PubNub makes the transport a non-issue by utilizing the most efficient/versatile protocol available for any given programming environment (via a client or server SDK) and providing access through a consistent and simple to use API. The SDKs are constantly updated to keep up with the latest emerging standards (such as WebSockets, WebRTC, including fallbacks where applicable) without exposing the intricacies of the protocol to developers. 

This allows developers to spend their valuable time on delivering app functionality while having the peace of mind that the app's communication backbone is delivering the necessary performance and reliability. PubNub supports many transports with fallbacks to provide safe passage beyond strict proxy authorities and firewalls.

Here are some resources with more details about PubNub's protocol agnostic approach:

If you require support for the MQTT protocol, please review How to use PubNub's scalable MQTT Interface.