Constrained Application Protocol (CoAP) is a software protocol that was designed to support the connectivity of simple low power electronic devices (e.g. wireless sensors) with Internet based systems. The Internet Engineering Task Force (IETF) Constrained Restful Environments (CoRE) Working Group is currently working on standardizing CoAP.
CoAP is targeted for small low power sensors, switches, valves and resource constrained internet devices such as Wireless Sensor Networks (WSNs) implementing the IETF’s emerging IPv6 over Low Power Wireless Personal Area Networks (6LoWPAN) standard. This new standard enables the use of IPv6 in Low-power and Lossy Networks (LLLNs) such as those based on IEEE 802.15.4. It is designed to easily translate to HTPP for simplified RESTful web integration.
CoAP supports a client/server programming model based on a RESTful architecture in which resources are server controlled abstractions made available by an application process and identified by Universal Resource Identifiers (URIs). CoAP is lightweight, simple and runs over UDP (not TCP) with support for multicast addressing enabling a single request to be issued to multiple CoAP devices concurrently.
The Object Management Group's (OMG) Data Distribution Service for Real-Time Systems (DDS) is an open middleware standard that enables scalable, real-time, dependable, high performance and interoperable data exchanges between publishers and subscribers. It is based on a proven data-centric paradigm that emerged from Defense and Aerospace but which is now being rapidly adopted in sectors as diverse as Power Generation, large scale SCADA, Air Traffic Control and Management, Smart Cities, Smart Grids, Vehicles, Medical Devices, Modeling and Simulation, and Financial Trading.
DDS makes data a first class citizen in the system thanks to its extensive support for keys, lifecycle management etc. DDS is brokerless and provides the abstraction of a virtual Global Data Space, a ubiquitous, universal and fully distributed data cache. DDS also provides a standard API as well as an interoperable wire protocol.
CoAP is useful for data collection in systems that do not require very high performance, real-time data sharing or real-time device control. In many cases data is collected for subsequent "offline" processing. A CoAP device is connected to cloud-based system via a HTTP proxy using a standard COAP-HTTP mapping. Using a proxy/bridge adds an additional communication overhead and increases message latency.
In comparison, only DDS can provide the real-time, many-to-many, managed connectivity required by high-performance device-to-device applications.
A key component of the Vortex DDS product suite is Vortex OpenSplice, the leading (open source and commercial) implementation of the DDS standard.