C²I² Press Release
With a modern society that is relying to a great extent on industrialisation, automation and communication, the applicability and impact of real-time, mission-critical, distributed systems is gaining importance. The capabilities and performance of real-time network protocols are fundamental to the operation of these systems.
C²I² Systems managing director, Richard Young, has identified a complete set of protocols, tools and techniques, within the framework of a coherent implementation paradigm that can be used to synthesise these complex, network-based computer systems.
He says that, while a systems solution for the present timeframe is identified, a methodology is also proposed which will systematically enable the requirements of next generation systems to be matched to the capabilities and characteristics of technologies of the future.
"In general, analogue and dedicated digital control techniques are almost entirely obsolete due to their modest performance, high maintainability requirements and almost complete lack of flexibility," says Young. "Investigation of business, industrial process control and military command and control systems indicates that digital computer-based systems have superseded these systems, at least in the West.
"Distributed system solutions have been proposed to be superior to centralised architectures for the reasons of survivability, dependability, affordability, reconfigureability and upgradeability. Point-to-point connection schemes in distributed architectures have been shown to be severely limiting, especially with regard to flexibility and upgradeability.
"Moreover, with the application of appropriate technologies and techniques, as identified by C²I² Systems, local area networks have been shown to be appropriate for a broad range of real-time, mission-critical distributed systems."
Young argues that LANs are ideal for distributed architectures in that they can provide an optimum system solution in terms of the derived system requirements.
He says the proposed architectures are thus contended to support a good compromise of federalism, performance and cost-effectiveness. They are also very flexible in terms of system design options, scalability and on-line reconfiguration, as well as system upgrade.
"However, the design of real-time, mission-critical, distributed systems using computer networks requires special attention to a number of critical issues, especially timing, synchronisation, fault-tolerance techniques, system engineering management and dataflow management," he says.
"Central to these issues is that of network protocols. These must offer real-time performance and support the requirements of dependability and fault-tolerance in order to support mission-critical applications. These protocols span the entire network system, or profile, that is, from the physical layer to the application interface layer.
"The performance of each layer is critical in order not to create bottlenecks which would compromise the real-time performance of the system. Also critical are the interfaces between each layer of the profile, both in terms of performance and robustness. Of specific significance is the interface to the application user, where system-specific requirements exist.
"Considering the extent of the problem space, as well as the spectrum of implementation options that are available, derivation of an optimum, network-based system solution for distributed systems can be complex," says Young.
However, for real-time, mission-critical systems, a straightforward process of elimination considerably restricts the solutions pace when the fundamental issues are considered."
These are :
"Once these requirements and capabilities are established, C²I² Systems concludes that, in the present timeframe, the system network solution reduces to the employment of the FDDI in a dual- or quad-redundant topology operating over multimode fibre optic media. FDDI in a dual-redundant configuration exhibits excellent scalability from small implementations to large, making its potential application domain extensive."
Young says that while FDDI will support present real-time systems designs, those of the future will require much higher performance networks.
In the medium term, throughputs of some 600 Mbits-1 are likely to be required by real-time control systems, in the long term throughputs of some 3 Gbits-1 are likely to be required, escalating to 10 Gbits-1 in the very long term.
Young predicts the Protocol Engineer will gain a new lease on life when high data rates start finding application outside the network backbone.
"While dedicated and optimised protocol processors may not be required for data transfer rates of up to 100 Mbits-1, general purpose processors will almost certainly be unable to cope with gigabit data rates," he says.
ATM is a technology being supported by many players, many with their own vested interests, as the standard next generation high-speed network.
Young contends this will not be realised in the short to medium term for three reasons; the complexity of the technology, the cost of ATM switching equipment and the lack of major progress to date in the standardisation effort.
Due to the extensive interest in ATM, both academic and financial, Young says it will become the standard high speed network in three to 10 years. It will initially be appropriate and find application in WAN and MAN topologies, mainly public networks, and this will initially be at speeds in the range of 622 to 2 048 Mbits-1.
"But, ATM does not intrinsically provide fault tolerance (compared to FDDI dual counter-rotating ring). Special techniques will have to be employed to achieve fault-tolerance. This is not likely to be without considerable cost. ATM also provides no error control over payload data. This may be a limiting factor for very low latency transfers which require complete integrity.
"The current maturity of ATM standards and technology does not support the present implementation of mission-critical, real-time systems.
"Despite the above limitations, ATM has definite advantages in multimedia application due to its high bandwidth and low latency," he says.
Fibre Channel (FC) refers to a set of standards under development by the ANSI Fibre Channel committe, X3T9.3. Fibre Channel specifies a high-speed serial data channel that can connect nodes point-to-point or through a switch or a switch network (switch fabric). FC was initially conceived as a peripheral interconnect channel, but its definition has developed such that it could support the construction of high performance local area networks.
FC supports a number of different link options, from shielded twisted pair supporting 200 Mbits-1 over 50 m and up to singlemode fibre supporting 800 Mbits-1 over 10 km.
"Fibre Channel is a very flexible and high performance network technology. It is a definite contender for next generation systems, including real-time, mission-critical applications. However, only the lower speed (100 Mbits-1) versions of FC are presently mature enough for immediate implementation.
"While the ATM versus FDDI debate will continue furiously for a few years, common sense will dictate that the majority of network managers will match their current and future applications to the technology which supports it more fully today and which allows for an upgrade path.
"And network managers electing FDDI can rest assured in the knowledge that many vendors of FDDI are planning strategies to allow smooth transitions to ATM and Fibre Channel in the future when they are standardised and accepted by the commercial market place," concludes Young.