Hitchhiker's Guide to Streaming Media: Multicast

It is worth highlighting that most true IPTV networks use multicast. They usually all use a single network provider to deliver the service to the end users, and provide a fixed customer premises equipment (CPE) device, also known as a set-top-box. This positions many regional ISPs well to become IPTV players, and also helps to differentiate between IPTV and internet TV services.

It is also worth pointing out that so-called “live peer-to-peer” networks are often based on early implementations of application layer multicast. They are highly erratic and have poor performance metrics and no network layer control. Additionally, because many networks are DSL-based (assymetrical), they require a higher (two or more) number of upstream routers to provide a single downstream link. They actually make the network less efficient.

By contrast, IP multicast at the network layer splits copies and replicates packets automatically on the wire they are sent down and with little or no overhead on the router; in fact, in any case where there are two or more users on a router for the same stream the network efficiency is effectively massively increased.

Admittedly this is all only relevant to live or linear content. Video-on-demand is clearly a personal 1:1 experience, so multicast doesn”t directly benefit end users of VOD content. However, note that edge-caching CDN systems that use multicast to update their caches can be many times more efficient than without since all nodes can be updated in parallel. Similarly, P2P for VoD can provide an increase in efficiency, and this type of approach is being seen in catch-up TV services currently appearing in the market. Network Multicast would improve these and additionally allow a quality of service to be introduced for time to deliver content – something not possible with application layer techniques. It is likely that set-top boxes with caching facilities will, over time, be expected to be pre-cached using multicast delivery for efficiency at scale.

Despite the inapplicability to VOD in general, with the huge growth of internet radio and with internet TV hot on radio’s tails, as well as more and more demand for live events, multiplayer gaming, and also finance and software markets requiring the same data to be delivered to many places quickly and cheaply, multicast is a very useful and growingly popular technology offering better services with dramatically lower cost. Although it has taken a long time to mature, the internet is steadily becoming multicast-enabled.

Which is, quite literally, music to everyone”s ears.

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