1. Ganesh Panatula, Nagabhushan S.V, Dr. T. V. Suresh Kumar / International Journal of Engi-
neering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.1371-1375
Integration Analysis Of Safety Critical Systems In Information
Technology
1
Ganesh Panatula, 2 Nagabhushan S.V, 3Dr. T. V. Suresh Kumar
1( Associate Professor , Dept. of MCA,BMSIT)
2(Assistant Professor, Dept. of MCA,BMSIT)
3(Professor&HOD , Dept. of MCA, MSRITT,)
Abstract
Safety-critical systems are those systems computer hardware, other electronic and electrical
whose failure could result in loss of life, significant hardware, mechanical hardware, and operators or us-
property damage, or damage to the environment. ers, not just the software element.
There are many well known examples in applica- Safety critical software has been traditional-
tion areas such as medical devices, aircraft flight ly associated with embedded control systems. As
control, weapons, and nuclear systems. The em- awareness of how systems can impact safety has de-
phasis of this paper is on the software element of veloped, the scope of safety critical software has ex-
safety critical systems, which for convenience is panded into many other types of systems.
often referred to as safety critical software. Many An obvious example of a safety critical sys-
modern information systems are becoming safety- tem is an aircraft fly by wire control system, where
critical in the sense that their failure results in fi- the pilot inputs commands to the control computer
nancial loss and even loss of life. Future safety- using a joystick, and the computer manipulates the
critical systems will be more common and more actual aircraft controls. The lives of hundreds of pas-
powerful. From a software perspective, developing sengers are totally dependent upon the continued cor-
safety critical systems in adequate numbers and rect operation of such a system.
with adequate dependability is going to require Moving down to earth, railway signaling
significant advances in areas such as specification, systems must enable controllers to direct trains, while
architecture, verification, and process. The cur- preventing trains from colliding. Like an aircraft fly
rent project work is regarding fault tolerance by wire, lives are dependent upon the correct opera-
client-server system that addresses safety-critical tion of the system. However, there is always the op-
issue in the web application by suing smart server tion of stopping all trains if the integrity of the sys-
approach. tem becomes suspect. It is not possible to just stop an
aircraft while the fly by wire system is in use. [1].
Keywords: Fault Tolerance System, Safety Critical Software in medical systems may be directly
System responsible for human life, such as metering safe
amounts of X-rays. Software may also be involved in
NOMENCLATURE: providing humans with information, such as informa-
ADS- Autonomous Distributed System tion which a doctor uses to decide on medication.
ASCM-Adaptive Safety Critical Middleware Both types of system can impact the safety of the pa-
DESCS-Distributed and Embedded Safety- tient.
Critical Systems Big civil engineering structures are designed
FCS - Flight Control System on computers and tested using mathematical models.
FTS - Fault Tolerant System An error in the software could conceivably result in a
FMEA- Failure Mode and Effect Analysis bridge collapsing. Aircraft, trains, ships and cars are
PHL - Preliminary Hazard List also designed and modeled using computers. Even
PHA- Preliminary Hazard Analysis something as simple as traffic lights can be viewed as
QOS -Quality of Service safety critical. An error giving green lights to both di-
SCP -Self-Checking-Pair rections at a traffic junction could result in an acci-
SCS -Safety Critical System dent. Within cars, software involved in functions
such as engine management, anti-lock brakes, trac-
I. INTRODUCTION tion control, and a host of other functions, could po-
A safety critical system is a system where tentially fail in a way which increases the likelihood
human safety is dependent upon the correct operation of a road accident.
of the system. The emphasis of this paper is on the A well conceived and executed safety case is
software element of safety critical systems, which for a key element in bringing a safety critical system into
convenience is often referred to as safety critical use. In areas which have been traditionally concerned
software. However, safety must always be considered with safety critical systems, such as the aviation in-
with respect to the whole system, including software, dustry and the nuclear industry, a certification body
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2. Ganesh Panatula, Nagabhushan S.V, Dr. T. V. Suresh Kumar / International Journal of Engi-
neering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.
will have to be convinced that a system is safe before analyze their system even before hardware as well as
it is put into use. In some other areas, users have their software realization. Also, nowadays, the cost of de-
own safety monitoring groups. Nevertheless, the vast veloping a critical system increases exponentially
majority of software safety is entirely in the hands when system design errors are found after the imple-
and conscience of the software developers and sup- mentation or integration of the system. In this paper,
pliers. a model driven approach is described for design and
development of a safety critical system. The stated
II. LITERATURE REVIEW approach is described along with functional descrip-
By the analysis of the previous research tion of electrical system architecture and the concept
done on safety critical systems, we highlight some of of modeling. Self-Checking-Pair (SCP) based com-
the major research done by the research scholars on puter architecture with high speed communication
safety critical issues. bus interface is modeled and the performance is eva-
The work proposed by Qing Sun Lirong et luated before its hardware and software realization
al. [2] states that there are three states in safety criti- The work proposed by Kumagai S et al. [5]
cal manufacturing systems namely working, fail-safe explains that to secure modern complex system activ-
and fail-dangerous states. This paper studies two dif- ities, rigid and heavily centralized organization is ra-
ferent safety-critical parallel-series models by consi- ther obstacle. To facilitate quick decision, mutual col-
dering their components’ lifetime distribution pos- laboration, and to maintain performability in
sessing general forms. The indices of reliability and unexpected severe situation, autonomous decision
safety, including the probabilities that the system in unit should act at best in intelligent way by itself. Au-
these states and mean time for the system under two tonomous distributed system concept plays a central
different failure ways, are derived respectively. Vari- role for operating complex systems commonly exist-
ous corresponding indices comparisons between the ing in today’s networked society of 21st century. This
two different parallel-series system models, and paper explains the effectiveness of ADS system para-
among the series, parallel and parallel-series systems, digm to secure safety critical systems and clarifies
are conducted. Some illustrative numerical examples key issues to realize the objective as intended.
