SRT (Secure Reliable Transport) was initially developed by our team of IP and video experts to address the main challenges of streaming content over the internet: security and reliability.
Security is a large concern. Legacy protocols for broadcast contribution and distribution including RTMP and UDP lack built-in encryption or security mechanisms. SRT fixed this by including the industry standard AES encryption algorithm as an integral part of its software stack.
Another challenge encountered when streaming content over the internet is reliability. Though UDP is more bandwidth efficient than RTMP, (which is based on TCP) lost packets are not recovered and therefore video quality suffers. RTMP is more reliable as it can recover lost packets, but latency is greater because of its inherent congestion control. SRT greatly improves upon these protocols by including ARQ (Automatic Repeat request) error detection and correction between the sender and receiver. If the receiver does not acknowledge reception of a packet, the sender will automatically resend it.
SRT offers reliability, low latency, and content protection – and then, to top it off, we brought the streaming protocol open source in 2017. Once we made it available to the open source community on Github, it was immediately embraced as – in my opinion – the best network protocol for transferring all types of data payloads including live and file-based video.
SRT over MPLS
As developers began implementing SRT on their own hardware and software stacks, some have been demonstrating the protocol’s benefits beyond the public internet. SRT can also be used for managed networks including MPLS (Multi-Protocol Label Switching). Offered as a service by operators, MPLS is used for establishing a virtual private network (VPN) over different types of private networks and protocols. MPLS can prioritize different types of data so that low latency networks are devoted to live video streams.
With SRT’s built-in encryption, streams can add another level of security on top of MPLS for extremely valuable content such as premium sports or types of sensitive video content. Though MPLS networks are more predictable than the public internet, they can still experience fluctuations in bandwidth which can have an impact on picture quality. By applying SRT statistics, video encoders, such as the Haivision Makito series, can dynamically adapt compression levels to ensure continual streaming.
As a closed network, MPLS is more reliable and secure than the public internet, however it can be very costly. For this reason some users are deploying SRT over MPLS to ensure that they are getting the most bang for their buck.
SRT over other networks
As more companies deploy SDN (Software-Defined Networking) or SD-WANs (Software-Defined Wide Area Network) for greater network flexibility and scalability, some are also using SRT for internal live video streaming. Deploying SRT over an SD-WAN can further improve picture quality and add a further level of security in case of a network breach.
The SRT protocol can also be used for streaming content over cellular networks. When sharing live video from a remote location without broadband internet access or the possibility of leasing private network access, bonded cellular solutions for video contribution can be used along SRT to improve picture quality, latency, and ensure secure content delivery.
For remote locations without access to a fixed or mobile network, then satellite is also an option. Bidirectional satellite communications are often used for conducting remote interviews. To ensure that the interviewee is speaking to the interviewer at a natural pace, with limited delays, relying on SRT for error correction will help keep latency low, ideally under 500ms round trip, though this depends on the actual satellite and technology used.
As per the examples we’ve already covered, SRT can be applied to any IP network. Though some networks might be very predictable and less prone to jitter, streams can still be benefit from SRT’s built-in AES encryption. For satellite links where bandwidth can be extremely limited, there is little room for error when streaming, and therefore it makes sense to use SRT. For file based content, especially very large files, SRT can also be used to optimize available bandwidth even over managed networks. No matter what type of network or application, it’s worth considering SRT for delivering your content.
