Network Design and Modeling

1. Chapter – I
Introduction to Network Design,
Modeling and Simulation
1

2. Network Design
• Network design is a category of system design that
deals with data transport mechanisms.
• As with other systems design disciplines,
• network design follows an analysis stage, where
requirements are generated, and precedes
implementation, where the system (or relevant
system component) is constructed.
2

3. Network Design Objective
• Ultimately, our network design must answer some
pretty basic questions
– What stuff do we get for the network?
– How do we connect it all?
– How do we have to configure it to work right?
• Traditionally this meant mostly
• Capacity planning – having enough bandwidth to
keep data moving
– May be effective, but result in over engineering
3

4. Network Design Objective
• While some uses of the network will need a lot of
bandwidth (multimedia), we may also need to
address:
– Security
• Considering both internal and external threats
– Possible wireless connectivity
– Reliability and/or availability
• Like speed for a car, how much are you willing
to afford?
4

5. Network Design Phases
• Designing a network is
typically broken into three
sections:
– Determine requirements
– Define the overall architecture
– Choose technology and specific
devices
5
(McCabe, 2003)

6. Network Design Methodology
• There’s lots of room for refining these sections
(Teare, 2004)
– Identify customer requirements
– Characterize the existing network
– Design topology
– Plan the implementation
– Build a pilot network
– Document the design
– Implement the design, and monitor its use
6

7. Two Main Principles
7

8. Two Main Principles
• For a network design to work well, we need to
balance between
– Hierarchy – how much network traffic flows connect in
tiers of organization
• Like tiers on an organization chart, hierarchy provides
separation and structure for the network
– Interconnectivity – offsets hierarchy by allowing
connections between levels of the design, often
to improve performance between them
8

9. Key characteristics that Affect post
implementation cost
• Network and system Reliability
• Network and system Maintainability
• Training of the operators to stay within
operational constraints
• Quality of the staff required for maintenance
actions
9

10. 1.1.2 Design Considerations of
Cellular, Radio and Transmission
Networks
10

11. 1G
(<1Kbps)
1 Kbps
10 Kbps
100 Kbps
2 Mbps
1 Mbps
Data Rates
1980 1990 2000 2010
2G
(9.6Kbps)
2.5G
(10-150Kbps)
3G
(144Kbps to 2Mbps)
Years
Overview
11

12. Cellular networks: From 1G to 3G
• 1G: First generation wireless cellular: Early 1980s
– Analog transmission, primarily speech: AMPS (Advanced Mobile Phone
Systems)
• 2G: Second generation wireless cellular: Late 1980s
– Digital transmission
– Primarily speech and low bit-rate data (9.6 Kbps)
– High-tier: GSM, CDMA
– Low-tier (PCS): Low-cost, low-power, low-mobility
• 2.5G: 2G evolved to medium rate (< 100kbps) data
• 3G: Broadband multimedia
– 144 kbps - 384 kbps for high-mobility, high coverage
– 2 Mbps for low-mobility and low coverage
12

13. A Cellular Network
Public
Switched
Telephone
Network
(PSTN)
Mobile
Telephone
Switching
Center
(MTSC)
Base Transceiver Station (BTS)
Mobile User
Cell 1
Cell 2
Cordless connection
Wired connection
HLR VLR
HLR = Home Location Register
VLR = Visitor Location Register
13

14. Cellular System
Handoffs (typically 30 mseconds):
1. At any time, mobile station (MS) is in one cell and under the control of a BS
2. When a MS leaves a cell, BS notices weak signal
3. BS asks surrounding BSs if they are getting a stronger signal
4. BS transfers ownership to one with strongest signal
5. MTSC assigns new channel to the MS and notifies MS of new boss
Public
Switched
Telephone
Network
(PSTN)
Mobile
Telephone
Switching
Center
(MTSC)
Cell 1
Cell 2
HLR VLR
14

15. E
A
D
F
G C
B
E
A
D
F
G C
B
E
A
D
F
G C
B
Cell Design
•Cells grouped into a cluster of seven
•Letters indicate frequency use
•For each frequency, a buffer of two cells is used before reuse
•To add more users, smaller cells (microcells) are used
•Frequencies may not need to be different in CDMA (soft handoff)
15

