Understanding Network Routing Problem and Study of Routing Algorithms and Heuristics through Implementation

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 11 | Nov -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 686
Understanding network routing problem and study of routing
algorithms and heuristics through implementation
Saumya Shandilya
Saumya Shandilya, Computer Science Department, Symbiosis Institute of Technology, Pune.
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Abstract - In this project, we intend to identify, understand
and compare various routing algorithms used in real world
networks.
The various objectives of this research are :
1. Define and understand the concepts of routing.
2. Determine if a Greedy or Dynamic Programming strategy
algorithm is more efficient for routing, ingeneral. Identify
which strategy is used more in real world networks.
3. Identify the common routing algorithmsusedinnetworks.
Identify which algorithms are used in which scenarios.
4. Identify the performance metrics for gauging algorithms.
5. Compare existing routing algorithms in variousscenarios
(on the simulation software). Also note specific
phenomena or anomalies during simulation.
6. Think of modifications (if any) in existing routing
algorithms, or devise a new routing algorithm.
Key Words: Routing, Throughput, Latency, Greedy
Strategy, Dynamic Programming
1. INTRODUCTION
The transport layer provides communication service
between two processes running on two different hosts. In
order to provide this service, the transport layer relies on
the services of the network layer, which provides a
communication service between hosts. In particular, the
network-layer moves transport-layer segments from one
host to another. At the sending host, the transport layer
segment is passed to the network layer. In order to this, the
network layer requires the coordination of each and every
host and router in the network. In simpleterms,ifwehaveto
define Routing in a lay man’s language we can simply say
that Routing is the manner/order in which we decide the
path a segment shall follow from the sending host to the
receiving one. This path includes a connection of links and
routers. In technical terms though routing is a complex yet
challenging concept.
Technically, Routing broadly consists of the following 3
functions:
1. Path Determination: This function determines the
path/route the packets will follow from the sender to
receiver. It involves various routing algorithms which
are discussed further.
2. Switching: When a packet arrives at a router it needs to
be further dispatched to other routers i.e. it is further
switched to other routers.
3. Call Setup: Just like a TCP carries out 3 -way handshake
similarly some network layer architectures (e.g., ATM)
requires that the routers along the chosen path from
source to destination handshake with each other in
order to setup state before data actually begins to flow.
In the network layer, this process is referred to as call
setup.
The main goals of routing are:
Correctness: The routing should be done properly and
correctly so that the packets may reach their proper
destination.
Simplicity: The routing should be done in a simple manner
so that the overhead is as low as possible. With increasing
complexity of the routing algorithms the overhead also
increases.
Robustness: Once a major network becomes operative, it
may be expected to run continuously for years without any
failures. The algorithms designed for routing should be
robust enough to handle hardwareandsoftwarefailures and
should be able to cope with changes in the topology and
traffic without requiring all jobs in all hosts to be aborted
and the network rebooted every time some router goes
down.
Stability: The routing algorithms should be stable under all
possible conditions.
Fairness: Every node connected to the network should get a
fair chance of transmitting their packets. This is generally
done on a first come first serve basis.
Optimality: The routing algorithms should be optimal in
terms of throughput and minimizing mean packet delays.
Here there is a trade-off and one has to choose dependingon
his suitability.

Fig -1: Connected devices through routers
Routing is performed for many kinds of networks, including
the telephone network (circuit switching), electronic data
networks (such as the Internet), and transportation
networks. This article is concerned primarily with routing in
electronic data networks using packetswitching technology.
