Requirements Capture and Specification

IACT424/924 Corporate Network Design and

Implementation

Overview

Network Services Requirements Analysis

Network Requirements User Requirements Application Requirements Host Requirements

Determining New Customer Requirements

Definition

Requirement 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

Sets of network capabilities that can be configured and managed within the network 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

Services need to be Configurable Measurable Verifiable

Ensure end users are getting the services they what they requested Accounting

Network Services

Services are generally hierarchical General services in the backbone Specific services close to users

Network services are derived from the requirements of all entities within the network They describe what is expected

by/from each entity

Network Services

Network service requirements include User requirements Application requirements Host requirements Network requirements

Network Services

Service offerings need to be configured end-to-end 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

Mismatches in services can result in network bottlenecks

Eth

erne

t

Eth

erne

t

FWT1

1.5 Mb/s

200 kb/s

10 Mb/s10 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 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

Requirements Analysis

Payoffs include 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

Host Host

Network

Network Requirements

This view is not complete enough for today’s networks Users and applications need to be

considered

User

Application

Host Network

User

Application

Host

User Requirements

Users generally have the following requirements Timeliness Interactivity Reliability Quality Adaptability Security Affordability

User Requirements

We also need to know how many users are expected to use the system and their locations

Application Requirements

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

Mission Critical Specified reliability

Controlled-Rate Specified capacity

Real-Time Specified delay

User vs Application Requirements

User Service Requirement Timeliness Interactivity Reliability Quality Adaptability Security Affordability User numbers User locations Expected growth

Performance Requirement

Delay

Reliability

Capacity

Host Requirements

Types of hosts and equipment Generic computing devices

Desktop PC’s Interface between application and network

Servers Provide service to one or more users Impact on information flow

Specialised equipment Supercomputers, mainframe, data gathering

equipment Location Dependant

Host Requirements

Performance characteristics include Storage performance Processor performance Memory performance (access times) Bus performance

Determining New Customer Requirements

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

Identify business constraints Document budget and available

resources Document project timeline Identify staffing requirements such as

training or hiring

Determining New Customer Requirements

Identify security requirements 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

Corporate branch offices Mobile users Telecommuters

Determining New Customer Requirements

Identify security requirements 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

Determining New Customer Requirements

Identify manageability requirements Fault Accounting Configuration Performance Security

Determining New Customer Requirements

Determine application requirements 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

Characterise new network traffic Characterise traffic load Characterise traffic behaviour

including Broadcast/multicast behaviour Frame size(s) supported Windowing and Flow control Error recovery mechanisms

Characterising Traffic Loads and Behaviour

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

Identify performance requirements Response time Accuracy Availability Maximum network utilisation Throughput Efficiency Latency

Determining New Customer Requirements

Create a customer needs specification document Record

The customers requirements and constraints

Characteristics of the existing network

References

Teare, D. 1999, Designing Cisco Networks, Cisco Press Indianapolis

McCabe, J. 1998, Practical Computer Network Analysis and Design, Morgan Kaufman, San Francisco