Requirement Analysis Guidelines

2 Process Model for Requirement Analysis Gather Requirements Develop Service Metrics To measure performance Characterizing Behavior Develop Performance Thresholds Distinguishing between Service Requirements User/Application Perf. Modifiers Network Mgmt. Variables Develop Applications Map Initial conditions Application Types/groups Guidelines in Distinguishing services

3 Initial Condition Business _______ _______ of design –New design, modification of an existing design, outsourcing _________ of design –Network size, distance, number of sites __________ –Political, administrative, financial.

4 Importance of Initial Condition Knowing the type and scope of the network project will help you to________your design efforts. These conditions apply when you are doing the _________ of a design. Stand a much better chance of understanding and working with these ______________.

5 Step 1. Requirements collection Develop a ______ or questionnaire for users. Arrange a meeting or whiteboard session to discuss their _____________. Spend time with one or more high- performance _______ to get immersed in their environment.

6 Results of Requirement Collection A listing of __________ –A concise, easy-to-use list –Help you to identify what’s _________ for your environment. –Determine __________s between various requirements. Mapping Applications –Application _________ information used to show their relative locations in the design environment.

7 Step 2: Developing service metrics to measure performance Service metrics are either actual ________ variables in the network, or are derived from measured variables. Performance requirement is useful only if it is _________, __________, and _______ within the network. Service metrics will depend on your design environment and the types of equipment you implement in the network.

8 Service metrics for reliability Availability –In terms of _______ uptime and downtime. Recoverability or stability –In terms of mean time between failure (______), mean time between service outage (_________), and mean time to repair (________) Error and loss rates at various levels –Bit error rate (_____), ___________ (CLR), cell misinsertion ratio (CMR), and frame and packet loss rates.

9 Service Metrics for Capacity Data _______s –In terms of peak data rate (PDR), sustained data rate (SDR), and minimum data rate. Data ______ –Including burst size and duration

10 Service Metrics for Delay End-to-end, ___________, or system delay Latency Delay ________ Timeliness.

11 Results of Service Metrics Configurable and measurable quantities in network _____________ systems, such as SNMP, CMIP,.. Other available tools –Ping –Pathchar –Tracert Service metric where metric will be measurement measured in system method

12 Wide Area Network LAN Network Monitor station SNMP/CMIP is used to get packet loss data Ping is used between various Interfaces to monitor delays In the network.

13 Step 3: Characterizing Behavior Usage ________s – number of sessions/user-day –Average time/session –Average number of active user sessions Application __________ –Data size to be processed –Frequency and time duration for data to be passed across the network –__________ characteristics (direction) –Degree of multicasting Models –Merge to one session –Statistical formulas for modeling

14 Results of Characterization Behavior Apply a ____________ to the performance requirement for each application. active Time Session 1 Session 2 Session 3 Number of simultaneous sessions Frequency

15 Step 4: Developing Performance Thresholds _______ for distinguishing between services –A_________ threshold for separating performance requirements into low-performance and high- performance. –An _____________________ threshold for separating requirements into low-performance and high- performance. –_______ services will have known bounds or guarantees.

16 Step 4: Developing Performance Thresholds Criteria for distinguishing between services –A general threshold –An environment-specific threshold –Specific services

17 Reliability Requirements Availability –How much downtime can be expected per _____________ Availability Amount of allowed downtime (hours [h], minutes[m] (% uptime) seconds [s] per time period) Yearly monthly weekly Daily 95% 438 h 36.5 h 8.4 h 1.2 h

18 How can availability be measured? _________ should availability be measured ? What service ________ can be used to measure it?  How we measure availability indicates what we consider to be _________ in the system.

19 Guidelines for Availability Measurement Availability is measured __________ between –Users, hosts, or networks, or –Particular users, hosts, or networks. A loss of availability in ____ part of the system is counted against any overall availability metrics. General threshold is ______ %

20 Availability as Measured End-to- End between Networks Wide Area Network LAN Network Monitors Network Interfaces

21 Availability as Measured Selectively Between Networks Server LAN User LAN Availability

22 Recoverability Using MTBF/MTBSO and MTTR. –_______: estimation of how long system outages may last; related to repair time in a service contract. –MTBF/MTBSO: estimation of the __________ of system outages. –  together states how long and frequency outages may be, but availability estimate does not have that level of detail. More specific in how ______ system outages last and how ______ they occur. Example: 99.98% can be 15 minutes outage/day or 1.5 h outage/year General threshold: MTTR of 1 hour and MTBF/MTBSO of 4000 hours.

