Over the past two years, the Network Control Systems Branch (Code 532) has been investigating control and status networking technologies. These emerging technologies use distributed processing over a network to accomplish a particular custom task. These networks consist of small intelligent 'nodes' that perform simple tasks. Containing simple, inexpensive hardware and software, these nodes can be easily developed and maintained. Once networked, the nodes can perform a complex operation without a central host. This type of system provides an alternative to more complex control and status systems which require a central computer. This paper will provide some background and discuss some applications of this technology. It will also demonstrate the suitability of one particular technology for the Space Network (SN) and discuss the prototyping activities of Code 532 utilizing this technology

Fortin, Andre

Patel, Manoj

English

NASA Technical Reports Server

N94-21335
DISTRIBUTED INTELLIGENT CONTROL AND STATUS NETWORKING
Andre Fortin
Manoj Patel
NASA/G0ddard Space Flight Center
Network Control Systems Branch
Greenbelt, MD 20771
Summary
Over the past two years, the Network Control Systems Branch (Code 532) has been investigating
control and status networking technologies. These emerging technologies use distributed
processing over a network to accomplish a particular custom task. These networks consist of
small intelligent "nodes" that perform simple tasks. Containing simple, inexpensive hardware
and software, these nodes can be easily developed and maintained. Once networked, the nodes
can perform a complex operation, without a central host. This type of system provides c.n
alternative to more complex control and status systems which require a central computer. This
paper will provide some background and discuss some applications of this technology. It will
also demonstrate the suitability of one particular technology for the Space Network (SN) and
discuss the prototyping activities of Code 532 utilizing this technology.
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Introduction
Over the last two years, under a research project, the Network Control Systems Branch (Code
532) at Goddard Space Flight Center has been investigating distributed intelligent control and
status networking technologies. These emerging technologies use distributed processing over a
network of smart devices or "nodes" to accomplish a particular custom task, like home
automation, without a central host. These networks are designed to be simple and inexpensive
for an engineer to develop and implement a custom task. This paper will provide some
background and discuss some applications of this technology. It will also demonstrate the
suitability of one particular technology for the Space Network (SN) and discuss the prototyping
activities of Code 532 utilizing this technology.
Background
A continuing trend to convert from centralized to distributed intelligent control and status
systems seems to have become widespread. A wide spectrum of systems designed for industrial
automation, building controls, automobiles, and consumer products are following this trend. The
reasons for this trend are numerous.
Centralized control and status systems consist of remote sensors that provide feedback to a
central microcontroller, which in turn sends signals to monitors and actuators. Each centralized
control system is unique with its own input/output and processing requirements. It consists of
large computational engines that process the inputs and outputs of a whole suite of sensors and
equipment and relay the changes and actions to the appropriate targets. These systems axe
expensive to develop and install, and very difficult to expand and maintain on an
ongoing basis.
Intelligent distributed control and status systems consist of nodes with embedded intelligence
where each node performs a simple task. Nodes may be devices such as proximity sensors,
switches, motion detectors, and relays. While individual nodes in this system perform a simple
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task, the entire system performs a complex operation such as automation of a building, factory
or a house, without the need for a central host.
Intelligent distributed control systems have a number of significant benefits over centralized
control systems. These systems have lower starting costs by using simple and common methods
of communicating between all nodes of the system, like using one protocol. The networking
nature of these systems facilitates graceful growth by easing expansion and reconfiguration.
These systems cut installation costs by sharing common wiring among nodes. Finally, the
flexibility of these systems allows many diverse products and applications to interoperate.
