Industrial communication

Recently however, the adoption of Ethernet, the well known LAN, is being proposed at all levels of factory automation systems. Such a new prospect has some indubitable benefits. In particular, the very high communication speeds will allow for reduced transmission times, whereas the expected standardization of Ethernet components for industrial application will offer the possibility of employing the same network components throughout the factory. Moreover, a very clear and stable growth of the network bandwidth is envisaged in the next years.

The most important obstacle toward the achievement of the above scenario has been the uncertain suitability of Ethernet for operation at the device level. However, it is a matter of fact that the enhancements of the last years (i.e. the adoption of switch devices, which practically eliminated the collisions, and the considerable increasing of the transmission speed) have made the behaviour of Ethernet satisfactory also for such a level. Moreover, adequate protocols have been designed in order to handle the specific data traffic.

Our goal is to investigate recently introduced industrial Ethernet protocols (Ethernet/IP by OVDA, PROFINET by PROFIBUS International, etc) in order to evaluate real performances and applicability. OPNET is currently used to build model of emerging protocols in order to perform simulations of large industrial networks. See our on going thesis projects

Wireless Sensor Networks

Wireless sensor applications are growing thanks to their low installation cost. However some problems still remain when wireless technology is used. In particular, attention of the researcher is focused on safety and power consumption issues; a reliable communication and a low-consumption (i.e. low maintenance) are needed for high-end automation applications. Moreover, factors like the spatial distribution of sensors, wireless transmission range and the traffic on the shared medium affect the overall behavior of the underlying application and therefore the expected results.

Our goal is to implement new wireless technologies (ZigBee, Bluetooth, WirelessUSB, WiFi, GSM etc), obtaining working prototypes and efficient power saving protocols. OPNET will be used to evaluate routing protocols and communication protocols before their implementation.

Work on progress

Evaluation of Industrial Ethernet Synchronization Protocols

by Paolo Foletti

If hard real-time is to meet the requirements of motion control applications, the communication system must guarantee deterministic behaviour. Only a few special field buses currently achieve cycle times of less than a millisecond, or jitter values down to a microsecond. Networked automation systems using Ethernet require special measures to achieve comparable or better determinism. Accepting variance in Ethernet transmission propagation times, a solution to guarantee deterministic system behaviour might be the use of a precise clock in all terminal devices; clearly such clocks must be synchronised each other.

The Precision Time Protocol embodied in IEEE1588 provides a solid basis for real time industrial Ethernet. Using the new IEEE Standard Precision Time Protocol (PTP) IEEE1588 approved in November 2002, it is possible to synchronise to less than a microsecond local clocks in sensors, actuators and other terminal devices using the same network that transports process data. Existing time sync protocols do not achieve the required accuracy or convergence speed.

Example of PTP timing and event ordering

The goal of thesis project, which is under development in OPNET environment, is to build models of emerging synchronization protocols, in order to evaluate the performances and the industrial applicability. In particular in the ambit of Industrial Ethernet, we realize a OPNET model of the IEEE Standard Precision Time Protocol (PTP) IEEE1588, in order to perform simulation of large industrial network.

The project is articulated on three levels of abstraction: net model, node model and process model.

Example of OPNET network scenario for PTP IEEE1588 model simulation

At net level, in order to estimate the behaviour of various network topology, we develop the models for the devices typical of the PTP IEEE1588 protocol (i.e. Ordinary clock and boundary clock) and we make use of network components models already present in OPNET (i.e. switch, router and link).

OPNET model of UDP over IP on Ethernet network stack

In the node model, with the purpose of build a PTP clock model based on standard clauses indications and simulation requirements, we adding new modules to the UDP over IP on Ethernet stack model, already present in the OPNET node models. To assure the possibility to use various typologies of network traffic and guarantee model versatility, we maintaining all the modules of stack UDP over IP, even if outside the actual scope of our simulation.

Detail of PTP IEEE1588 protocol engine model developed

Finally, at process model level, we develop the PTP protocol engine, assuring all the functionalities and details useful for a complete simulation of the synchronization protocol behaviour.

Moreover, by OPNET Editors we organize instruments to support simulation like header file of common C functions and data types, packet formats, model of particularly components (i.e. Quartz oscillator or GPS device for the generation of PTP clock local time) and the specific interfaces between various processes of the network node stack.