Design Requirements

1. Design Requirements IACT424/924 Corporate Network Design and Implementation

2. Review • Requirements Analysis • Network Requirements • User Requirements • Application Requirements • Host Requirements • Determining New Customer Requirements Written by Gene Awyzio September 2002

3. 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

4. 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

5. 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

6. Working With Users • This allows us to understand user behaviour patterns and environments • Applications • Usage patterns • Requirements Written by Gene Awyzio September 2002

7. 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

8. 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

9. Service Metrics • Delay metrics • End-to-end, round trip, system delay • Latency • Delay variation (jitter) Written by Gene Awyzio September 2002

10. 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

11. 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

12. Characterising Behaviour Number of Simultaneous sessions Frequency Duration Session 1 Session 2 Session 3 Session 4 Active Active Active Application Sessions Active Active Active Active Active Active Active Active Active Active Active Written by Gene Awyzio September 2002 Time

13. 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

14. Developing Performance Metrics • Reliability/availability Written by Gene Awyzio September 2002

15. 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

16. 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

17. 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

18. Developing Performance Metrics • General reference thresholds High Performance Low Performance Testbed 99.0 99.5 99.9 99.95 99.98 Written by Gene Awyzio September 2002

19. 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

20. Developing Performance Metrics • Thresholds for delay Human Response Time Interaction Delay Network Propagation Delay 0.01 0.1 1.0 10 100 Delay (Seconds) Written by Gene Awyzio September 2002

21. 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

22. 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

23. High Performance Low Performance Comparing Application Characteristics • If application characteristics can be grouped then we can compare to determine thresholds Written by Gene Awyzio September 2002

24. Comparing Application Characteristics • The threshold settings may be arbitrary • Particularly if applications form a continuous range of delay Written by Gene Awyzio September 2002