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 Ethernet FW T1 1.5 Mb/s 200 kb/s 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 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 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 ObjectSize (MB) message0.01 Spreadsheet0.1 Document1 Still image10 Multimedia Object 100 Database1000

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