IoT request response protocol

Question

We need to build a server that can communicate with some embedded devices running a variant of Android. We need to be able to send commands to the device, and receive a response. A simple command might be asking the device for it's status. We won't have HTTP, so we need to have the client/device establish a connection with the server.

We were considering using MQTT as it has a lot of nice properties (QoS, lightweight, built for IoT), but it doesn't natively support a request response workflow.

We have considered building RPC on top of MQTT, but before we do I just wanted peoples thoughts on the matter. Would Websockets, WAMP, ZeroMQ be a better approach?

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Edit:

Q1: Do we even need RPC?

Q2: Is there an approach to building systems where I always send async type messages and still provide a good user experience?

Q3: Any examples?

Looking for implementation examples and hands on experience of building an IoT communication system beyond a toy example with a single device.

Answer 1

Based on your requirement of a light weight request/response protocol for IoT, CoAP (http://coap.technology/), an IETF standard, might be useful. It's light weight, and you can build RESTful services on top of it.

The other thing worth to consider is the "data model" and "service interfaces" for your server. Choosing a standard-based communication protocol, such as HTTP, MQTT, CoAP, is important, but it might be equally important to choose standard-based interoperable sensor data model and interfaces, so that your application can be interoperable and don't need to worry it becomes obsolete soon. Open Geospatial Consortium (OGC) SensorThings API (http://ogc-iot.github.io/ogc-iot-api/) might be an option to consider. It is an open standard, and it's data model is based on ISO 19156 Observation and Measurement.