design requirements
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Design Requirements. IACT424/924 Corporate Network Design and Implementation. Review. Requirements Analysis Network Requirements User Requirements Application Requirements Host Requirements Determining New Customer Requirements. Overview. Gathering and Listing Requirements - PowerPoint PPT PresentationTRANSCRIPT
Design Requirements
IACT424/924 Corporate Network Design and
Implementation
Written by Gene Awyzio September 2002
Review
Requirements Analysis Network Requirements User Requirements Application Requirements Host Requirements
Determining New Customer Requirements
Written by Gene Awyzio September 2002
Overview
Gathering and Listing Requirements Working With Users Service Metrics Characterising Behaviour Developing Performance Metrics Estimating Data Rates Comparing Application Characteristics
Written by Gene Awyzio September 2002
Gathering and Listing Requirements
Determine Initial Conditions These are the basis for the start off
any design project Initial conditions include
Type of project Initial design goals Outside forces
Written by Gene Awyzio September 2002
Gathering and Listing Requirements
Common initial constraints Funding limitations Organizational constraints Existing components
User inertia Customised applications Performance and functional limitations
Knowing initial conditions allows us to make informed design choices
Written by Gene Awyzio September 2002
Working With Users
This allows us to understand user behaviour patterns and environments Applications Usage patterns Requirements
Written by Gene Awyzio September 2002
Service Metrics
Measurable network variables Availability
% uptime or downtime Recoverability
MTBF MTBSO MTTR
Error and loss rates BER CLR CMR Frame and packet loss
Written by Gene Awyzio September 2002
Service Metrics
Capacity metrics Data Rates
Peak Data Rates (PDR) Sustained Data Rate (SDR) Minimum data rate
Data size Burst size Duration
Written by Gene Awyzio September 2002
Service Metrics
Delay metrics End-to-end, round trip, system delay Latency Delay variation (jitter)
Written by Gene Awyzio September 2002
Service Metrics
These metrics are configured and measured using network management platforms SNMP CMIP PING Pathchar
We also need to consider where in the network we want to measure each metric and potential mechanisms
Written by Gene Awyzio September 2002
Characterising Behaviour
Goal: To estimate network performance by gaining understanding of how users and their applications function across the network
Usage patterns Total number of users Frequency of use (sessions/day) Average session length (seconds) Estimated simultaneous sessions
Written by Gene Awyzio September 2002
Characterising Behaviour
Session 1
Session 2
Session 3
Session 4
Application
Sessions
Active Active Active
Active Active Active Active Active Active
Active Active Active
Active Active
Time
Number of Simultaneous sessions
FrequencyDuration
Written by Gene Awyzio September 2002
Characterising Behaviour
Application behaviour considerations Data sizes application will be processing Frequency and time duration of data
passing Traffic flow characteristics
Direction Flow pairs Multicasting
Written by Gene Awyzio September 2002
Developing Performance Metrics
Reliability/availabilityAvailability (% uptime)
AMOUNT OF ALLOWED DOWNTIME
Yearly Monthly Weekly Daily
95% 438h 36.5h 8.4h 1.2h
99.5% 43.8h 3.7h 50.5m 7.2m
99.95% 4.38h 21.9m 5.05m 43.2s
99.98% 1.75h 8.75m 2.0m 17.3s
99.99% 0.88h 4.4m 1.0m 8.7s
Written by Gene Awyzio September 2002
Developing Performance Metrics
Most systems operate at 99.95% 5 minutes downtime per week
Transients (a few seconds) such as rerouting or congestion
One minor interruption per month
Written by Gene Awyzio September 2002
Developing Performance Metrics
Effort and costs to support higher availability can skyrocket Some applications cannot tolerate any
downtime during session Remote control of vehicles
Times of high availability are known and planned for in advance
Many system outages are brief Applications stall for a few seconds These still must be accounted for in overall
availability
Written by Gene Awyzio September 2002
Developing Performance Metrics
Two guidelines for availability measurements Availability is measured end-to-end A loss of availability in any part of the
system is counted in overall availability Availability may be measured
selectively between particular users, hosts or networks
Written by Gene Awyzio September 2002
Developing Performance Metrics
General reference thresholds
99.0 99.5 99.95 99.9899.9
Testbed
Low Performance
High Performance
Written by Gene Awyzio September 2002
Developing Performance Metrics
Thresholds for delay Interaction Delay (INTD)
How long is the user willing to wait for a response Aim for 10 –30 seconds
Human Response Time (HRT) Time boundary when users begin to perceive delay INTD < HRT : Users do not perceive delay Approximately 100ms
Network Propagation Delay Depends on distance and technology
Written by Gene Awyzio September 2002
Developing Performance Metrics
Thresholds for delay
0.01 0.1 1.0 10 100
Delay (Seconds)
Human Response Time
Network Propagation Delay
Interaction Delay
Written by Gene Awyzio September 2002
Estimating Data Rates
Based upon How much you know about the
transmission characteristics of application
Accuracy of estimation Types of estimations
Peak data rate Minimum data rate Sustained data rate
Written by Gene Awyzio September 2002
Estimating Data Rates
Consideration must be given to applications with Large capacity requirements Specific capacity requirements Task completion times (TCT) for
applications May be based upon user expectations or
be set by the application
Written by Gene Awyzio September 2002
Comparing Application Characteristics
If application characteristics can be grouped then we can compare to determine thresholds
High Performance
Low Performance
Written by Gene Awyzio September 2002
Comparing Application Characteristics
The threshold settings may be arbitrary Particularly if applications form a
continuous range of delay