16. Cellular Network Organization
• Cell design (around 10 mile radius)
– Served by base station consisting of transmitter, receiver, and
control unit
– Base station (BS) antenna is placed in high places
(churches, high rise buildings) -
• Operators pay around $500 per month for BS
– 10 to 50 frequencies assigned to each cell
– Cells set up such that antennas of all neighbors are equidistant
(hexagonal pattern)
• In North America, two 25-MHz bands allocated to AMPS
– One for transmission from base to mobile unit
– One for transmission from mobile unit to base
16

17. Approaches to Increase Capacity
• Adding/reassigning channels - some channels are
not used
• Frequency borrowing – frequencies are taken
from adjacent cells by congested cells
• Cell splitting – cells in areas of high usage can be
split into smaller cells
• Microcells – antennas move to buildings, hills,
and lamp posts
17

18. 1.1.3. Design Models of Data Networks
18
Networking is a complicated task.
To ease network engineering, the whole networking concept
is divided into multiple layers.
The different classification of network into layers using
different standards is referred to as Modelling.

19. Layered tasks
In layered architecture of Network Models, one
whole network process is divided into small tasks.
Each small task is then assigned to a particular
layer which works dedicatedly to process the task
only.
Every layer does only specific work.
In layered communication system, one layer of a
host deals with the task done by or to be done by its
peer layer at the same level on the remote host.
19

20. Basic Network Models
Different network models exists.
But,
In this , the two different internationally accepted
network models
 The OSI model
The internet model
20

21. The OSI Model
The Open System Interconnect (OSI) model is an
open standard for all communication systems. OSI
model is established by International Standard
Organization. This model has seven layers:
Figure 2: The OSI Network Model
21

22. OSI model contd.
Application Layer: This layer is responsible for providing interface
to the application user. This layer includes protocols which directly
interacts with the user.
Presentation Layer: This layer defines how data in the native
format of remote host should be presented in the native format of
host.
Session Layer: This layer maintains sessions between remote
hosts.
For example, once user/password authentication is done, the
remote host maintains this session for a while and does not ask for
authentication again in that time span.
22

23. OSI model contd.
Transport Layer: This layer is responsible for end-to-end
delivery between hosts.
Network Layer: This layer is responsible for address
assignment and uniquely addressing hosts in a network.
Data Link Layer: This layer is responsible for reading and
writing data from and onto the line. Link errors are detected
at this layer.
Physical Layer: This layer defines the hardware, cabling
and wiring, power output, pulse rate etc.
23

24. The Internet Model
Internet uses TCP/IP protocol suite, also known as Internet suite using a four layered
architecture
 Application Layer: Defines the protocol which
enables user’s access to the internet using protocols
like FTP, HTTP etc.
 Transport Layer: Defines how data should flow
between hosts. The major protocol at this layer is TCP
(Transmission Control Protocol).
 Internet Layer: IP works on this layer. This layer
facilitates host addressing, recognition and routing.
 Link Layer: Provides mechanism of sending and
receiving actual data. layer is independent of
underlying network architecture and hardware.
Figure 3: The Internet Model
24

25. Networks types
The basic types of computer networks include;
LAN (Local Area Network),
MAN (Metropolitan Area Network)
CAN (Campus Area Network)
WAN (Wide Area Network)
25

26. Example of a Typical Enterprise Network
Comprise of LANs, CANs, and LANs
Figure 4: A Typical Enterprise Network
26

27. Star Network Design Model
The traditional star topology typically meets the needs of a small
company as it first expands to new locations.
A single router, located at the company’s headquarters, interconnects
all the sites.
Figure 5: The Star Network Design Model
27

28. The star model contd.
The following list encompasses both the positive and negative
aspects of such a topology, but the negative aspects should be
somewhat obvious:
• Low scalability
• Single point of failure
• Low cost
• Easy setup and administration
The entire network will likely mesh into another model, though the
remote portion of the network will use the star topology.
The star topology is also called the hub-and-spoke model.
28

29. The Ring Network Model
• The ring topology builds upon the star topology with a few significant
modifications.
• This design is typically used when a small company expands nationally
and two sites are located close together.
• The design improves upon the star topology
Figure 6: The Ring Network Design Model
29

