HomePublicationsPhD Thesis

A Multiple Logical Ring Approach to Real-time Wireless-enabled PROFIBUS Networks
Ref: HURRAY-TR-051102       Publication Date: 1, Nov, 2005

Abstract:
Fieldbus communication systems have become a common solution to the problem of interconnecting sensors, actuators and control devices in manufacturing automation and process control applications. Recently, there has been an enormous eagerness to extend fieldbus functionalities to support wired and wireless network stations in the same network.
This thesis addresses the proposal of a novel architecture for a hybrid fieldbus communication system, where wired and wireless transmission media coexist.
The RFieldbus European project was one major effort towards a hybrid wired/wireless fieldbus solution. Although some of the achievements could potentially be applied to other commercial-off-the-shelf (COTS) standard fieldbuses, most of the effort in that project was devoted to an actual implementation over PROFIBUS (acronym for PROcess FIeld BUS) technologies. In our opinion, the arguments that were put forward in favour of using PROFIBUS as the federating communication system for such architecture are still valid. In RFieldbus, the interconnection of wired and wireless stations is based on interconnecting devices operating at the Physical Layer level (as repeaters). In this thesis, we propose an alternative approach where the interconnecting devices act as bridges, thus operating at the Data Link Layer level.
The hypothesis is that such a bridge-based approach is devisable and presents, from the timeliness and reliability perspectives, advantages over the RFieldbus approach.
One of the contributions of this thesis is the specification of the Inter-Domain Protocol (IDP) which enables the execution of transactions between stations belonging to different media, i.e. transactions that must be relayed through one or more bridges. The IDP specifies the behaviour of the bridges when processing such kind of transactions, how the response can be obtained from the responder station (attached to another medium) and the format of the frames exchanged between bridges. The IDP builds upon the operational characteristics of the PROFIBUS-DP Application Layer, therefore guaranteeing full compatibility with this protocol.
In the proposed architecture, wireless stations can move between different wireless cells.
In order to support this functionality, this thesis also proposes the Inter-Domain Mobility Procedure (IDMP). This protocol includes several operational phases, with the objective of being fully transparent to the system applications by guaranteeing no communication errors and no order inversion of frames. Therefore, the IDMP is compatible with standard PROFIBUS stations. The IDP and the IDMP lead to additional communication delays, in relation to a standard PROFIBUS network, due to periods of network inaccessibility and the intrinsic operation of the IDP. Therefore, a timing analysis of the IDP is proposed. This analysis is then extended for integrating the effects of the IDMP on message transactions. These methodologies constitute a tool enabling the support of real-time applications. The thesis also shows the advantages of the proposed architecture over the RFieldbus approach, namely in terms of responsiveness to network errors, in terms of fault containment and it terms of timeliness for message transactions within the same network domain.

Luis Lino Ferreira

Document:

View
PDF Download
PDF