differences

Since acquiring Aviwest earlier this year, a commonly asked question is what the differences and similarities between the Secure Reliable Transport (SRT) protocol and the Safe Streams Transport (SST) protocol are. As always, the Haivision content team is here to help provide you with the answers. Before we take a deeper dive, let’s start by explaining the fundamentals of what SRT and SST are.

SST and SRT are both real-time transport protocols designed to transport high-quality and low latency video over unmanaged networks. The fundamental difference between the two is that SRT was initially designed for wired IP networks including the internet whereas SST was developed for streaming over mobile and wireless networks.

What is SRT?

SRT is an open-source protocol used for point-to-point low latency streaming and provides secure and reliable low latency transport of live video over any IP network, even over unpredictable networks such as the public internet. Pioneered and developed by Haivision, SRT is now widely adopted and implemented by hundreds of major television broadcasters and technology vendors. Its built-in support for AES-128/256 content encryption and low latency packet loss recovery makes it ideal for remote production and contribution and is an excellent substitute for dedicated fiber and satellite. SRT is also a great alternative to RTMP since it is codec agnostic, therefore able to support 4K video and HEVC, and is continually being improved by the open-source community. Designed for interoperability SRT is also ideal for cloud-based live production workflows requiring low latency bi-directional video.

What is SST?

SST is a proprietary and award-winning network protocol originally developed by Aviwest 13 years ago when the first 3G cellular networks appeared. SST’s unique IP bonding technology can dynamically manage the quality of service to ensure reliable and broadcast-grade video transmission over 3G/4G/5G cellular, LAN, Wi-Fi, satellite, and the public internet. SST aggregates multiple network connections in real time while dynamically adapting video bitrates to meet bandwidth fluctuations. It also includes content encryption and the retransmission of lost video data. In addition to video, SST streams can also include audio, metadata, and remote control of devices such as video transmitters and PTZ cameras via the company’s DataBridge technology.

SRT and SST: Answers to Frequently Asked Questions

Will SRT replace SST?

No, SRT will not replace SST. SRT and SST are fundamentally different and complementary technologies. SST is designed for streaming over bonded mobile and other types of networks using Aviwest video transmitters. SRT was designed to reliably transport video over the internet at low latency. As an open-source protocol, it can work with any SRT-compliant hardware or software. As the two protocols serve different purposes, the two will continue to exist and work side-by-side.

Will SST be included in SRT?

There is no intention to include SST in SRT or open-source SST. SST is a proprietary technology found in our mobile video transmitters that also supports SRT for interoperability. The two protocols are designed for different use cases, some of which may require both technologies.

Do SST and SRT work together?

Yes! There are lots of use cases where SST and SRT can work together. For example, our SST receiver, StreamHub, can output video in SRT for downstream interoperability with other broadcast equipment or cloud-based live production platforms. By using both protocols, broadcasters can support a wide variety of video sources and live production workflows.

What’s the benefit of SST over 5G?

SST enables bidirectional and low latency video transmission over 5G (as well as 3G and 4G), providing a reliable connection between the field and the studio. Although the need for mobile network bonding for bandwidth aggregations may be less with 5G networks, SST can ensure reliability by automatically switching to the most reliable network. SST aggregation of 5G networks can also support high bitrate video such as 4K UHD. SST can also be used to remotely control PTZ cameras and other equipment over 5G networks.

The Latest on SRT and SST

Recently we announced that Haivision has added SRT protocol support to the PRO, AIR, and RACK series allowing for interoperability with the complete Haivision product portfolio and other SRT-enabled solutions. SRT is also supported as outputs from the StreamHub mobile video receiver. This allows our mobile transmitters and video encoders to be used alongside other Haivision broadcast technology in a wide variety of broadcast production scenarios, including multi-camera remote production, cloud contribution and distribution, and collaborative decentralized workflows.

Adding the SRT protocol alongside SST dramatically improves interoperability with live broadcast production equipment and remote production workflows that include a mix of fixed and mobile video contribution sources, especially for live sports that require both stationary and portable cameras.

“With the introduction of SRT outputs as a complement to our SST technology, we are further expanding the scope of what is possible by offering our customers the best in reliable, low-latency video transmission over any network and to a wide range of receivers, gateways, and cloud workflows,” said Ronan Poullaouec, VP Engineering Remote and Wireless Systems, Haivision.