Over the Top (OTT) messages are messages that flow through the data network of a mobile operator as opposed to the core network. OTT suggests something that flows ‘over the top’ of the core network. For example, a P2P SMS message travels through the core signalling infrastructure of a mobile operator, where a WhatsApp message will flow through the data connection of a mobile operator (just like any other data). In this context a WhatsApp message is regarded as an OTT message.