In packet switching networks, routing directs packet
forwarding (the transit of logically addressed network
packets from theirsource toward their ultimate destination)
throughintermediate nodes.Intermediatenodesaretypically
network hardware devices such
as routers, bridges, gateways, firewalls, or switches.General
purpose computers can also forward packets and perform
routing, though they are not specialized hardware and may
suffer from limited performance.Theroutingprocessusually
directs forwarding on the basis of routing tables, which
maintain a record of the routes to various network
destinations. Thus, constructing routing tables, which are
held in the router's memory, is very important for efficient
routing. Most routing algorithms use only one network path
at a time. Multipath routing techniques enable the use of
multiple alternative paths. In case of overlapping/equal
routes,algorithmsconsider the following elements to decide
which routes to install into the routing table (sorted by
priority):
Prefix-Length: where longer subnet masks are preferred
(independent of whether it is within a routing protocol or
over different routing protocol)
Metric: where a lower metric/cost is preferred (only valid
within one and the same routing protocol)
Administrative distance: where a route learned from a more
reliable routing protocol is preferred (only valid between
different routing protocols)
2. RESEARCH ELABORATION
2.1 Algorithmic strategies used in routing
1. Brute force algorithm
2. Greedy strategy
3. Dynamic programming
4. Backtracking
5. Branch and Bound
6. Divide and Conquer
7. Decrease and Conquer
8. Transfer and Conquer
2.2 Types of Routing Algorithms
1. Link state routing:
Link-state routing protocols are one of the two main classes
of routing protocols used in packet switching networks
for computer communications, the other being distance-
vector routing protocols. Examples of link-state routing
protocols include open shortest path first (OSPF)
and intermediate system to intermediate system (IS-IS).The
link-state protocol is performed by every switching node in
the network (i.e., nodes that are prepared to forward
packets; in the Internet, these are called routers). The basic
concept of link-state routing is that every node constructs
a map of the connectivity to the network, in the form of
a graph, showing which nodes are connected to which other
nodes. Each node then independently calculates the next
best logical path from it to every possible destination in the
network. The collection of best paths will then form the
node's routing table. This contrasts with distance-vector
routing protocols, which work by having each node share
its routing table with its neighbours. In a link-state protocol
the only information passed between nodes is connectivity
related. Strategy used : greedy programming, generally a
variant of Dijkstra's algorithm is used.
2. Distance vector routing:
In computer communication theory relating to packet-
switched networks, a distance-vectorroutingprotocol isone
of the two major classes of intra domain routing protocols,
the other major class being the link-state protocol.
Distance-vector routing protocols use the Bellman–Ford
algorithm, Ford–Fulkerson algorithm, or DUAL FSM (in the
case of Cisco Systems's protocols) to calculate paths. A
distance-vector routing protocol requires that a router
inform its neighbors of topology changes periodically.
Compared to link-state protocols, which require a router to
inform all the nodes in a network of topology changes,
distance-vector routing protocols have less computational
complexity and message overhead. The term distance
vector refers to the fact that the protocol
manipulates vectors (arrays) of distances to other nodes in
the network. The vector distance algorithm was the original
ARPANET routing algorithm and was also used in the
internet under the name of RIP (Routing Information
Protocol). Examples of distance-vector routing protocols
include RIPv1 and IGRP.
Strategy used : dynamic programming, generally bellman
ford algorithm.

4. Dijkstra's Algorithm
Algorithm:
Each node j is labeled with Dj, which is an estimate of cost
of path from node j to node 1. Initially, let the estimates be
infinity, indicating that nothing is known about the paths.
We now iterate on the length of paths, eachtime revisingour
estimate to lower values, as we obtain them. Actually, we
divide the nodes into two groups ; the first one, called set P
contains the nodes whose shortest distances have been
found, and the other Q containing all the remaining nodes.
Initially P contains only the node 1. At each step, we select
the node that has minimum cost path to node 1. This node is
transferred to set P. At the first step, this corresponds to
shifting the node closest to 1 in P.Its minimum costtonode1
is now known. At the next step, select the next closest node
from set Q and update the labels correspondingtoeachnode
using :Dj = min [ Dj , Di + dj,i ]. After N-1 iterations,
shortest paths for all nodes are known, and the algorithm
terminates after completing these many iterations.
Principle:
Let the closest node to 1 at some step be i. Then i is shifted to
P. Now, for each node j , the closest path to 1 either passes
through i or it doesn't. In the first case Dj remains the same.
In the second case, the revised estimate of Dj is the sumDi +
di,j . So we take the minimum of these two cases and update
Dj accordingly. As each of the nodes get transferred to set P,
the estimates get closer to the lowest possible value. Whena
node is transferred, its shortest path length is known. So
finally all the nodes are in P and the Dj 's represent the
minimum costs. The algorithm is guaranteed to terminatein
N-1 iterations and its complexity is O( N2 ).
5. The Floyd Warshall Algorithm
This algorithm iterates on the set of nodes that can be used
as intermediate nodes on paths. This set grows from a single
node ( say node 1 ) at start to finally all the nodes of the
graph. At each iteration, we find the shortest path using
given set of nodes as intermediate nodes, so that finally all
the shortest paths are obtained.It is observed that all the
three algorithms mentioned above give comparable
performance, depending upon the exact topology of the
network.