Existing networking technologies such as local area networks (LANs) could be used to network
these distributed processing systems. However, the Ethernet protocol used to operate a LAN
would be an overkill for the requirements of a control and status network. Ethernet is designed
to move huge amounts of user documents, data bases, and graphics files among computers, file
servers, and printers. A control/status network involves moving relatively short data frames
carrying command and status information that trigger actions within devices. Ethernet is much
more complex than what is necessary for a control/status network. A control/status scenario
could be implemented with a LAN. Such a system, however, would be a large, expensive
development effort with complex hardware and software for each node. New technologies have
recently been introduced that provide a full package of hardware and software development
tools, a microprocessor or microcontroUer, I/O interfaces for interfacing to sensors and
actuators, a network operating system, and a communications protocol to develop these
distributed intelligent control and status networks.
Examples of Uses
Targeted uses of distributed intelligent control and status networks include industrial, home, and
office automation. Particularly custom uses are known to exist for cars and mobile homes.
These environments have special needs. The nodes must be small, inexpensive, and sometimes
use existing wiring. Some of theses networking technologies have multiple physical media
available to allow for node to node communication, such as existing power lines, RF, and twisted
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pair cable,
A good example frequently given by distributed intelligent control and status networking
vendors is a system that controls and monitors common equipment found in the home or office.
Consider a node in every device, such as the power outlets, the lights, the light switches, the
smoke detector, the major appliances, and the security system. Such a system, in the event of a
fire, could disable power going to the outlets, flash the overhead lights near emergency exits, turn
off major appliances, like a furnace, and perhaps turn on the security system (if there is no fire
alarm, like in a home). This would all be accomplished without a central host. The smoke alarm
node would detect the smoke and send the appropriate messages to the applicable nodes. All of
these nodes would be networked via the AC power.
Another good example is a system to simplify the wiring in a vehicle. In the dash board and
steering column of a vehicle, large amount of cables run from the passenger compartment to the
engine department to control various devices around the car. The lights (rear brake lights,
parking lights, and headlamps) are just one subsystem within a vehicle that needs controlling
from the operator. Presently these devices are controlled by many devoted wires running from
the steering column/dashboard to the individual lamps. Consider one wire running between
everything, the headlamps, the brake lights, the parking lights, and the switches/controls. Each
lamp would contain a node that would control it and each switch/control in the passenger
compartment would also have a node. These nodes would signal each other based on operator
input. The headlamp node would turn on the high beam if it received a signal from a switch
node located near the operator. Because of the networking nature of this technology, the parking
light node would ignore the message to activate the high beam since this message is not for that
node.
From the previous examples, it can be seen that this networking technology provides for
simplification of wiring and providing for automation. Other features include simplicity of
engineering and maintenance. Nodes, like in the previous example, that are designed to be light
nodes can be generic. Specific features of a light node can be determined at installation time and
not at manufacturing time. A building engineer or home owner would not have to stock various
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light nodesfor repair,specialfeatureslike blinkingduringafire alarm(assumingthenodeis the
closestlight to anescapeexit) canbeprogrammedat installationtime. Easeof engineeringis
alsoa goodtrait of thesetechnologies,dueto thenatureof thesimplehardwareandprocessors
usedin thenodes.
Thereareseveralvendorsthat offer these technologies in which some are very focused on a
particular application. General Motors has a system called CAN, targeted for vehicle automation
and control. CEBus, a home automation standard, is available free for any manufacturer to
design nodes for. The Local Operating Network (LON), designed by Echelon Corporation, is a
flexible technology that can be used in many applications and environments. It may be well
suited for systems here at NASA. All of these proprietary distributed intelligent control and
status systems can provide homes, offices, industrial plants, and large systems with simple
methods to meet their control and status needs.
Local Operating Networks (LON)
The current control/status systems in the Space Network are centralized and card-caged.
Some of these systems involved a considerable amount of design and development effort and are
very difficult to expand and maintain. Additionally, the equipment utilizes a number of different
interfaces such as GPIB, MS 1553, RS232, and RS422. The control systems for this scenario
have dedicated, point-to-point connections to each equipment. Therefore, interoperability
between the equipment is a major problem that demands a large amount of software
overhead and processing requirements from the centralized computer system. LON offers a
single chip, networking solution to these problems that is inexpensive, modular, interoperable,
flexible, and easy to develop. Other control/status networking technologies that were considered
were focused on particular applications and did not provide the flexibility demanded by the
Space Network systems, This technology has the most potential for successfully replacing or
complementing a variety of centralized data processing, data distribution, and fault isolation and
monitoring systems within the Space Network.
