Page 21 - EngineerIT September 2022

ICT VIDEO STREAMING

Video buffering smooth experience. But video streaming buffering is not new so the question is: why

Spare a thought for our (mobile) are those alleviation mechanisms not working very well?
network operators. Infrastructure
upgrades are planned as multi-year Real-time internet protocols
projects and are based on expected Data is transferred across the internet using protocols of datagram exchange. The
growth of data (and other) usage base protocol is UDP (user datagram protocol), where the data is divided into packets
and the ARPU (average revenue per of typically a few kilobytes and transferred one after another from source address
user). Who knew COVID-19 would through one router to the next until it reaches the destination address. The transfer
hit? Certainly, it was not planned for. time is typically in the 2 -15 millisecond (ms) range. It is a ‘best effort’ protocol where
A typical video stream operates at packets may be discarded or incur errors to the bytes on its way to the destination.
between 2-6Mbits/s and consumes The most used protocol is TCP (transmission control protocol) that sits ‘on top of’ UDP
an average of 1GByte per hour of where for each inter-router transfer, the packets are re-sent until they are received
data. Going from a few hundreds of error free (or time out and give up). The retry process incurs further delays and the
thousands of these to tens of millions transfer can be in the order of a few hundreds of milliseconds. It is worth noting that for
within a six month period is a steep ask video conferencing applications, a round-trip delay of approximately 350ms becomes
of our operators, particularly for live noticeable to a human observer.
event streaming where the data to each Video conferencing applications were the first demand to retrofit the datagram
consumer is simultaneous. transfer protocols for live media applications, resulting in the development of RTSP
Internet data traffic is passed from (real-time streaming protocol), RTP (real-time transport protocol) and RTCP (RTP
a source internet protocol (IP) address control protocol) carried over either UDP and/or TCP. These are very effective for low
to a destination IP address through a delay communications and have served the industry well to date. It is a ‘push’ based
collection of routers joined together approach where a client requests a streaming session from the server (RTSP) and the
by fibre/wires/wireless ‘pipes’. The server then ‘pushes’ the media data packets (RTP) to the client. The client indicates to
negotiation of the data exchanges the server how well the session is going through RTCP, allowing the server to react to
uses predefined international standard connection conditions by increasing or decreasing the data packet rate to the client to
protocols. Both the routers and the give a smooth and unbroken experience. The server does most of the work as every
inter-connecting pipes have capacity client session is unique, even if all clients are viewing the same stream.
limitations to how much traffic they can Initially these protocols (or derivatives thereof) were also used for the growing
handle all at once. For fibre connections, demand for live radio/TV, video-on-demand (VOD) and podcasting applications, where
the router capacity is typically the the challenge is a one-to-many mechanism where ‘many’ means millions all at the
limitation and vice-versa for the older same time. It became apparent that the limitations of the RTSP family of protocols
mobile 2.5G connections. Everybody was its inability to scale from serving a few thousand to millions of simultaneous client
shares the resources equitably without sessions. This is primarily related to the ‘push’ work that the server needs to do and
distinction between browsing a website therefore requires specialised servers. The use of HTTP (hyper-text transport protocol)
or streaming a video session. When the comes in here. It is a file-based protocol for streaming applications because of its ability
capacity of a link is reached, the data is to scale. However, it does not come without its own limitations in media streaming
buffered or queued for everyone using applications. n
that resource. For a website or a simple
file download it takes a bit longer than In Part 2 the author will discuss HTTP streaming and its limitations.
usual but this is not usually annoying. A
video stream, on the other hand, stalls About the author
at the destination and even for short “Dr Keith L Ferguson, Chief Engineer, Nexgen
periods of a few seconds, still irritates Enterprises and Institutions, CSIR. Dr Keith
the viewer. Only one element, router or Ferguson received a PhD in electronic
pipe in the link needs to reach capacity engineering from the University of Manchester
before all users downstream on that link Institute of Science and Technology in the UK.
experience buffering. Consequently, the He has more than 30 years experience in video
buffering seen in your session may have and image processing including the design
nothing to do with you, but someone of novel encoding techniques for content
else whose independent session is distribution systems and the associated
influencing your link. streaming protocols. Keith has supervised post
The flood of demand for internet graduate students, published academic papers,
video services in these recent times spun out a technology company in the UK and
causes the capacity limits of the holds multiple international patents.”
network links to be reached more
frequently, giving you a less-than-

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