3. RESULTS AND FINDINGS
3.1 Performance metrics for comparison
Router metrics are metrics used by a router to make routing
decisions. It is typically one of many fields in a routing table.
Metrics are used to determine whether one route should be
chosen over another.The routingtablestorespossibleroutes,
while link-state or topological databases may store all other
information as well. For example, Routing Information
Protocol uses hopcount (number of hops) to determine the
best possible route. The route will go in the direction of the
gateway with the lowest metric. The direction with the
3. Bellman-Ford Algorithm
Notation:
Di = Length of shortest path from node 'i' to node 1.
di,j = Length of path between nodes i and j .
Common Routing Algorithms:
The shortest paths are calculated using suitable algorithms
on the graph representations of the networks. Let the
network be represented by graph G ( V, E ) and let the
number of nodes be 'N'. For all the algorithms discussed
below, the costs associated with the links are assumed to be
positive. A node has zero cost w.r.t itself. Further, all the
links are assumed to be symmetric, i.e. if di,j = cost of link
from node i to node j, then d i,j = d j,i . The graph is assumed
to be complete. If there exists no edge between two nodes,
then a link of infinite cost is assumed. The algorithms given
below find costs of the paths from all nodes to a particular
node; the problem is equivalent to finding the cost of paths
from a source to all destinations.
This algorithm iterates on the number of edges in a path to
obtain the shortest path. Since the number of hops possible
is limited (cycles are implicitly not allowed), the algorithm
terminates giving the shortest path.
Notation:
d i,j = Length of path between nodes i and j,
indicating the cost of the link.
h = Number of hops.
D[i,h] = Shortest path length from node i to node 1, with
upto 'h' hops.
D[ 1,h] = 0 for all h .
Algorithm :
Initial condition : D[ i, 0] = infinity, for all i ( i != 1 )
Iteration : D[i,h+1] = min{ di, j+ D[j,h] }over all values of j
Termination : The algorithm terminates when
D[i, h] = D [ i, h+1] for all i .
Principle:
For zero hops, the minimum length path has length of
infinity, for every node. For onehoptheshortest-pathlength
associated with a node is equal to the length of the edge
between that node and node 1. Hereafter, we increment the
number of hops allowed, (from h to h+1 ) and find out
whether a shorter path exists through each of the other
nodes. If it exists, say through node 'j', then its length must
be the sum of the lengths between these two nodes (i.e. di,j )
and the shortest path between j and 1 obtainable in upto h
paths. If such a path doesn't exist, then the path length
remains the same. The algorithm is guaranteedtoterminate,
since there are utmost N nodes, and so N-1 paths. It has time
complexity of O ( N3 ) .

lowest metric can be a default gateway.Router metrics can
contain any number of values that help the router determine
the best route among multiple routes to a destination. A
router metric typically based on information like path
length, bandwidth, load, hopcount,pathcost, delay, Maximum
Transmission Unit (MTU), reliability and communications
cost.
A Metric can include:
1. measuring link utilization (using SNMP)
2. number of hops (hop count)
3. speed of the path
4. packet loss (router congestion/conditions)
5. latency (delay)
6. path reliability
7. path bandwidth
8. throughput [SNMP - query routers]
9. load
10. MTU
Fig -2: Six network evaluation criteria
THROUGHPUT: In general terms, throughput is the rate of
production or the rate at which something can be processed.
When used in the context of computer networking, such
as Ethernet or packet radio, throughput or network
throughput is the rate of successful message delivery over a
communication channel. The data these messages belong to
may be delivered over a physical or logical link or it can pass
through a certain network node/router. Throughput is
usually measured in bits per second (bit/s or bps), and
sometimes in data packets per second (p/s or
pps).The system throughput or aggregate throughput is the
sum of the data rates that are delivered to all terminals in a
network. It can be analyzed mathematically by applying
the queueing theory, where the load in packets per time unit
is denoted as the arrival rate (λ), and the throughput, in
packets per time unit, is denoted as the departure rate (μ).
