Implementation of Telecontrol Applications over GPRS Networks

Authors: Aitor Arzuaga Munsuri, Jose Miguel Arzuaga Canals and Mikel Zamalloa Aiartzaguena, uSysCom, Spain

Introduction

Given that GPRS operator networks are public, the implications of this fact are examined from the utility’s point of view, and finally we list the most important aspects to be considered in order to perform a successful implementation of a telecontrol system over GPRS.

Companies in the electric sector have a multitude of SCADA Telecontrol systems which operate with protocols aimed at serial ports, for example IEC 60870-5-101, DNP3... Historically, communication with remote sites has been performed using the electric company’s private communications channels, such as SDH networks, PDH, VHF and microwave radio or others. This option was the only one available capable of covering the communication requirements for the provision of service.

In the present day, companies are under increasing pressure to reduce infrastructure operating costs, but at the same time maintain (or increase) the availability and reliability of their communications. As such, new methods of communication are being explored to allow them to do so. A clear alternative is the use of public communications networks, using a service provided by an operator. One option which has been used for some time is data calls, either over a fixed or mobile (GSM) network.

In recent years, with the development and progressive implementation of packet switching technologies over mobile networks (GPRS/UMTS/EDGE), a new range of possibilities has opened up which may make them viable for telecontrol applications. On the one hand, a TCP/IP-based service is offered, which guarantees the reception of traffic and the “always online” nature of this type of service. Further, charges based on exchanged traffic volume, as opposed to circuit switching connections which are charged by connection time, may be a very attractive feature for utilities. Only the traffic actually exchanged is paid for.

Nevertheless, each of the telecontrol protocols which were once designed for implementation using serial ports have their peculiarities which make direct use over a TCP/IP network, with the inherent latency of a GPRS network, problematic and even unviable. There are a number of determining factors which must be considered for telecontrol communications to be rolled out appropriately and reliably. On the other hand, the main source of reluctance to using GPRS networks on the part of electric companies lies in the difficulty in monitoring and verifying the level of service provision promised by the mobile services operator, given that this comprises an aspect which the electric company does not possess a sufficient level of control over or means to verify.

This article summarises all of the aspects which must be considered in order to successfully and reliably establish a telecontrol application over GPRS, and details the parameters and methods which must be taken into account by the electric company to control the quality of service provided by the operator.

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