30. Ring model contd.
Eliminates single circuit failure will not disconnect any location from
the enterprise network.
But,
The ring topology fails to address these other considerations:
Low scalability
No single point of failure
Higher cost
Complex setup and configuration
Difficulty incorporating new locations (See fig in the next slide)
30

31. Adding a new location in a Ring
topology
Location A Location B
Location D
Location C
Location E (New Location)
Circuit
Location A Location B
Router
Location D
Location C
Figure 8: The Ring Model with four locations
Figure 9: Adding a new location in a Ring Model with four locations
31

32. The Mesh Network Model
Equation N(N-1) /2
6(6-1) /2
6(5) /2
30 / 2
15 Connections
(Reed’s Law)
Fully Meshed Topology
PVC
Figure 10: A Full Mesh Network Design Model
32

33. Benefits of the Mesh topology
The full-mesh topology offers the network designer many
benefits like;
Redundancy
Scalability
However,
The full-mesh network will also require a great deal of financial
support.
Scalability problems as the number of PVCs increases
33

34. Partial Mesh
The partial-mesh model does not constrain the designer with a predefined number
of circuits per nodes in the network, which permits some latitude in locating and
provisioning circuits.
However, this flexibility can cause reliability and performance problems.
The benefit is cost because, fewer circuits can support the entire enterprise while
providing specific data paths for higher priority connections.
34

35. Two tier network model
The two-tier model shares many attributes with the partial-mesh
model
The difference is the design’s additional benefits.
This design is often born as a result of merging two companies and
each of them small in size and already using historical star topologies
Model’s Advantage
◦ reduces total costs yet provides some redundancy.
35

36. Two tier contd.
Location A
Circuit
Location B
Location E
Location C Location D Location F
The two tier works best when locations A and B have strong support
organizations and the expenses associated with complete integration
are high.
Also if there is a limited connectivity between the two primary sites and
the lack of any other connections
Access layer
Collapsed Distribution
and Core
Figure 11: The two Tier Network Design Model
36

37. The Hierarchical Network Design Model.
This model present three layers as shown in the diagram above
Figure 11: The Three Tier Network Design Model
37

38. Benefits of the 3 tier model
The biggest advantage to this design is scalability.
This model is particularly valuable when using hierarchical routing
protocols and summarization, specifically OSPF (Open Shortest Path First).
Reducing the impact of failures and changes in the network.
Simplifies implementation and troubleshooting, in addition to
contributing to predictability and manageability
These benefits greatly augment the functionality of a network and the
appropriateness of the model to address network design goals.
38

39. Network Planning And Design
Planning and Designing a network can be a challenging task.
It is aimed at achieving
A reliable network
A scalable networks
Ensuring that network meets the needs of the subscriber
39

40. Network Planning Methodology
A traditional network planning methodology involves five layers of
planning, namely:
1. Business planning: determines the planning that the operator
must perform to ensure that the network will perform as
required for its intended life-span.
2. Long-term and medium-term network planning
3. Short-term network planning
4. IT asset sourcing
5. Operations and maintenance: The Operations and Maintenance
layer, however, examines how the network will run on a day-to-
day basis.
40

41. Network Planning
Network planning process begins with the acquisition of external information
that include the following;
◦ forecasts of how the network will operate
◦ The costs implication
◦ The technical details of the network’s capabilities.
This involves three main stages which are;
◦ Topology design
◦ Network-synthesis
◦ Network Realization.
41

42. Forecasting
In the process of Network Planning and Design, the expected traffic
intensity and traffic load that the network must support are estimated.
The forecasting process involves several steps;
Definition of problem;
Data acquisition;
Choice of forecasting method;
Analysis/Forecasting;
Documentation and analysis of results.
42

43. Introduction To Modeling and
Simulation
43

44. Solving using Simulation
Actual Problem
Modeling
Simulation
Results

45. A simulation:
 A simulation is the imitation of the
operation of real-world process or system
over time.
 A Representation of an object, a system, or
an idea in some form other than that of the
entity itself.
45

46. A model:
46
 A model construct a conceptual framework
that describes a system
 The behavior of a system that evolves over
time is studied by developing a simulation
model.

