=Paper=
{{Paper
|id=Vol-1830/Paper10
|storemode=property
|title=A Review of Computer Network Reliability
|pdfUrl=https://ceur-ws.org/Vol-1830/Paper10.pdf
|volume=Vol-1830
|authors=Godwill Udoh,Caroline Alenoghena,Bala A. Salihu
}}
==A Review of Computer Network Reliability==
https://ceur-ws.org/Vol-1830/Paper10.pdf
International Conference on Information and Communication Technology and Its Applications
(ICTA 2016)
Federal University of Technology, Minna, Nigeria
November 28 – 30, 2016
A Review of Computer Network Reliability
Godwill Udoh, Caroline Alenoghena, and Bala A. Salihu
Department of Telecommunications Engineering, Federal University of Technology, Minna, Nigeria
godwilludoh@gmail.com, carol@futminna.edu.ng, salbala2000@hotmail.com
Abstract—Network reliability, as a field, is focused on There have been efforts by researchers using various
questions of topological disconnection between data nodes. approaches in determining the reliability of a computer
Computer network reliability problem is primarily resolved by network and as such are view to classify the approaches and
calculating the probability that specific set of nodes in define most suitable method of analyzing understudied
understudied network can speak with each other at a given Computer network is needed.
time. Network reliability analysis cuts across the design, In this paper a review of computer network reliability
deployment and testing of computer networks. Review reveal analysis is carried out and presented in five subheadings.
two major approaches to reliability analysis of computer Section 2 gives the different approaches to reliability
network these are Path/cute numeration and Case analysis
analysis of computer networks, section 3 give an overview
which utilizes the concept of graph decomposition. The
measures of computer network reliability analysis include
of related works, section 4 describe the model used, section
issues on connectivity, capacity and travel time. The different 5 describes the measures of reliability analysis, section 6
parameters used in defining the reliability of computer- gives a description of different parameters that can affect
communication system include; Failure Rate, Mean Time To network reliability, section 7 gives the evaluation of the
Repair, Mean Time Between Failures, Mean Time To Failure reliability index and conclusion is presented in section 8.
and Availability.
Keywords-reliability analysis; computer network; reliability II. DIFFERENT APPROACHES TO RELIABILITY ANALYSIS
index; network reliability OF COMPUTER NETWORKS
Network Reliability defines the probability that an
I. INTRODUCTION understudied Network can perform its stated function to an
acceptable level of performance for some given period of
Effective communications is critical in determining the
time [1]. Any specific measure of reliability, thus, depends
economic, social, innovative and military prowess of
on the nature of the desired function and what levels of
modern day society; this is hinged on the fact that effective
performance are acceptable. Earliest works on Network
communications is a key stone in all human activities. This
reliability was around 1950, with connectivity of networks
communication is majorly effected by data nodes. A data
been used as there liability index [2].
node could be a mobile phone, information centers,
Different set of algorithms are employed in reliability
encrypting and decrypting machines which have evolved
analysis of computer networks. The algorithms used can be
into what we call computers in today‟s world. Thus, the
grouped into two:
design and deployment of reliable data nodes has been given
a high priority and this has enhanced the study of Computer A. Path/Cut Enumeration:
Network reliability analysis as a field on its own. Network
reliability is concerned with the topological disconnection This entails the listing of all the simple paths between
between data nodes. Computer network reliability problem end nodes. These represent a complete set of favorable
is primarily resolved by calculating the probability that (unfavorable) non-disjoint events. Simple paths are links
specific set of nodes in understudied network can speak in the network that connect set of nodes while prime cut sets
with each other at a given time. Network reliability analysis are links in the network which when disconnected cause the
cuts across the design, deployment and testing of computer network to fail. The simple paths are considered assets of
networks. favorable events while the prime cuts as set of unfavorable
As communication is now centered on computer events. Reliability analysis entails summing the terminal
networks, the design of reliable computer networks is much reliabilities of these paths which is an indication that each
needed. Reliability analysis of a computer-communication node communicates with a designated node. To obtain the
network gives “worthiness test” of the infrastructure or computer network reliability, the inclusion-exclusion
relevant components that constitute the computer network techniques of path and cuts is carried out. More efficient
and as such, seeks to evaluate the relevance of the computer techniques based on Boolean algebra, can be utilized [2]–
network to its intended design expectations. [7].
