Technical Paper Abstract
The idea of the Internet of Things to act and sense in the physical world have opened up for new innovations within the communication technology area. A resource constrained device such as a sensor can hardly handle the complexity of a transport protocol like TCP to produce a simple sensing value when it also must consider limited resources in terms of computation power and energy. There are multiple communication protocols under development targeting Internet of Things devices that have achieved reliable communication with minimal resource usage both on the device and on the network. Inspired by previous work in extending EtherNet/IP™ to resource-constrained industrial things this paper investigates the Constrained Application Protocol (CoAP) and the possibility to adapt it to the CIP™ protocol. CoAP is a transport protocol built upon the IP and the UDP protocol designed for use with constrained devices and constrained networks. Previous work put the responsibility to handle the lost reliability on the application when replacing the TCP protocol with UDP. Investigations shows that this is not necessary. For resource constrained devices, handling small amounts of data, CoAP together with UDP replaces the TCP protocol with only a 4-byte fixed header and a compact encoding of options for additional information without compromising the reliability of the network. CoAP supports confirmable and non-confirmable messages, has a basic set of methods to interact with resources of a device and identifies resources by using Uniform Resource Identifiers (URIs). This design conforms well to the CIP protocol which requires handling of explicit messaging and IO connections, possibility to address objects and attributes of the CIP object model and services to interact with those. CoAP together with single pair Ethernet would create a good communication solution for resource constrained industrial things. With the coming transition to IPv6 there will also be several wireless physical layers suitable for resource constrained devices such as the Bluetooth wireless technology, 6LoWPAN and the ZigBee Standard. With a device level network using IP addressing the CIP networks could over time converge towards one common addressing mechanism. To take advantage of the features of CoAP, IP addressing on the device level network and multiple physical layers for constrained devices this paper presents a proposal of how CoAP can be adapted to CIP to handle explicit messaging and IO connections to resource constrained industrial things of a CIP network.
Paper and presentation from the 2017 Industry Conference & 18th Annual Meeting of Members
Jonas Green, HMS Industrial Networks
Björn Otterdahl, HMS Industrial
CoAP, IPv6, DTLS, Industrial Internet of Things