47. Goal of modeling and simulation
 A model can be used to investigate a wide verity of
“what if” questions about real-world system.
 Potential changes to the system can be simulated and predicate their
impact on the system.
 Find adequate parameters before implementation
• So simulation can be used as
 Analysis tool for predicating the effect of changes
 Design tool to predicate the performance of new system
• It is better to do simulation before Implementation.
47

48. When Simulation Is the Appropriate Tool
 Simulation enable the study of internal interaction of
a subsystem with complex system
 Informational, organizational and environmental
changes can be simulated and find their effects
 A simulation model help us to gain knowledge about
improvement of system
 Finding important input parameters with changing
simulation inputs
 Simulation can be used with new design and policies
before implementation
48

49. When Simulation Is the Appropriate Tool
 Simulating different capabilities for a machine can
help determine the requirement
 Simulation models designed for training make
learning possible without the cost disruption
 A plan can be visualized with animated simulation
 The modern system (factory, service organization) is
too complex that its internal interaction can be
treated only by simulation
49

50. When Simulation Is Not Appropriate
 When the problem can be solved by common sense.
 When the problem can be solved analytically.
 If it is easier to perform direct experiments.
 If cost exceed savings.
 If resource or time are not available.
 If system behavior is too complex.
 Like human behavior
50

51. Advantages of simulation
 New policies, operating procedures, information
flows can be explored without disrupting ongoing
operation of the real system.
 New hardware designs, physical layouts,
transportation systems can be tested without
committing resources for their acquisition.
 Time can be compressed or expanded to allow for a
speed-up or slow-down of the phenomenon( clock is
self-control).
51

52. Advantages of simulation
 Insight can be obtained about interaction of
variables and important variables to the
performance.
 Bottleneck analysis can be performed to discover
where work in process, the system is delayed.
 A simulation study can help in understanding how
the system operates.
 “What if” questions can be answered.
52

53. Disadvantages of simulation
 Model building requires special training.
 Vendors of simulation software have been actively developing
packages that contain models that only need input (templates).
 Simulation results can be difficult to interpret.
 Simulation modeling and analysis can be time
consuming and expensive.
 Many simulation software have output-analysis.
53

54. Areas of application
 Manufacturing Applications
 Semiconductor Manufacturing
 Construction Engineering and project management
 Military application
 Logistics, Supply chain and distribution application
 Transportation modes and Traffic
 Business Process Simulation
54

55. 1.2. Overview of Modeling and
Simulation Tools
55

56. The ONE
• The Opportunistic Network Environment simulator.
Information
• The ONE is a simulation environment that is capable of
generating node movement using different movement models
• routing messages between nodes with various DTN routing
algorithms and sender and receiver types
• visualizing both mobility and message passing in real time in its
graphical user interface.
• ONE can import mobility data from real-world traces or other
mobility generators.
• It can also produce a variety of reports from node movement
to message passing and general statistics.
56

57. What is NS2
• NS2 stands for Network Simulator Version
• It is an open-source event-driven simulator
designed specifically for research in computer
communication networks.
57

58. 2. Features of NS2
1. It is a discrete event simulator for networking
research.
2. It provides substantial support to simulate bunch
of protocols like TCP, FTP, UDP, https .
3. It simulates wired and wireless network.
4. It is primarily Unix based.
5. Uses TCL as its scripting language.
6. Otcl: Object oriented support
7. Discrete event scheduler
58

59. 3. Basic Architecture
• NS2 consists of two key languages: C++ and
Object-oriented Tool Command Language (OTcl).
• While the C++ defines the internal mechanism
(i.e., a backend) of the simulation objects, the
OTcl sets up simulation by assembling and
configuring the objects as well as scheduling
discrete events.
• The C++ and the OTcl are linked together using
TclCL
59

60. 4. Why two language? (TCL and
C++)
• NS2 stands for Network Simulator Version 2.
• It is an open-source event-driven simulator
designed specifically for research in computer
communication networks.
• NS2 uses OTcl to create and configure a network,
and uses C++ to run simulation.
• All C++ codes need to be compiled and linked to
create an executable file.
60

61. OPNET
 OPNET stands for Optimum Network
Performance
 Opnet is a network simulation tool
 Opnet Modeler, in particular, is a research
oriented package.

