Eclipse Hono

Eclipse Hono™ provides remote service interfaces for connecting large numbers of IoT devices to a back end and interacting with them in a uniform way regardless of the device communication protocol.

Connectivity is at the heart of IoT solutions. Devices (things) need to be connected to a back end component where the data and functionality of the devices is leveraged to provide some higher level business value. IoT solution developers can pick from a wide array of existing (open source) technology to implement a device connectivity & management layer for the particular type of devices at hand. While this is often fun for the developers to do, the resulting solutions are often silo applications lacking the ability to scale horizontally with the number of devices connected and the number of back end components consuming the device data and functionality.

The Eclipse IoT Working Group has therefore discussed  a more generic, cloud-based IoT platform architecture which better supports the implementation of IoT solutions without requiring developers to solve some of the recurring (technical) challenges over and over again. The diagram below provides an overview of the IoT Server Platform as discussed in the working group.

The diagram shows how devices in the field are connected to a cloud-based back end either via a Field Gateway (e.g. something like Eclipse Kura) or directly to so-called Protocol Adapters. The Protocol Adapters' responsibility is abstracting communication protocols as well as providing location transparency of devices to the other back end components. The devices upload (sensor) data to the back end while the functions/services they expose can be invoked from the back end. These two directions of information flow can be characterized as follows:

• Telemetry
  
  Data flowing downstream (left to right) from devices to the back end to a consumer like a Business Application or the Device Management component usually consists of a small set of discrete values like sensor readings or status property values. In most cases these messages are one-way only, i.e. devices sending this kind of data usually do not expect a reply from the back end.
• Command & Control
  
  Messages flowing upstream (right to left) from back end components like Business Applications often represent invocations of services or functionality provided by connected devices, e.g. instructions to download and apply a firmware update, setting configuration parameters or querying the current reading of a sensor. In most cases a reply to the sent message is expected by the back end component.

It seems reasonable to assume that the number of messages flowing upstream (Telemetry) will be orders of magnitude larger than the number of messages flowing downstream (Command & Control). The aggregated overall number of messages flowing upstream is expected to be in the range of several hundred thousand to millions per second. Note that in this architecture the same (cloud-based) infrastructure is shared by multiple solutions.

The IoT Connector component provides the central link between the device-facing Protocol Adapters, additional re-usable back end components, e.g. Device Management or Software Provisioning, and last but not least the IoT solutions leveraging the devices' data and services. Solution developers can use the IoT Connector to uniformly and transparently interact with all kinds of devices without the need for caring about the particular communication protocol(s) the devices use. Multiple solutions can use the same IoT Connector instance running in a shared cloud environment in order to share the data and functionality of all connected devices. The IoT Connector ensures that only those components can consume data and control devices that have been granted authorization by the device owner. In this regard the IoT Connector can be considered an IoT specific message broker targeted at cloud deployment scenarios.

The IoT Connector component needs to fulfill a set of non-functional requirements, in particular regarding horizontal scalability, that are specific to both the deployment environment (cloud) and the intended architectural platform characteristics (as opposed to embedding a connectivity layer into applications individually). However, these requirements are not specific to any particular application domain. From a technical point of view it makes no difference if a sensor reading received via a LWM2M protocol adapter represents a temperature or the relative humidity. In both cases the IoT Connector's responsibility is to forward the messages containing the values to (potentially multiple) authorized consumers without introducing too much latency.

Features at a glance

• Secure message dispatching
• Support for different message exchange patterns
• Used for cloud service federation
• Provides interfaces to support implementation of protocol adaptors which allow:
  • Sending telemetry data
  • Receiving device control messages (from applications/solutions)
  • Registering authorized consumers of telemetry data received from connected devices

Key words: Device Connectivity, IoT, Device Control, CoAP, AMQP, MQTT, HTTP, Data Ingestion, Kafka