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International Conference on Information and Communication Technology and Its Applications (ICTA 2016)
B. Case analysis: cater for issues of power supply, equipment malfunctioning
Case analysis uses the method of graph decomposition. and working environment) in the reliability analysis of
This entails the creation of subsets from the path sets, either computer networks
around a reference edge or around a number of It is important to note that Failures in computer networks
edges/links/paths. A reference edge is simply the node from cannot be completely eliminated and, hence, reliability can
which the factoring is anchored. When more than one edge never be 100 percent. In order to reduce their negative
is considered, graph decomposition is restricted to a impact on end-to-end connectivity, redundancy techniques
conservative policy as against an exhaustive one. Using a are implemented on network routing so as to ensure a proper
conservative policy minimizes the number of disjoint events alternate (backup) path is available upon failure of the
in the analysis. Disjoint events are simple paths that are not primary working path.
connected or have common node. This decomposition Performances of networks can be measured by
simplifies the analysis and helps cancel out occurrence of comparing with the reliability index. The reliability index
parallel links. represents the probability that a network operates. The
performance of a design can be studied by changing the
topology of the network. This is achieved by adding,
removing or replacing some components so as to augment
III. OVERVIEW OF RELATED WORKS
the reliability or for satisfying certain specifications.
Most of the works reviewed evaluate the reliability of
understudied Networks by the methods of minpaths and
mincuts. A minpath is the shortest distance/path/ number of
hops between nodes needed to keep them up and IV. MODELS USED IN COMPUTER NETWORK RELIABILITY
communicating while mincut is the smallest break in the
link/network that renders the link/network ineffective. An Models used to describe computer networks help to
aggregation of paths between nodes is called pathsets while define a frame in which the network could be studied. From
an aggregation of cuts in the network is called cutsets. papers researched, the common model used for Computer
As a network enlarges and nodes increase, the number of Network is the Stochastic Model.
minpaths and mincuts increase exponentially. Effective A stochastic network [24] describes a physical system in
analysis of these sets needed to keep the network up or down which each node and/or each edge (directed or undirected)
via optimization methods help in estimating the reliability of can fail independently and failure one element does not
understudied networks. affect another network element. A number representing the
Genetic algorithm as an optimization tool was used in non-failure probability is assigned to the element. With this
evaluating the reliability of networks [8]-[11]. model, the network reliability analysis problem is solely
Wei-Chang Yeh [12] in his work used Particle Swarm calculating the probabilities of failure/operation for the edges
Optimization and Monte Carlo Simulation in analyzing the and/or nodes needed to establish link connectivity [25].
pathsets in order to evaluate the reliability In the Reliability analysis of Computer Networks
Monte Carlo simulation was also employed in [13] [14] (especially Ring Networks) [37], the following assumptions
to analyze the pathsets/cutsets in order to evaluate the are made (depending on the number of components
reliability understudied network. understudied):
Wei Hou [15] in his thesis, analyzed the reliability of Components are either operational or failed at any
networks with software and hardware failures. He developed given time and Component state is a random event,
models; MORIN – Modelling Reliability for Integrated s, independent of any other.
Networks and SAMOT – Simplified Availability Modeling The reliability of a network component is the
Tool, with which he used in analyzing the Network. probability that it is operational at a given time.
Boolean reduction technique was also used in evaluating The Channel Capacity, C, is fixed and C » B (where
the reliability of understudied network [16] – [21] B is the provisioned Bandwidth/Capacity for the
Mathematical Analysis are also employed in the Network).
reliability analysis of networks [22] – [23]. Failure of any electronic component in a station,
An overview of works reviewed shows that little have including the power supply, causes the station to fail
been done on reliability analysis of Ring topology networks Network reliability does not include the probability
(this might be a ripple-effect from the fact that most for failure of attached hosts since they are external to
computer networks implement the mesh topology for its the understudied communications subnetwork.
obvious advantages).
Earlier works seem to use survivability, availability,
susceptibility, connectivity and reliability interchangeably. The components used to define the node in the
These mentioned parameters are distinct and a field of study understudied network are the link, port and station itself. The
on themselves. station define the system health and caters for power issues
Modern communication networks are made up of reliable in the node. Failure/success probabilities of these component
components and failed components are quickly repaired. are independent of each other but have an overall effect on
Multiple connections which allow for rerouting of traffic the state of the node.
when network failure occurs is also a common feature. With The port comprises the transmitter, receiver and the
the afore-stated in mind, it is important to take into account inbound/outbound link used in effecting self-healing when a
the connection ports, links and state of the nodes (this should fault occurs.
