CSE 550
Computer Network Design
Dr. Mohammed H. Sqalli
COE, KFUPM
Spring 2012 (Term 112)
Introduction
 What is a Network?
 What is “Network Design”?
 Top-Down Network Design
 Network Development Life Cycle (NDLC)
 Network Analysis and Design Methodology
 Types of Network Design
 And Then What?
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What is a Network?
 Management view
 Technical view
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The Management View (1/3)
 A network is a utility
 Computers and their users are customers of the network
utility
 The network must accommodate the needs of
customers

As computer usage increases so does the requirements
of the network utility
 Resources will be used to manage the network
 The Network Utility is NOT free!
 Someone must pay the cost of installing and maintaining
the network
 Manpower is required to support the network utility
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The Management View (2/3)
 Utilities don’t bring money into the organization
 Expense item to the Corporation
 Cannot justify Network based on “Productivity
Improvements”
 As a network designer, you need to explain to
management how the network design, even with the
high expense, can save money or improve the
company’s business


If users cannot log on to your commerce site, they will try
your competitor, and you have lost sales
If you cannot get the information your customers are
asking about due to a network that is down, they may go
to your competitor
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The Management View (3/3)
 You need to understand how the network assists the
company in making money and play on that strength
when you are developing the network design proposal
 Try to show a direct correlation between the network
design project and the company’s business

“Because you want a faster network” is not good enough,
the question that management sends back is WHY DO I
NEED A FASTER ONE?
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The Technical View (1/2)
 A “Network” really can be thought of as three parts and they
all need to be considered when working on a network design
project:



Connections
Communications/Protocols
Services
 Connections
 Provided by Hardware that ties things together
 Wire/Fiber/Wireless Transport Mechanisms
 Routers
 Switches/Hubs
 Computers
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The Technical View (2/2)
 Communications/Protocols
 Provided by Software
 A common language for 2 systems to communicate with each other




TCP/IP (Internet/Windows NT)
IPX / SPX (Novell Netware 4)
AppleTalk
Other Network OS
 Services
 The Heart of Networking
 Cooperation between 2 or more systems to perform some function Applications




telnet
FTP
HTTP
SMTP
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Traditional Network Design
 Based on a set of general rules
 “80/20”
 “Bridge when you can, route when you must”
 Can’t deal with scalability & complexity
 Focused on capacity planning
 Throw more bandwidth at the problem
 No consideration to delay optimization
 No guarantee of service quality
 Less importance given to network RMA (Reliability,
Maintainability, and Availability) compared to throughput
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Application Characteristics
Applications
Message
Length
Message
arrival rate
Delay need
Reliability
need
Interactive
terminals
Short
Low
Moderate
Very high
File transfer
Very long
Very low
Very low
Very high
Hi-resolution
graphics
Very long
Low to
moderate
High
Low
Packetized
voice
Very short
Very high
High
Low
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Application Bandwidths
Transaction
Processing
100 Bytes
Few Kbps
Word Processing
100s Kbps
Few Mbps
File Transfers
Few Mbps
10s Mbps
Real-Time Imaging
10s Mbps
100s Mbps
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A Look on Multimedia Networking
Video standard
Bandwidth per
user
WAN services
Digital video
interactive
1.2 Mbps
DS1 lines ISDN
H11, Frame
Relay, ATM
Motion JPEG
10 to 240 Mbps
ATM 155 or 622
Mbps
MPEG-1
1.5 Mbps
DS1 lines ISDN
H11, Frame
Relay, ATM
MPEG-2
4~6 Mbps
DS2, DS3, ATM
at DS3 rate
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Some Networking Issues








LAN, MAN and WAN
Switching and routing
Technologies: Ethernet, FDDI, ATM …
Wireless/Mobile networking
Internetworking
Applications
Service quality
Security concerns
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Network Design: Achievable?
Response Time
Cost
Business Growth
Reliability
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Where to begin?
Traffic
WWW
Addressing
Patterns
Access
Campus
Security
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Users
WAN
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Dial in
Users
Network
Management
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Traditional Network Design Methodology
 Many network design tools and methodologies that
have been used resemble the “connect-the-dots”
game
 These tools let you place internetworking devices on
a palette and connect them with LAN or WAN media
 Problem with this methodology:
 It skips the steps of analyzing a customer's
requirements, and selecting devices and media based
on those requirements
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Top-Down Network Design Methodology (1/2)
 Good network design
 Recognizes that a customer’s requirements embody
many business and technical goals
 May specify a required level of network performance,
i.e., service level
 Includes difficult network design choices and tradeoffs
that must be made when designing the logical network
before any physical devices or media are selected
 When a customer expects a quick response to a
network design request

A bottom-up (connect-the-dots) network design
methodology can be used, if the customer’s
applications and goals are well known
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Top-Down Network Design Methodology (2/2)
 Network designers often think they understand a
customer’s applications and requirements.
 However, after the network installation, they may
discover that:


They did not capture the customer's most important
needs
Unexpected scalability and performance problems
appear as the number of network users increases
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Top-Down Network Design Process (1/2)
 Begins at the upper layers of the OSI reference
model before moving to the lower layers

