Approaching the IoT world, one can be wondered how many protocols we can use to communicate IoT devices. There are many protocols such as AMQP, CoAP, MQTT and the omnipresence HTTP.
Trying to stay in the practical world, we can shortly compare two of them: MQTT and HTTP.
MQTT is designed as a machine-to-machine (M2M) & IoT connectivity protocol.
MQTT stands for Message Queuing Telemetry Transport.
This protocol is thus light-weight that it is often supported by some of the littlest measure and monitoring devices, and it can transmit information over way reaching sometimes intermittent networks. simple MQTT protocol architecture (broker based) for more read here