The technology centers around a single VLSI chip called the Neuron. This inexpensive,
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multiprocessorchip (lessthan$10) implements a multitasking network operating system, a
networking protocol that conforms to the 7 layer OSI model, and a flexible input/output
interface through built-in device drivers. Neuron chips provide all the necessary functionality to
intelligently process a node's inputs and outputs and relay that information to other nodes over a
local network. One Neuron is required for every node on the distributed control and status
network. A variety of nodes can be designed each serving different functions. Once these nodes
are created and communicating among themselves, a distributed processing control and status
network called a LON is created.
The integrated hardware/software development system of LON allows the engineer to easily
design and test a small, simple node with custom hardware tied to the Neuron's generic I/O
interface and custom application software that defines the functionality of the node on the
network. This software is written in a unique, network programming language called Neuron C.
This proprietary language is an extended version of ANSI C that provides support for new data
types, statements, and function libraries. These enhancements optimize the chip for hardware
interfacing to I/O devices and real-time, node-to-node communications on a network.
Neuron C shields the programmer from the hardware details of input/output processing, the
protocol details of the physical medium being used, and the details of packet generation,
addressing, and transmission. This makes the application software short and simple and spares
the programmer from learning a new protocol. The development system allows the engineer to
thoroughly debug the node's hardware with this application code through a process of single-
stepping through hardware breakpoints. The development system's capability for network
management and monitoring allows the engineer to test the nodes with other nodes on a
prototype network on this system and manage the network once all the nodes are installed and
operational. Thus, LON's integrated development environment makes node design quick and
easy.
The protocol in which these Neuron-chip based nodes talk to each other is called LONTALK.
This 7-layer protocol has been optimized for movement of relatively short data frames carrying
control/status information. It provides support for multiple transmission media which include
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twistedpair (whichrunsfrom 4.9Kbpsto 1.25Mbps),radiofrequency(4.9Kbpsto 625Kbps),
powerline(10Kbps), andevencustommediato suit thedesigner'sspecificneeds.Theprotocol
is actuallytransparentto themediumused,allowingavarietycustomdistributedcontrol and
statusnetworksto beeasilycreated.
LON technology simplifies the development and maintenance of distributed, intelligent control
and status networks by providing an inexpensive communications and control processor, an
integrated hardware/software development system, and a control/status networking protocol in
one package. Thus, these distributed nodes are designed, developed, tested, and installed with
minimum effort and time. Adding a new node to the system is simply a matter of connecting it
to the network and making other nodes on the network aware of the new node. Thus, expansion
is simplified. The LONTALK protocol solves the problem of interoperability among different
nodes. Thus, Local Operating Networks resolves the problems of increased node development
time, increased installation costs, difficult expansion, and a lack of interoperability currently
experienced in the design of centralized control and status systems.
Prototyping Activities of Code 532
After researching into several distributed intelligent control and status networking technologies,
Code 532 decided to evaluate the LON technology. Under a research project, Code 532 procured
the necessary hardware and software to evaluate and prototype LON. A technical paper was
written that describes in detail what was accomplished in the research and evaluation phase of
the LON. Technical information can be found in this paper located in the Code 532 branch
library.
After the research and evaluation phase, a prototype system using LON was placed in an
operational environment in the Network Control Center (NCC). This system, called the Block
Rate Monitor (BRM), consists of a block counter, a gateway, and a host computer. The block
counter is a LON node that passively monitors four NASCOM lines. This node counts the
number of NASCOM blocks per second and checks for clock presence. The statistical data is
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then passed over a LON dedicated twisted pair cable to the gateway. The gateway is also a LON
node that converts data sent over the LON to RS-232. This protocol converter allows a
workstation to interface to the LON. The workstation receives the statistical data and provides
the operator with bargraphs (see figure 1) and stripcharts (see figure 3) to evaluate existing
traffic. The operator can also graph logged data for a historical perspective of line traffic (see
figure 2). The workstation logs 20 days worth of traffic statistics for four NASCOM lines.