Focuses on applications, sessions, and data transport
before the selection of routers, switches, and media
that operate at the lower layers
 Explores divisional structures to find the people:
 For whom the network will provide services, and
 From whom to get valuable information to make the
design succeed
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Top-Down Network Design Process (2/2)
 It is an iterative process:
 It is important to first get an overall view of a
customer's requirements
 More detail can be gathered later on protocol behavior,
scalability requirements, technology preferences, etc.
 Recognizes that the logical model and the physical
design may change as more information is gathered
 A top-down approach lets a network designer get
“the big picture” first and then spiral downward into
detailed technical requirements and specifications
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Network Development Life Cycle
Analysis
Management
Design
Simulation/
Prototyping
Monitoring
Implementation
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Network Design and Implementation Cycle
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Network Design and Implementation Cycle (1/3)
 Analyze requirements:




Interviews with users and technical personnel
Understand business and technical goals for a
new or enhanced system
Characterize the existing network: logical and
physical topology, and network performance
Analyze current and future network traffic,
including traffic flow and load, protocol
behavior, and QoS requirements
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Network Design and Implementation Cycle (2/3)
 Develop the logical design:
 Deals with a logical topology for the new or
enhanced network
 Network layer addressing and naming
 Switching and routing protocols
 Security planning
 Network management design
 Initial investigation into which service
providers can meet WAN and remote access
requirements
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Network Design and Implementation Cycle (3/3)
 Develop the physical design:
 Specific technologies and products to realize the
logical design are selected
 The investigation into service providers must be
completed during this phase
 Test, optimize, and document the design:
 Write and implement a test plan
 Build a prototype or pilot
 Optimize the network design
 Document your work with a network design proposal
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Another Perspective
 Data collection
 Traffic
 Costs
 Constraints
 Design process
 Performance analysis
 Fine tuning
 A painstaking iterative process
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PDIOO Network Life Cycle (1/3)
(Cisco)
 Plan:



Network requirements are identified in this phase
Analysis of areas where the network will be installed
Identification of users who will require network services
 Design:

Accomplish the logical and physical design, according
to requirements gathered during the Plan phase
 Implement:


Network is built according to the Design specifications
Implementation also serves to verify the design
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PDIOO Network Life Cycle (2/3)
(Cisco)
 Operate:


Operation is the final test of the effectiveness of the design
The network is monitored during this phase for performance
problems and any faults, to provide input into the Optimize
phase
 Optimize:



Based on proactive network management which identifies
and resolves problems before network disruptions arise
The optimize phase may lead to a network redesign
 if too many problems arise due to design errors, or
 as network performance degrades over time as actual
use and capabilities diverge
Redesign may also be required when requirements change
significantly
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PDIOO Network Life Cycle (3/3)
(Cisco)
 Retire:


When the network, or a part of the network, is out-of-date, it
may be taken out of production
Although Retire is not incorporated into the name of the life
cycle (PDIOO), it is nonetheless an important phase
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One More Look
Business
Planning
Network
Design
Implement
Network
Operations
Define Objectives
and Requirements
Develop
Architecture
Create
Implementation Plan
Develop Operations
Policies and
Capabilities
Create Initial
Solution
Develop Detailed
Design
Procure Resources
and Facilities
Fault
Management
Define Deployment
Strategy
Create Build
Documentation
Stage and Install
Configuration
Management
Review and
Approve
Review and Verify
Design
Certify and Hand-off
to Operations
Change
Management
Performance
Management
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Information Flows between Network
Analysis, Architecture, and Design
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Network Analysis and Design Methodology
- Overall Characteristics  Requirements (business, application, and data)
definition is required prior to network design activities
 Expected compliance with requirements in a Request
For Proposal (RFP) by both in-house personnel and
outside consultants
 Activities from various stages often take place
simultaneously and backtrack to previous activities is
sometimes needed
 This methodology is an overall guideline to the
network development process rather than “cookbook”
instructions
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Network Analysis and Design Methodology
- Critical Success Factors of the NDLC (1/3)  Identification of all potential customers and
constituencies

All groups must be consulted
 Political awareness:



Corporate culture: hierarchical, distributed, or open
Backroom politics can play a role in systems design
Find ways to ensure objectivity of the analysis and design
process (e.g., measurable goals)
 Buy-in:



Reach consensus on the acceptability of results of each stage
Approved results of one stage become the foundation or
starting point for the next stage
Makes the final presentation smoother
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Network Analysis and Design Methodology
- Critical Success Factors of the NDLC (2/3)  Communication:
 With all groups
 Write memos, communicate with key people in person,
etc.
 Detailed project documentation:
 Prepare agendas
 Take meeting minutes
 Action items
 Use a project binder for all the above
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Network Analysis and Design Methodology
- Critical Success Factors of the NDLC (3/3)  Process/Product awareness:
 Stay focused: what is the process/product at each
stage?
 Keep meeting on track: no off-subject discussions
 Be honest with yourself:
 Be your own harshest critic (no one else knows the
potential weaknesses or areas for improvement in your
proposal better than you)
 Use peer reviews
 Not all weaknesses can be corrected (e.g., financial or
time constraints)
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Network Analysis and Design Methodology
- Overall Guidelines  Start with a clearly defined problem:
 Identify affected parties and representatives
 Held brainstorming sessions to define problems and
requirements of a solution
 Understand strategic business objectives defined by
senior management
 Collect baseline data from customer groups about
the current status of the system and network