62. Modeling
 Graphical User Interface
 Hierarchical Modeling
 Network
 Node
 Process

63. Editors
 Network Editor
 Node Editor
 Process Editor
 Packet Editor
 Link Editor
 etc....

64. Network Model
 Rapid Configuration Wizards
 Step by step fill in basic data
 Create your Own
 Object Palettes to help you
 Subnets
 Wired
 Mobile
 Satellite

65. Example Network Model

66. Example Object Palette

67. Node Model
 Generic devices provided
 Vendor devices provided
 Create your own devices (models)
using,
 Processor
 Queue
 Interfaces

68. Example Node Model

69. Process Model
 A State Transition Diagram
 States
 Forced
 Unforced
 Transitions
 Conditions

70. Simulation
 Select Duration, Seed, other Attributes
 Run the Simulation
 View Graphs produced
 Analyze

71. Introduction to OMNeT++

72. What is OMNeT++?
• OMNeT++ is a C++-based discrete event simulator
for modeling communication networks,
multiprocessors and other distributed systems.
• A new simulator for wireless sensor networks.
• Its results are very close to real world results.
• www.Omnetpp.org
72

73. Installing OMNeT++
To install OMNeT++:
1. Install Microsoft Visual C++.
2. Install OMNeT++ 3.3 (binary release) for
windows.
• OMNET++ version 4, released in November
2008.
73

74. 74

75. Simulation must have following files:
- omnetpp.ini
- Specify: network, simulation speed, output-scalar-file,
network area (x,y),number of nodes, other parameters,
- module. ned
- Defines the network and the modules in side it, and each
module ( its gates and other parameters).
- module.cc , module.h
- Define the functionality of each module, mainly include:
- initialize()
- handleMessage(cMessage * msg)
- finish()
OMNET++ Main Components
75

76. WSN Routing Algorithms
• Wireless Sensor Network- WSN: a collection of a large
number of sensors without the support of pre-existing
infrastructure, distributed to be close to the phenomena being
monitored.
• WSN main drawback is limited energy supported in sensors.
(limited rechargeable, un-replaceable batteries)
• Main factor of energy consumption is communication:
Transmitting, Receiving (consumes less).
• Routing algorithms control communication.
76

77. WSN Routing Algorithms
• Cluster based routing algorithms: routing
algorithms based on the idea of creating clusters to
collect the data and route it from the sensors to the
sink (BS).
• It is efficient because it:
1. Reduces energy consumption within the cluster,
2. Performs data aggregation, which:
reduces the amount of data.
reduces the number of packets to send to the
sink.
77

78. WSN Routing Algorithms
LEACH - Low Energy Adaptive Clustering Hierarchy
PEGASIS - Power–Efficient Gathering in Sensor Information
System
78

79. LEACH
Advantages:
• Energy savings due to combining lossy compression with
the data routing.
• It distributes energy-usage among the nodes; nodes die
randomly and at the same rate.
Disadvantage
• Doesn’t ensure that CH’s are uniformly placed across the
whole sensor field,
• CH’s transmit data directly to the distant BS, while
members sends to a close CH.
79

80. PEGASIS
Advantages:
• Saving energy by minimizing:
• The transmission distance
• The number of transmissions and receives for each node
• Each node will be the leader once every 100 rounds (for 100
nodes network).
Disadvantages
• Main: long chain and the very high delay probability;
• Nodes may have distant neighbours along the chain.
• Increasing neighbour distances will have a significant effect on
PEGASIS performance
80

81. Resources
- OMNeT++ Folder
- Documentation
- Tutorial
- Samples
- OMNeT++ website: omnetpp.org
- Other WSN simulators: Castalia, NesCT, Jsim, NS2.
81

82. • http://one-simuator-for-
beginners.blogspot.com/2013/08/one-
simulator-introduction.html
82

83. NS2
• https://www.tutorialsweb.com/ns2/index.htm
• https://ns2projects.org/ns2-tutorial-for-
beginners/
• https://www.ns2project.com/ns2-tutorial-for-
beginners/
• https://ns2blogger.blogspot.com/p/for-ns2-
beginners.html
83

84. References
• http://opnet.com/products/modeler/
• Opnet Modeler Manual
• Opnet Online Tutorial
• Notes from Dr. Osborne (Summer 2002)