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International Conference on Information and Communication Technology and Its Applications (ICTA 2016)
V. MEAURES OF COMPUTER NETWORK RELIABILITY Failure Rate (FR) is the number of failures
A good index for measuring the utilization of a computer experienced or expected for a device divided by the
network reflects that a network fails gradually and that some total equipment operating time.
nodes (links) are more important than others. The stated Mean Time to Repair (MTTR) is the total time taken
index is not also based on traffic patterns. Measures with the to effect corrective maintenances divided by the total
above requirements include; terminal, “capacity-related”, number of these repairs.
and “travel-time related” reliability measures. Mean Time between Failures (MTBF) is the mean
time expected between failures, measured in hours.
A. Terminal Reliability For constant failure rate systems, MTBF is the
Terminal Reliability is the probability that there exists an inverse of the Failure Rate.
end-to-end connection between two or more nodes in a Equation 1givesthemathematical formula for
computer network needed to keep the network up and evaluating MTBF
running [9]. There are basically 3variants;K-Terminal,2-
Terminal and All-Terminal Reliabilities. (1)
1) K-Terminal Reliability: The predominant measures of
reliability when applied to computer networks are mainly Mean Time to Failure (MTTF) is the mean time
specialized cases of k-terminal reliability. This is defined as expected before the first failure of a piece of
the probability that a path exists and connects k-terminals equipment. It is meant to be the mean over a long
(nodes) within the network [26] -[28].This reliability is the period of time and a large number of units.
sum of the probabilities of disjoint success paths [29]. Availability (A) is the probability of a system to
2) Two Terminal Reliability: This is the probability that being operational when called upon to perform its
a path exists between end pair of nodes in the network [30]- function. Availability and unavailability (1-A) are
[32]. often expressed as probabilities.
3) All Terminal Reliability: This is the probability that
Equation 2 gives the mathematical formula for
the nodes in a network are communicating with each other
determining the availability of the network.
[33][34]. Two terminal and all- terminal reliability are
modifications on the K- Terminal measure where K=2 and
K=n (n is the number of nodes in the network), respectively. (2)
B. Capacity-Related Network Reliability VII. EVALUATION OF COMPUTER NETWORK RELIABILITY
INDEX
This field is an extension or specialization of the
research in computer network reliability. It is acknowledge Reliability analysis of a computer network invariably
that not all links (edges) may have the same capacity leads to evaluating a reliability index for the network. This
(weight, bandwidth). Further, it is also considered that the is implied sincere liability, like availability, is expressed as
capacity demanded of the network is variable. Capacity- probabilities. A reliability index defines a scale on which the
Related computer network reliability defines the network reliability of a computer network can be measured. This
reliability in terms of the bandwidth (variable or fixed) scale ranges from 0–1. A value of zero implies a failed
needed to establish efficient data-throughput between nodes network while one means an “excellent” reliable network.
[35] [36]. It places a bench mark requirement (bandwidth) The computer network reliability performance parameters
needed for connectivity between node shaving fixed or described above are used in the evaluation of Reliability (R)
variable link capacities. It is used when the data requirement index of the network.
is same or more than the channel bandwidth and/or
subscribed bandwidth. Computationally we have;
C. Travel Time Network Reliability (3)
This basically defines the time taken for data to travel
between link ends or nodes. It also describes the time taken (4)
for a hand shake to occur between specific nodes in a
network and uses this as an index to measure reliability (‘T’ is the number of hours)
VI. COMPUTER NETWORK RELIABILITY PERFORMANCE For multiple components;
PARAMETERS
Network reliability cannot be fully defined without (5)
taking into consideration some parameters that affect
computer network performance. Different parameters that („n‟ is the number of components in the system)
affect network reliability of a computer-communication
system are described below [37]. They include failure rate, 𝑛
𝑅(𝑇) = 𝑖=1 𝑅𝑖(𝑇) (6)
Meantime to repair, mean time between failures, mean time
to failure and availability.
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International Conference on Information and Communication Technology and Its Applications (ICTA 2016)
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