Transcript Requirements Capture and Specification IACT424/924 Corporate Network Design and Implementation

Requirements Capture and
Specification
IACT424/924 Corporate Network
Design and Implementation
Overview
Network Services
 Requirements Analysis
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Network Requirements
User Requirements
Application Requirements
Host Requirements
Determining New Customer
Requirements
Definition
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Requirement
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That which is required or needed; a want,
need
That which is called for or demanded; a
condition which must be complied with.
Network Services
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Sets of network capabilities that can be
configured and managed within the
network
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Levels of performance and function offered
Sets of requirements expected
For services to be useful and effective
they need to be provisioned end-to-end
Network Services
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Services need to be
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Configurable
Measurable
Verifiable
Ensure end users are getting the
services they what they requested
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Accounting
Network Services
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Services are generally hierarchical
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General services in the backbone
Specific services close to users
Network services are derived from the
requirements of all entities within the
network
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They describe what is expected by/from
each entity
Network Services
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Network service requirements include
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User requirements
Application requirements
Host requirements
Network requirements
Network Services
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Service offerings need to be configured
end-to-end
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Requirements add to each other filtering
from user to network
In addition to providing performance
and function to users they support
design and operation of the network
Network Services
T1
FW
1.5 Mb/s
10 Mb/s
200 kb/s
Ethernet
Mismatches in services can result in
network bottlenecks
Ethernet
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10 Mb/s
Requirements Analysis
The identification of bottlenecks like this
is one of the primary goals of network
design
 After identifying service requirements
the next stage is to quantify what we
want from the network
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To do this we need to analyse and define
the requirements of the network
Requirements Analysis
Without adequate requirement analysis
networks tend to be designed on
factors other than users needs
 Requirement analysis assists in
understanding the probable behaviour
of the network
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Requirements Analysis
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Payoffs include
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Objective, informed choices of technologies
and services
Match of interconnection strategies to
networks
Networks and components that are
properly sized to users and applications
Better understanding of of where and how
to apply services in the network
Network Requirements
Network designers have traditionally
focused on providing connectivity
between hosts
 Typically users and applications were
not considered
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Host
Host
Network
Network Requirements
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This view is not complete enough for
today’s networks
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Users and applications need to be
considered
User
User
Application
Application
Host
Network
Host
User Requirements
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Users generally have the following
requirements
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Timeliness
Interactivity
Reliability
Quality
Adaptability
Security
Affordability
User Requirements
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We also need to know how many users
are expected to use the system and
their locations
Application Requirements
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Whilst many applications are still ‘best-effort’
users requirements and performance
requirements (delay, capacity, reliability) are
now being emphasized
These requirements lead to a distinction
between application that need specific service
levels and those that don’t
Descriptions of performance requirements for
applications will separate specified services
from best effort
Types of Specified Service
applications
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Mission Critical
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Controlled-Rate
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Specified reliability
Specified capacity
Real-Time
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Specified delay
User vs Application
Requirements
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User Service Requirement
 Timeliness
 Interactivity
 Reliability
 Quality
 Adaptability
 Security
 Affordability
 User numbers
 User locations
 Expected growth
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Performance Requirement
Delay
Reliability
Capacity
Host Requirements
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Types of hosts and equipment
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Generic computing devices
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Servers
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Desktop PC’s
Interface between application and network
Provide service to one or more users
Impact on information flow
Specialised equipment
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Supercomputers, mainframe, data gathering equipment
Location Dependant
Host Requirements
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Performance characteristics include
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Storage performance
Processor performance
Memory performance (access times)
Bus performance
Determining New Customer
Requirements
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Identify business constraints
Identify security requirements
Identify manageability requirements
Determine application requirements
Characterise new network traffic
Identify performance requirements
Create a customer needs specification
document
Determining New Customer
Requirements
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Identify business constraints
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Document budget and available resources
Document project timeline
Identify staffing requirements such as
training or hiring
Determining New Customer
Requirements
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Identify security requirements
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Appraise security risks and determine how much
security will be needed and of what type
Determine requirements for for outsiders to access
data
Determine the authorisation and authentication
requirements for
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Corporate branch offices
Mobile users
Telecommuters
Determining New Customer
Requirements
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Identify security requirements
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Identify requirements for authenticating
routes received from access routers or
other routers
Identify requirements for host security
Physical security of hosts
 User accounts
 Dated software
 Access rights on data
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Determining New Customer
Requirements
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Identify manageability requirements
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Fault
Accounting
Configuration
Performance
Security
Determining New Customer
Requirements
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Determine application requirements
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Document names and types of new applications
Document names and types of new protocols
Document the number of users who will be using
new applications and protocols
Diagram the flow of information when new
applications are introduced
Identify peak hours of usage for new applications
Determining New Customer
Requirements
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Characterise new network traffic
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Characterise traffic load
Characterise traffic behaviour including
Broadcast/multicast behaviour
 Frame size(s) supported
 Windowing and Flow control
 Error recovery mechanisms
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Characterising Traffic Loads
and Behaviour
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Approximate sizes of “objects”
transferred across networks
Type of Object
Size (MB)
E-Mail message
0.01
Spreadsheet
0.1
Document
1
Still image
10
Multimedia
Object
100
Database
1000
Determining New Customer
Requirements
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Identify performance requirements
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Response time
Accuracy
Availability
Maximum network utilisation
Throughput
Efficiency
Latency
Determining New Customer
Requirements
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Create a customer needs specification
document
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Record
The customers requirements and constraints
 Characteristics of the existing network
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References
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Teare, D. 1999, Designing Cisco Networks, Cisco
Press Indianapolis
McCabe, J. 1998, Practical Computer Network
Analysis and Design, Morgan Kaufman, San Francisco