I am new tot this and learning about this protocol. While reading on wiki about MQTT. the first line "MQTT is a publish-subscribe based "light weight" messaging protocol for use on top of the TCP/IP protocol."
Does this mean that MQTT only support Topic and not support or work with queue?
Because, Even I check out with available Client API (fusesource and paho). I dint found client API for Queue.
ActiveMQ supports MQTT and you can read much here :
In the last weeks the acronym of Message Queue Telemetry Transport is changed in MQ Telemetry Transport because MQTT hasn't queue concept ! :-)
As @hardillb said, publish and subscribe operations are executed on topics.
A concept of "queue" is implemented only when you use advanced "clean session" to false features that implies to broker to save messages published on a topic where a client is offline, so that when the client will return online, it will receive the messages. However, this implementation is strictly related to the broker (not necessary with a queue).
I wrote the following free ebook (focused on Microsoft techonologies) but the chapter 3 is dedicated to MQTT protocol itself.