This is used to measure eventual impact of the
installed network
 Perform a feasibility study: problem definition and
associated alternative recommendations for further
study
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Customer’s Requirements
- Understanding the Customer  A good network design must recognize the customer’s
requirements - need to make sure your design meets
THEIR needs and not just YOURS!
 The “Customer” may be your own firm, the “who” you are
designing the network for
 Need an overview of a customer’s requirements
 The best designed network will fail miserably without
the support of people
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Customer’s Requirements
- Users’ Needs  What do the users want?

Services
 What do the users need?
 What don’t they know but they need?
 Organize and Prioritize Requirement
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Customer’s Requirements
- How they are used  User Requirements 
Performance Requirements
• Timeliness
• Interactivity
• Reliability
• Quality
• Security
• Affordability
• User Numbers
• User Locations
• User Growth
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Delay
Reliability
Capacity
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Analysis and Design Processes
 Set and achieve goals
 Maximizing performance
 Minimizing cost
 Optimization with trade-offs
 Recognizing trade-offs
 No single ‘best’ answer
 Hierarchies
 Provide structure in the network
 Redundancy
 Provides availability & reliability
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Approaches Used for Design
 Heuristic – by using various algorithms
 Exact – by working out mathematical
solutions based on linear programming, etc.,
minimizing certain cost functions
 Simulation – often used when no exact
analytical form exists. Experiments are
conducted on simplified models to see the
performance of a network
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Design and Study of a System
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Art or Science?
The Art of Network Design
• Technology choices
• Relations to business goals
The Science of Network Design
Understanding of network technologies
Analysis of capacity, redundancy, delay …


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Types of Network Design
 New network design
 Re-engineering a network design
 Network expansion design
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New Network Design
 Actually starting from scratch
 No legacy networks to accommodate
 Major driver is the budget, no compatibility
issues to worry about
 Getting harder to find these situations
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Re-engineering a Network Design
 Modifications to an existing network to
compensate for original design problems
 Sometimes required when network users
change existing applications or functionality
 More of the type of problems seen today
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Network Expansion Design
 Network designs that expand network
capacity
 Technology upgrades
 Adding more users or networked equipment
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This Whole Thing is Messy
This Whole Thing is Messy
 Ambiguous Requirements

The network will only transport IP

The application requires Novell IPX
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This Whole Thing is Messy
 Conflicting Requirements

Keep costs down

High performance costs money
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This Whole Thing is Messy
 Lack of Design Tools
 Lack of Management Tools
 Lack of Vendor Interoperability
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This Whole Thing is Messy
 Lack of Documentation

Existing network

How things should be done (e.g., wiring)

Vendor information
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This Whole Thing is Messy
 Network Management

More management uses more bandwidth

Every vendor has their own management tools

Vendor tools may conflict with each other
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This Whole Thing is Messy
Security
 What is enough security?
 What is too much security?

Security and management can not be dealt
with as ‘afterthoughts’. It is not an add-on
feature, it has to be integrated within.
Firewall
200Kbs
10Mb/s
Ethernet
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10Mb/s
Ethernet
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This Whole Thing is Messy
 Evolving Network Technologies



Everything is a moving target
Products are put onto the market before
standards are approved
Everyone is a computer “expert”
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OAM&P
Operations, Administration, Maintenance, Provisioning
Network
Management
Network
Provisioning
Network
Operations
Network
Maintenance
Planning
Fault Management / Service Restoration
Fault Management
Design
Configuration Management
Trouble Ticket
Administration
Performance Management / Traffic Management
Network Installation
Security Management
Network Repairs
Accounting Management
Facilities Installation
Reports Management
& Maintenance
Routine Network
Inventory Management
Tests
Data Gathering & Analyses
Figure 1.21 Network Management Functional Groupings
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Functional Flow Chart
Network
Users
Configuration Data
Management
Decision
New
Technology
Performance & Traffic Data
Engineering Group
- Network Planning &
Design
TT Restoration
Operations Group
NOC
I & M Group
-Network Installation &
Maintenance
- Network Operations
Fault TT
Installation
Figure 1.22. Network Management Functional Flow Chart
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References






Dr. Khalid Salah (ICS, KFUPM), CSE 550 Lecture Slides, Term
032
Dr. Marwan Abu-Amara (COE, KFUPM), CSE 550 Lecture
Slides, Term 052
P. Oppenheimer, “Top-Down Network Design,” Cisco Press, 3rd
edition, 2010
J. McCabe, “Network Analysis, Architecture, and Design”
Morgan Kaufmann Publishers, Inc., 3rd edition, 2007
J. E. Goldman, “Applied Data Communications - A BusinessOriented Approach”, 1998
Mani Subramanian, “Network Management – Principles and
Practice” by, Pearson, Second Edition, 2010.
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