are employed to show the procedures. The derived The work proposed by Hovakimyan N et al
indices formulae are without component lifetime dis- [6] narrates about the development of L1 adaptive-
tribution assumptions, which have significant mean- control theory and its application to safety critical
ings for reliability analysis and safety design of the flight control system (FCS) development. Several ar-
system. chitectures of the theory and benchmark examples are
The work proposed by Zhang Yi et al. [3] analyzed. The key feature of L1 adaptive-control ar-
states that Distributed and embedded safety-critical chitectures is the decoupling of estimation and con-
systems (DESCS) are those systems whose failure trol, which enables the use of arbitrarily fast estima-
could result in loss of life, significant property dam- tion rates without sacrificing robustness. Rohrs's
age, or damage to the environment. Because of the example and the two-cart system are used as bench-
nature of DESCS, designing the applications for mark problems for illustration. NASA's flight tests on
DESCS is harder than those for distributed real-time subscale commercial jet verify the theoretical claims
embedded systems. In this paper, a multilevel em- in a set of safety-critical test flights.
bedded safety-critical middleware called adaptive
safety-critical middleware (ASCM) is described that III. MOTIVATION FOR THE PAPER
provides related services to ease the development of Today, most of the safety critical systems
embedded safety-critical applications. It also presents use a combination of the following architectures.
a multi-layer end-to-end adaptive QOS management
technology to satisfy the dynamic and unpredictable [a] Intrinsic Fail-Safe Design: This is generally used
mission requirements of DESCS. for discrete mechanical or electrical components
The work proposed by By Nisha, G.R. [4] where the credible failure modes of all components
describes that faults in safety critical systems are the can be directly analyzed to ensure no unsafe condi-
important elements to be avoided. To avoid these er- tions are created as a result of failure. Most systems
rors or faults, Fault Tolerant Systems (FTS) are use this technique as some portion of their system de-
evolved. But still, some more hidden design faults are sign, particularly for I/O or comparison mechanisms
not weeded out before realization by traditional and identifies a minimum set of credible failure modes to
life cycle tests and analysis. In this paper, an ap- be included in the analysis.
proach has been described to find out these types of
faults by simulating system architecture with model- [b] N-version programming: This technique requires
ing and simulation. By this model based methods, at least two software programs, executing together
one can enable early verification of the system and and performing identical functions. An independent
quickly find errors or faults and deal with it. This is a team using independent tools must write each soft-
very attractive approach, since the systems are criti- ware program. They may or may not run on indepen-
cal systems. Through this method, one can test and dent hardware platforms.
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3. Ganesh Panatula, Nagabhushan S.V, Dr. T. V. Suresh Kumar / International Journal of Engi-
neering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.
[c] Numerical Assurance: This technique requires on client data, maintaining their data for 24/7 is very
that the state of each safety-critical parameter be crucial for them, but there are internal and external
represented by a large encoded numerical value. Off- factor which creates negative impact on their busi-
line data structures are defined such that real-time ness, if they lose the data. Maintain the same data in
permissive results can only be calculated (by pseudo- multiple places lead to data redundancy and also it is
randomly combining these values) when all the prop- expensive. Since processing of data takes place at dif-
er conditions for a permissive result are present. ferent levels and in different versions, keeping track
With the above said architectures, we high- of data in the consistent manner, it is very difficult.
light the importance of safety verification & valida- So we investigate the above problem and solve it by
tion. It is necessary to provide verification to all the using smart server approach. We design a framework
identified unacceptable or undesirable hazards so that to architect safety critical system for web application
they have been properly mitigated. In order to do this, and it is implemented by taking case study as an ex-
all of the safety-critical functions necessary to im- ample and show case how our approach is suited for
plement the system (down to a very low level) must web application.
be identified. Functions that have to be implemented Our framework is viewed from two core perspec-
must be implemented fail-safely. The fail-safe im- tives.
