requirements capture and specification iact424/924 corporate network design and implementation
Post on 20-Dec-2015
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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