GOODPUT:In computernetworks, goodput istheapplication
level throughput, i.e. The number of useful
information bits delivered by the network to a certain
destination per unit of time. The amount of data considered
excludes protocoloverhead bitsaswellasretransmitteddata
packets. This is related to the amount of time from the first
bit of the first packet sent (or delivered) until the last bit of
the last packet is delivered. For example, if a file is
transferred, the good put that the user experiences
corresponds to the file size in bits divided by the file transfer
time. The good put is always lower than the throughput (the
gross bit rate that is transferred physically), which generally
is lower than network access connection speed.
NETWORK LATENCY: Network latency in a packet-
switched networkismeasuredeither one-way (thetimefrom
the source sending a packet to the destination receiving it),
or round-trip delay time (the one-waylatencyfromsourceto
destination plus the one-way latency from the destination
back to the source). It further consists of the processing
delay, queuing delay and transmission delay. The processing
delay is basically the time a sender host takes to process a
packet and identify the router. Once the router is identified,
queuing delay is encountered when a packet has to wait in
the queuing buffer before it is transferred further.
Transmission delay consists of the time to transmit the
packet over the link.
LINK CAPACITY: The term link capacity defines the net bit
rate (aka. Peak bit rate, information rate, or physical
layer useful bitrate), orthe maximumthroughput ofalogical
or physical communication path in a digital communication
system. For example,bandwidthtests measurethemaximum
throughput of a computer network.
NUMBER OF BOTTLENECKS: Bottleneck basically means
traffic/congestion at various points in the network link. The
number of bottlenecks signifies the number of place
throughout the network link where a bottleneck has
occurred.
TRAFFIC INTENSITY:Inadigitalnetwork,thetrafficintensity
measures the ratio of the arrival rate of packets to the
average packet length. Is: (al)/R where a is the average
arrival rate of packets (e.g. In packets per second), L is the
average packet length (e.g. In bits), and R is the transmission
rate (e.g. Bits per second).
Performance metrics selected for the implementation of this
project:
1. Throughput
2. Delay
3.2 Software and testing environment
A network simulator is software that predicts the behaviour
of a computer network. SincecommunicationNetworkshave
become too complex for traditional analytical methods to
provide an accurate understanding of system behaviour
network simulator are used. In simulators, the computer
networkistypicallymodelledwithdevices,links,applications
etc. and the performance is analyzed. Simulators typically
come with support for the most popular technologies and
networks in use today. Most of the commercial simulators
are GUI driven, while some network simulators

are CLI driven. The network model/configuration describes
the state of the network (nodes, routers, switches, links) and
the events (data transmissions, packet error etc.). An
important output of simulationsarethe trace files.Tracefiles
log every packet, every event that occurred in the simulation
and are used for analysis. Network simulators can also
provide other tools to facilitate visual analysis of trends and
potential trouble spots.
Simulation of networks is averycomplextask.Forexample,if
congestion is high, then estimation of the average occupancy
is challenging because of high variance. To estimate the
likelihood of a buffer overflow in a network, the time
required for an accurate answer can be extremely large.
Specialized techniques such as "control variates" and
"importance sampling" have been developed to speed
simulation.
The network simulator must enable a user to:
1. Model the network topology specifying the nodes onthe
network and the links between those nodes
2. Model the application flow (traffic) between the nodes
3. Providing network performance metrics as output
4. Visualization of the packet flow
5. Logging of packet / events for drill down analyses or
debugging
The “ns-3” simulation software is built
using C++ and Python with scripting capability. The ns-3
library is wrapped by Pythonthanks tothepybindgenlibrary
which delegates the parsing of the ns-3 C++ headers to
gccxml and pygccxml to automatically generate the
corresponding C++ binding glue. These automatically-
generated C++ files are finally compiled into the ns-3 Python
module to allow users to interact with the C++ ns-3 models
and core through Python scripts. The ns-3 simulatorfeatures
an integrated attribute-based system to manage default and
per-instance values for simulation parameters. All of the
configurable default values for parameters are managed by
this system, integrated with command-line argument
processing. The large majorityofitsusersfocusesonwireless
simulations which involve models for Wi-Fi.
3.3 Network topology
The general process of creating a simulation can be divided
into several steps:
1. Topology definition: to ease the creation of basic
facilities and define their interrelationships, ns-3
has a system of containers and helpers that
facilitates this process.
2. Model development:modelsareaddedtosimulation
(forexample, UDP, IPv4, point-to-point devices and
links, applications); most of the time this is done
using helpers.
