CSE 550
Computer Network Design
Dr. Mohammed H. Sqalli
COE, KFUPM
Spring 2008 (Term 072)
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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Generations of Networking
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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 in use
today 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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Structured Network Design Process
- A Systems Approach (1/2)  The system is designed in a top-down sequence
 Several techniques and models can be used to
characterize the existing system, new user
requirements, and a structure for the future system
 A focus is placed on understanding:


Data flow, data types, and processes that access or
change the data
The location and needs of user communities that
access or change data and processes
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Structured Network Design Process
- A Systems Approach (2/2)  A logical model is developed before the physical
model


The logical model represents the basic building blocks,
divided by function, and the structure of the system
The physical model represents devices and specific
technologies and implementations
 For large network design projects, modularity is
essential

The design should be split functionally to make the
project more manageable
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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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