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The two words get used interchangeably and they describe two different builds, with different capacity arithmetic and different demands on your access network.
THE SHORT ANSWER
Multicast IPTV sends one copy of a live channel into the network and lets the network replicate it, so capacity is set by how many channels you carry, not by how many people watch. OTT sends a separate unicast stream to every viewer, so capacity is set by how many people watch at once — but it reaches any device, works off your own network, and needs nothing special from the access network. Most operators launching a service today build OTT and shape it per subscriber in the BNG, rather than enabling multicast end to end.
| Multicast IPTV | OTT (unicast) | |
|---|---|---|
| What sets your capacity | Number of channels carried | Number of concurrent viewers |
| What the access network needs | Multicast enabled end to end, IGMP/MLD handling at every hop | Nothing special — it is ordinary subscriber traffic |
| Devices it reaches | Your set-top box on your network | Web, mobile, Android TV, Google TV |
| Works off your network | No | Yes |
| Adding a channel | Costs capacity for everyone | Costs storage and transcoding, not network |
| One more viewer | Free once the branch is carrying the channel | Costs one more stream |
| Per-subscriber policy | Hard: the traffic is shared | Straightforward: it is per-session traffic the BNG can see |
| Content protection | Conditional access tied to the set-top box | DRM and watermarking per session |
One copy of each live channel travels into the network and is replicated at each branching point; set-top boxes join and leave channel groups with IGMP or MLD. Ten thousand viewers on the same channel cost the same as one, which is why it was the right answer when everybody watched live television on a box you supplied. The price is that multicast has to work at every hop, and the service stops at the edge of your own network.
The platform packages content once and every viewer pulls their own unicast stream over HTTP. Capacity now scales with concurrency rather than channel count, but there is nothing to enable in the access network, the stream reaches any screen the app runs on, and each session can carry its own DRM and its own entitlements. This is what a subscriber already expects, because it is how everything else they watch works.
With OTT the streams cross your network as ordinary subscriber traffic, which is the useful part: the BNG can shape them inside each subscriber’s hierarchy, account for them separately, and exempt them from DDoS scoring so a popular match never looks like an attack. It does not transcode, cache or replicate video — the platform does that. How the vBNG shapes subscriber traffic.
BNGSOFT’s platform is OTT, and it is a separate platform from the XDP data plane — the BNG carries it, it does not run on it. Ingest of live feeds and VOD files, transcoding to renditions up to 4K, packaging with DRM and watermarking, a CMS with catalogue and entitlements, and delivery as unicast HTTP to apps for web, mobile, Android TV and Google TV, all under your own brand. The IPTV / OTT platform.
Concurrency is what decides the bill on an OTT build. The sizing calculator turns subscribers and busy-hour bandwidth into the packet rate and the boxes behind it.
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