The Taxonomy of OTT Video
As you can see, the definition of OTT really depends on where the service is charged, rather than on any specific technical strategy.
While Netflix and YouTube are often cited as typical OTT services, they actually represent only one type: “Pureplay OTT” for the purposes of this article, to distinguish them from the more tightly workflow-integrated broadcast OTT models discussed above.
Going further, we could loosely group the different models like this:
Digital Terrestrial Television (DTT)/Direct to Home (DTH)
The operators may use a DTT or DTH system to provide traditional broadcast services. They may or may not use IP on these privately managed networks, and will require specific consumer devices/ Set-Top Boxes to connect to these networks. The OTT application control (MHEG/ EPG data, etc.) needs to be transmitted over the (usually non-IP) broadcast network as part of the broadcast transmission. (The red button trigger is sent in the broadcast stream.)