Figure 1. Example main window with bargraphs. Figure 2. Example of historical data
Figure 3. Example strip chart output from BRM application (driven with random data).
With the Block Rate Monitor, the operator can conveniently monitor, in real time, the line
activity from a console. The operation of a transmitting system can be deduced as well. If it is
not generating any blocks, the system could be down, or there could be a bad cable or patch.
This system has already been used to determine if line rate increases were needed (from 112Kb/s
vp
to 224Kb/s), but these monitored lines do not have heavy traffic loads and therefore an increase
in the line rate was not approved. This system is a very small LON. It only consists of two LON
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nodes,a block counter,anda gateway.Thenextphaseof our prototypinga control and status
network in an SN environment will greatly expand the LON and the concept of remote traffic
monitoring.
The second prototype system is called the Data Integrity Monitoring System (DIMS). This
system will consist of 40 LON nodes that each monitor a NASCOM line. Each node, or Data
Integrity Monitor (DIM), accumulates statistical data of one NASCOM line and is physically the
size of 2 cigarette packs. The cost of each node will be around $350. These nodes can count
blocks, evaluate the CRC, count bad blocks, determine the clock rate, and detect inverted data.
With each node monitoring different NASCOM lines, a LON of nodes is created that relays line
activity to the operator. Just as in the first prototype, a gateway receives the status information
from each DIM and sends it to a workstation.
This workstation will have a new application that will allow the operator to use this system for
performance monitoring, fault isolation, and traffic monitoring. With DIMs located on the inputs
and outputs of a system, performance monitoring would be achieved. By comparing the graphs
of the traffic on the input and the outputs, a time difference should be observed and indicate the
time it took for a block to be processed. Since the workstation application has detailed physical
diagrams of the site interconnections along with traffic gauges on the lines, fault isolation would
be achieved by an operator noting that a line showing no activity should, in fact, have some
activity. This would direct the operator to step back in the diagram of the system, to find the
break in the system. The operator would have to determine by this application, which patch
panel has been mispatched, which cable has gone bad, or which system has failed.
Our prototypes, utilizing the LON technology, are concepts similar to the Small Network
Management Protocol (SNMP). SNMP is designed for Ethernet and works with Ethernet host
computers. The DIMS, on the other hand, can incorporate any communication line protocol
monitor and works as a layer on top of the existing communications lines. The advantages for a
DIMS approach include passiveness, non-interference with operational communication
lines/systems, and a multi-protocol line/system monitoring. The advantage for an SNMP
approach would be a software only system that monitors Ethernet systems on existing Ethemet
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host machines. SNMP is more inexpensive and simple, but is limited to Ethernet.
Future plans in these prototyping activities include building nodes that monitor other
communication lines (like MIL-STD-1553, GPIB, and Ethernet) and expanding the system to
monitor every communication line in the NCC. Future nodes will be much smaller and cost
under $150.
Conclusion
Distributed intelligent control and status networking offers a new and unique solution to the
traditional methods of performing control and status. The problems of increased development
time, lack of flexibility, lack of interoperability, difficult expansion, and difficult maintenance
that we face with centralized control and status vanish with this new method of networked
control and status.
Local Operating Networks appears to be on the forefront of this new trend by offering an
inexpensive, flexible solution that resolves all of the problems experienced in the design of
centralized control and status systems. Our prototyping efforts will determine this technology's
feasibility to the Space Network systems.
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Kleiner, Art. "The Ultimate Control Chip: The Programmable World." Popular Science.
May 1992, pp. 90 - 95.
LonWorks Products 1992. USA: Echelon Corporation, 1992.
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