3. Nodeandlinkconfiguration:modelssettheirdefault
values (for example, the size of packets sent by an
application or MTU of a point-to-pointlink);mostof
the time this is done using the attribute system.
4. Execution:simulationfacilitiesgenerateevents,data
requested by the user is logged.
5. Performance analysis: after the simulation is
finished and data is available as a time-stamped
event trace. This data can then be statistically
analysed with tools like R to draw conclusions.
6. Graphical Visualization: raw or processed data
collected in a simulation can be graphed using tools
like Gnuplot, matplotlib or XGRAPH.
The selection of a network topology can affect:
1. Type of equipment the network needs.
2. Capabilities of the equipment.
3. Growth of the network.
4. Way the network is managed.
Standard Topologies:
1. Bus – Devices connected to acommon,shared cable.
2. Star - Connecting computers to cable segments
branch out from a single point, or hub.
3. Ring - Connecting computers to cable that form a
loop.
4. Mesh – Connects all computers in a network to each
other with separate cables.
Fig-3: Common network topologies
Fig-4: Network topology used

Fig-5: Network topology used
3.4 Observations
Experimental results (simulation) in the IPv4 network
protocol uses RIPv2 and OSPFv2 by using two different
simulators is GNS3. The result that the speed OSPFv2 router
for inter-router converge better than RIPv2 routers in the
experiment with GNS3. In experiments with GNS3 time from
R converge on IP 192.168.5.2 which uses OSPFv2 router,
round-trip min / avg / max = 996/1142/1200 ms, and the
process of tracing the route from R5 to R1 which is headedto
the IP 192.168. 1.1 through 192.168.6.2 takes 1060 msec
while through the IP192.168.5.2takes340msecandthrough
IP 192.168.2.2 takes 1768 msec.
For RIPv2 routers show round-trip min / avg / max =
924/1292/1440 and processes tracing the route from R1 to
R5 is heading to IP 192.168.1.1 through 192.168.6.2 takes
1460 msec while through the IP 192.168.5.2 takes 884 msec
and through IP 192.168.2.2 takes 1972 msec. RIP multicast
method takes a long time in terms of packet delivery.
3.5 Inferences
From the description and comparisonofperformanceaswell
as the experimental results OSPFv2 Routing Protocol (OPEN
Shortest Path First version 2) and RIPv2 (Routing
Information Protocol version 2) in the IPv4 network, then it
can be concluded that:
Every router within the samerouting protocolsbuildrouting
tables, based on information from neighboring routers for
sharing information between routers. Based on the speed of
delivery of the package with the parameter used is the time
between networks that converge OSPFv2 routing protocols
rather than RIPv2 better use RIPv2 using distance / hops
while for OSPF will use the same area thus saving bandwidth
usage. ENSP Simulator GNS3 looks faster than the time
required forinter-network converge. To wider networkthen
it would be better to use Dijkstraroutersbecauseofitsability
to divide the network area into several sections.
REFERENCES
[1] Setiawati L. Differences PerformanceOSPFv2andRIPv2
Routing Protocols In Network IPv4 Using Simulator
GNS3 And ENSP.
[2] Wu, B. (2011). Simulation Based Performance Analyses
on RIPv2, EIGRP, and OSPF Using OPNET.
[3] Youssef, M., Younis, M. F., & Arisha, K. (2002, March). A
constrained shortest-path energy-aware routing
algorithm for wireless sensor networks. In Wireless
Communications and Networking Conference, 2002.
WCNC2002. 2002 IEEE(Vol. 2, pp. 794-799). IEEE.
[4] Liu, L., Jin, J., Palaniswami, M., Liu, M., Li, X., & Huang, Z.
(2012). Graph-Based Routing, Broadcasting and
Organizing Algorithms for Ad-Hoc Networks. INTECH
Open Access Publisher.
[5] Kassabalidis, I., Das, A. K., El-Sharkawi, M. A., Marks II,R.
J., Arabshahi, P., & Gray, A. (2001, August). Intelligent
routing and bandwidth allocation in wireless networks.
In Proc. NASA Earth Science Technology Conf. College
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Minimum Hop Energy Efficient Routing
Protocol. International Journal of Computer
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PRZEGLAD ELEKTROTECHNICZNY, 88(8), 224-231.

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