plementation means that we look at all the credible a) Server Perspective: In the server, business criti-
failures that could occur and make sure that occur- cal data is stored and clients are accessing the
rence of any one of them (or combination of failures data for the live business transactions. Suddenly
in the event that the first failure is not self-evident) processing of the data stop’s by external factors
maintains the system in a safe state, either by forcing like server down, application crash, unexpected
the system to a stop (or other safe state such as a less execution of some unknown event, virus intru-
permissive signal) or by transferring control to a sec- sion etc and client has to wait until the applica-
ondary system (e.g. redundant computer). tion in the server is up. From the client perspec-
As part of verification & validation in SCS, tive, this unexpected event is very expensive and
Functional Fault Trees are a widely accepted tool for no patience to wait. If the server scalability and
identifying the safety-critical functions from the top performance issue is not handled during design
down. These trees start at the upper level hazards and development, there are every chances that
previously identified and branch down through the client may lose huge amount (scenario can be
system, subsystem and interfaces to identify all of the understood in online trading). To address the
functions that, if not performed correctly, could pre- above issue, we introduce a middleware compo-
cipitate the upper level hazards. The functional fault nent in terms of proxy server which can create
trees provide a top-down analysis of the system. A instances of running application in the dynamic
Failure Mode and Effect Analysis (FMEA) is also environment In our approach, when unexpected
used to provide a bottom-up analysis of the system. event arises which stops the client from dynamic
Starting at the component level, all credible failures access,, an event is triggered and notification will
are analyzed to verify that they do not create any un- go to the proxy server , In that server, from
safe condition. It provides guidance on credible com- where main server has stopped the execution,
ponent failure modes. As with all safety analyses de- proxy server takes the responsibility to process
scribed so far, secondary failures must be considered the remaining computation and put it in the off-
in combination with the initial failure if the initial line mode and store that part of information in a
failure is not self-revealing. file and from that file, information will be passed
Based on the above research findings, it is to client. Hence client will have continuous ac-
intended to design a safety critical system for web cess to data. At the time when main server noti-
application and its implementation is showcased fies about its failure to proxy server, there will be
through a case study. some lag time which is unnoticeable at the client
end.
IV. PROPOSED WORK
It is intended to design and implement safety b) Client Perspective: Since clients are accessing
critical system for web Application based on n-tier the data continuously in critical applications
client server system. We analyze the safety critical is- stopping the application for a minutes will incur
sues that are addressed in client -server system by huge loss as the data is tracked every minute for
providing fault tolerance using smart server ap- some analysis (scenarios can be understood re-
proach. garding the data coming from the satellite)[7],
hence continuous access for the data is very
Issues in client server system much required. Client should have authentication
In the corporate world, more prominence is to access the application and it can be any gen-
given to data and securing data is the major concern eral Client Server setup application. At any point
for them to maintain confidence and long term rela- of time, the client should be assured to have con-
tionship with the clients. Since they heavily depend
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4. Ganesh Panatula, Nagabhushan S.V, Dr. T. V. Suresh Kumar / International Journal of Engi-
neering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.
tinuous connectivity with the server without any the server is down abruptly, the client has to
disruptions. wait for the server to be up, in traditional approaches.
By considering the above two perspectives, we Now, our approach suggests that inspite of server
study and analyze and implement safety critical sys- breakdown the client still can continue with normal
tem though case study for web application and ex- operation. The methodology to facilitate the above is
periment in our lab. below.
At the time of server eventuality, the soft-
Case Study: ware component (COMP) detects the server failure
Assume an application is installed in the and the recent updated information in the server is
server machine and accessed by n clients (n=5, in- loaded to the Proxy server. At this juncture, the proxy
itially). Here clients access the application by know- server acts as a normal server and caters to the needs
ing server IP address which is run in their browser in of client. In this process, care will be taken to avoid
the following format http: // ipaddress/application. data redundancy. Once the main server is up, the
We assume all the systems are interconnected COMP notices the same and loads back the recent
through LAN. Each client is provided with an inter- updated information to the main server from the
face to login to the server. Each client accesses the proxy server. Now main server resumes its normal
server for different purpose, like downloading, up- work.
loading, reading documents etc. Now, if During the process of switching, as stated
above, the time gaps need to be measured and re-
SCS
duced to the optimal extent.
FRAMEWO
RK V. CONCLUSION
Safety critical software is a complex subject.
The approach discussed in this paper, is to make the
SMART SERVER system more reliable and to reduce the time gaps of
APPROACH context switching between main and proxy servers, in
the web application environment. The custom appli-
cation discussed in case study will provide a good
example for simple approach to address the safety
critical issue of fault tolerance in the client server ap-
C Proxy Clien plication by providing the user with simple interface
t -1 to interact with system and application availability in
BUSINE O Serv- both online and offline condition.
SS er
M ACKNOWLEDGEMENT:
CRITICA Clien We thank all the authors for the information support.
L DATA P t -2
VI. FUTURE WORK
The scope of the work can be extended to
reduce the time gap between main sever and proxy
server. Also, once the main server resumes normalcy,
Clien data stored in the proxy server can be deleted there-
by avoiding redundancy of data.
t -3
In- REFERENCES
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neering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
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