Small footprint network middleware designed to connect any IIoT device
04 October 2018
Nick Pridham, Managing Director of middle experts Hamersham, outlines the benefits of using DDS data exchange technology to enable swift and secure peer-to-peer communication in a wide range of embedded applications.
What is DDS?
DDS provides a way for devices to exchange data on local or remote networks. It is a small footprint network stack that consumes minimal resources and can be deployed on any device. Small embedded sensors running on machines in the field, or cloud servers running in data centres, can all run DDS. DDS will take care of data exchange between any of these devices.
How does DDS work?
DDS works on the publish/subscribe principle. This means data exchange is peer to peer and does not need a message broker or central server. A device with data to offer to a network (publisher) is matched with a device which has a requirement to receive this data (subscriber). Matching is done via Data TOPICS and a discovery process. A Data TOPIC could be a package of machine health information such as temperatures, speeds, working hours and fault codes. This Data TOPIC could be required by a neighbouring device of the same type, a data logger, a cloud server, a PLC controller and/or a measuring diagnostic tool.
In other words, any DDS device can exchange data with any other DDS device. Data can be exchanged between publishers and subscribers via unicast, multicast or broadcast meaning data from one device can easily reach thousands of other devices.
Why would I use DDS?
DDS saves engineering time and money by automating data exchange between devices. As networks grow to thousands of devices, network configuration and management can be cumbersome.
If each new device added to a network needs configuring with IP addresses and port numbers then this can consume large amounts of engineering time.
DDS takes care of this in the background and makes sure network participants can exchange data on the basis of TOPICs.
DDS therefore allows networks to scale automatically. Thousands of devices can join a network auto configure and then publish or subscribe to data TOPICs. Very often, IIoT network scenarios are dynamic meaning thousands of devices can leave a network too. DDS ensures that large numbers of devices can join or leave a network automatically.
How is data transfer flexibility achieved?
DDS provides 25 different quality of service (QOS) configurations. This means data subscribers can choose communication profiles appropriate to their requirements.
Examples of DDS QOS configurations are:
• History: Specify how much data history is available to new network participants;
• Reliability: Specify whether data receipt can be tolerant of dropped packets;
• Deadline: A network mechanism that will error-handle late delivery of messages;
• Filtration: A subscriber may not want to receive every data sample for a particular topic;
• Ownership Strength: A subscriber can choose which duplicate data to use based on publisher strength.
Who uses DDS?
DDS is used in a very wide range of industrial sectors where advanced connectivity is required. The following use case descriptions are some of many:
Defence: DDS is widely used in defence vehicles for providing a communication backbone for all vehicle subsystems, including weapons, driveline, ramps, navigation and data logging. In this type of application, bridges are made from CANBUS to DDS in order to create a common data space.
DAQ and Instrumentation: DAQ networking has always traditionally been constructed on a point to point architecture. DDS gives DAQ applications a completely data centric approach. DAQ modules can communicate with each other, individual sensors, remote servers for bulk data logging and display/diagnostic devices.
Energy: The trend to switch to renewable energy means that large numbers of individual power generation devices have to be controlled. Wind turbines, solar farms and hydro installations all now have to be able to be switched on an off according to demand. Highly distributed network architectures are used with DDS being the command, control and feedback protocol. DDS provides control signals that open/close contactors and then feedback to command software that monitors how much power each device is producing.
Is DDS a new concept?
Despite its sophisticated capabilities, DDS has in fact been in existence since 2001. It was started as a solution to problems with stove pipe communications in US Navy applications. DDS was designed to provide a data centric communications environment for seaborne applications to enable many different sub systems to communicate.
As an established technology, DDS is an open standard with multiple vendors and a governing standards body, the Object Management Group (OMG). As there are multiple vendors of DDS, there is no commercial lock-in with any implementation. Vendor meetings under the governance of OMG meet four times per year to discuss improvements and changes.
What if my IIoT device has limited resources?
Hamersham is the European distributor for Twin Oaks Computing, which makes a world-leading small footprint DDS implementation, CoreDx. Flash requirements are 600Kb and memory requirements for a typical application is <250Kb. This means the Twin Oaks CoreDx DDS can be deployed in edge applications where resources are limited or larger cloud computers where resources are readily available. Twin Oak CoreDx allows the same DDS implementation to be implemented regardless of application type.
The Hamersham Twin Oaks partnership offers DDS builds for a very wide range of architectures and operating systems. With a deeply embedded background, DDS builds can be made for a variety of architectures – ARM, X86, PPC, MIPS and Aurix – in addition to various operating systems including Windows, Linux, VxWorks, IOS, Android, Greenhills Integrity, PikeOS, Threadx, FreeRTOS, QNX and Erica.
Hamersham will be able to build a system that incorporates specific requirements, in addition to offering free valuations.
Hamersham is the UK and European distribution partner for Twin Oaks Computing’s CoreDX DDS, which is suitable for use in a variety of applications including automotive, aerospace, manufacturing, automation and power transmission.
For more information, please visit www.hamersham.com
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