Multicast ABR is an interesting hybrid technique allowing multicast distribution of video streams to the home but converts into conventional point-to-point streams at a multicast gateway close to the home. Whilst the internet at large and home networks can’t be assumed to support multicast, we can use multicast for video distribution within a managed network such as that an ISP is running.
ISPs are interested in using multicast because it can drastically reduce the bandwidth in use within the network. Currently, each device watching a video requires its own feed. If with multicast, if 1000 people are watching the same stream in one local area, then that multicast gateway need only pull one version of the stream from the ISPs nationwide network. Then it can send out these 1000 individual feeds from the local headend.
Guillaume Bichot from Broadpeak explains how this would work with a multicast server that picks up the streaming files from a CDN/the internet and converts it into multicast. This then needs a gateway at the other end to convert back into multicast. The gateway can run on a set-top-box in the home, as long as multicast can be carried over the last mile to the box. Alternatively, it can be upstream at a local headend or similar.
At the beginning of the talk, we hear from BBC R&D’s Richard Bradbury who explains the current state of the work. Published as DVB Bluebook A176, this is currently written to account for live streaming, but will be extended in the future to deal with video on demand. The gateway is able to respond with a standard HTTP redirect if it becomes overloaded which seamlessly pushes the player’s request direct to the relevant CDN endpoint.
DVB also outlines how players can contact the CDN for missing data or video streams that are not provided, currently, via the gateway. Guillaume outlines which parts of the ecosystem are specified and which are not. For instance, the function of the server is explained but not how it achieves this. He then shows where all this fits into the network stack and highlights that this is protocol-agnostic as far as delivery of media. Whilst they have used DVB-DASH as their assumed target, this could as easily work with HLS or other formats.
Guillaume finishes by showing deployment examples. We see that this can work with uni-directional satellite feeds with a return channel over the internet. It can also work with multiple gateways accessible to a single consumer.
The webinar ends with questions though, during the webinar, Richard Bradbury was answering questions on the chat. DVB has provided a transcript of these questions.
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