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Monday, December 28, 2015 - 06:26 by Kai Hudalla
This proposal is in the Project Proposal Phase (as defined in the Eclipse Development Process) and is written to declare its intent and scope. We solicit additional participation and input from the community. Please login and add your feedback in the comments section.
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Working Group
Proposal State

The open source community has produced a lot of excellent technology, frameworks and products that help with implementing IoT applications. A developer usually selects an appropriate set of technology and components and incorporates them into an application. The chosen components need to suport the implementation of all relevant aspects of an IoT solution including device connectivity, management, monitoring, business logic and last but not least security enforcement at all levels. In an enterprise context a typical solution is about connecting a given number of homogenous devices to a particular application hosted on dedicated server infrastructure. Over time this results in a set of independent silo applications each managing their own (limited) set of devices. As of today, most of the technology created in Eclipse IoT projects specifically supports the development of IoT applications in this way.


Bosch is a major manufacturer of all kinds of electronic devices, most of which (if not all) will have connectivity built into them in the near future. Integrating these devices with individual IoT applications as descibed above has several drawbacks:

  • The repetitive implementation of common functionality like device communication and management is error prone and inefficient regarding costs, development time and runtime resources.
  • The tight integration of devices with a specific application de facto partitions the set of things into classes determined by the application the devices have been intially integrated with. This makes it hard to create new cross-domain solutions and business models leveraging devices coming from different application domains.
  • The applications implemented this way are often designed to interact with a limited number of devices in an enterprise environment only. Scaling out such applications with an increasing number of devices therefore often requires massive refactoring (if not re-architecting) of the device integration layer in order to support horizontal scalability as required in most cloud-based use cases.



Hono provides a uniform (remote) service interface that supports both the Telemetry as well as Command & Control message exchange pattern requirements. In order to do so, Hono also introduces a standard service interface for managing the identity and access restrictions.


The Hono project provides an initial set of implementations of the service interfaces described above (corresponding to the IoT Connector component in the diagram shown below in the Description section), leveraging existing messaging infrastructure components. It is not the project's intention to create an additional message broker implementation.



Hono provides a uniform (remote) service interface that supports both the Telemetry as well as Command & Control message exchange pattern requirements. 

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 upstream (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 downstream (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
Why Here?

The Eclipse IoT Working Group already serves as an incubator for projects and technology that helps with the development of IoT solutions. Hono will leverage some of this technology, in particular for the implementation of protocol adapters, while also adding missing but fundamental pieces to an open source cloud-based IoT Server Platform.


Some of the IoT Working Group's current member companies already have expressed an interest in collaborating on Hono and we have also started discussions with other prospect companies regarding their involvement in both the project as well as the IoT Working Group.


The following list includes Eclipse IoT projects that provide technology relevant for Hono:

  • leshan
  • Californium
  • Mosquitto
  • Paho
Project Scheduling

We would like to be able to demonstrate a first PoC (based mostly on the initial contribution code) at EclipseCon 2016 in Reston. A first release should be available by Q3 2016.

Future Work

As a starting point we provide an implementation based on RabbitMQ because of its easy availability both as a service in existing Cloud Foundry based environments as well as in the form of pre-built Docker images. In order to also provide an implementation supporting horizontal scale-out, we will also create an implementation based on Apache Kafka. Future versions may also support using other cloud-based offerings (e.g. Microsoft's Azure Message Bus or Amazon's Simple Queue Service).

One of the first things to change in the initial contribution will be to define and implement Hono's external messaging interface based on AMQP 1.0 for better interoperability.

Additional steps then include:

  • Support for additional device communication protocols by means of additional Protocol Adapters. In particular, we would like to support LWM2M by means of a leshan based Protocol Adapter.
  • Support for (existing) messaging infrastructure on public cloud providers.
  • Integration with (existing) security infrastructure of public cloud providers and/or IaaS/PaaS stacks.
Project Leads
Dominik Guggemos
Kai Hudalla
Interested Parties
  • Bosch Software Innovations GmbH
  • Red Hat, Inc.
  • innoQ Deutschland GmbH (Thomas Eichstädt-Engelen)
  • GE Digital
  • Siemens AG
Initial Contribution

The initial contribution will contain a ready-to-run messaging component and a Java client implementation to interact with this service.


The Java client includes the following functionality:

  • establishing a connection to a RabbitMQ broker
  • managing authorization information per topics
  • sending  messages
  • registering topic based handlers for receiving & processing messages

The messaging component includes the following functionality:

  • storing all information required for authorization
  • accepting incoming messages and
  • dispatching messages to all authorized consumers

All contributed components are structured into multiple Maven modules. The messaging service is proven to run stand alone (executable jar) or as a Docker container. The java client implementation can be used as a java library. The messaging component currently depends on RabbitMQ as the underlying message broker. Consequently, the Java client currently uses the AMQP 0.9 protocol to connect to the messaging component.


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