publish/subscribe protocol multiple quality of service level.. ..with at-least-once and exactly-once semantics low overhead (2 bytes at minimum) offline messaging retained messages, like a key/value store Small core, vibrant community Extreme modularity Reimplement everything in Javascript Why Node.js matters? high performance (2x at Paypal) faster application development (2x at PayPal) batteries
![MQTT and Node.js](https://cdn-ak-scissors.b.st-hatena.com/image/square/9eb601cca84a140c3c85a6dd4c289fe84ea777a3/height=288;version=1;width=512/https%3A%2F%2Fmcollina.github.io%2Fmqtt_and_nodejs%2Fimages%2Fpubsub.png)