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 Time Number of Simultaneous sessions Frequency Duration

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/availability Availability (% uptime) AMOUNT OF ALLOWED DOWNTIME YearlyMonthlyWeeklyDaily 95%438h36.5h8.4h1.2h 99.5%43.8h3.7h50.5m7.2m 99.95%4.38h21.9m5.05m43.2s 99.98%1.75h8.75m2.0m17.3s 99.99%0.88h4.4m1.0m8.7s

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 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 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