23 MTBF/MTBSO and Availability for MTTR of 1, 2, and 4 hours Availability (% uptime) MTBF/MTBSO (Hours) MTTR 4 hours 2 hours 1 hour

24 Error and Loss Rates More complex than availability and recoverability More commonly used the __________ level. –Per _____ or circuit, such as BER –Between network equipment, such as CLR, CMR (cell misinsertion ratio, between ATM equipments) or packet loss rates (between network layer routers). –End-to-end, between hosts or applications. May be measured at the ____ and network layers, and reported as percentage of available traffic in the network.

25 Threshold for Reliability Good methods to estimate availability thresholds for your environment. –Evaluate the availability requirements of each of the __________s that will be used in your environment, from discussions with users of the applications or from documentation for each application. –Determine low-performance/high performance thresholds –Estimate availability based on the probable _________ paths that the applications will use, and what equipment and services exist or may be in those paths.

26 Availability Threshold Summary Testbed or prototype reliability (availability): –less than ___ Low-performance reliability: –less than ______% High-performance reliability: –greater than or equal to 99.9% High-performance Low-performance testbed

27 Recoverability Threshold Low-performance reliability: –MTTR greater than __ hours or an MTBF/MTBSO less than 8000 hours High-performance reliability: –MTTR less than or equal to __ hours and MTBF/MTBSO greater than to equal to 8000 hours.

28 Error rates Low-performance –IP packet losses of >25% for < 2 hours/month 10% < packet loss < 25% for 2 hours/month 1% < packet loss < 10% for < 5 hours/month < 1 % for the remainder of the month

29 Delay Requirements Threshold for Delay –_________ delay (INTD) How long a user is willing to wait for a response from the system during an interactive session. (10 to 30 seconds) Important for interactive applications. –Human _________ time (HRT) The time boundary when users begin to perceive delay in the system. (100ms) Important for highly interactive applications. –Network _________ delay Lower bound to the end-to-end and round-trip network and system delays.

30 Delay Estimates for User Requirements Human Response Time Network Propagation Delay Interaction Delay

31 Distinguishing between Burst and Bulk Applications Use ___ and ______ to distinguish between interactive- burst and interactive-bulk applications Interactive-Burst Interactive-Bulk/Burst Interactive-Bulk Human Response Time Interaction Delay Delay (Seconds)

32 Task Completion Time (TCT) Another approach for distinguishment The amount of time work is being performed by the system before __________ with the user is required. Source Destination Data received/processed Delay RTT Delay TCT Task completed

33 System Responsiveness System responsiveness = ________, when HRT/RTT > or =1 and System Responsiveness = HRT/__________, when HRT/RTT < ____ –HRT/RTT describes the degree of responsiveness inherent in the _______. –Small RTT, system responsiveness would be within the ______ time –Large RTT, delay would impact system responsiveness SR = 3, interactive _______.

34 Results of Delay Analysis Whether there are delay requirements for ___ of the applications, or whether all applications can use a ________ service. If there are delay requirement, how strict they are, in terms of: –___________ –_________ levels (boundaries, thresholds, and guarantees)  distinguishing between applications that have real-time, interactive-burst, interactive bulk, and asynchronous delays.

35 End-to-End Delay End-to-end delay is useful in measuring and monitoring delay in an environment. It is based on combinations of –___________ of the network –Host and _______ element hardware and software performance, including network protocols –Application behavior at particular delay thresholds –User ________ with the system at particular delay threshold. Key guideline: determine the limiting factor between these delay thresholds (_________ within the system).

36 Delay Variation ______-arrival time of information A good rule of thumb is approximately 1% to ___% of the end-to-end delay.

37 Capacity Requirements Estimating data rate –Estimate ______ data rate (PDR), minimum data rate, sustained data rate (SDR), or a combination of these. –Estimate a data size and ______s. –Different applications can be estimated differently based on how much information you know about the ______________ characteristics (and data flow) of the application. _____ general thresholds between low- and high- performance capacity –It has a secondary impact on performance, through reliability and delay.

38 Performance Envelop with Generic Thresholds Low performance region Delay(D) Reliability (R) Capacity (C ) High-Performance Regions Generic Reliability Threshold Generic Capacity threshold Generic Delay Threshold

39 Step 4: Developing Performance Thresholds Criteria for distinguishing between services –A general threshold –An environment-specific threshold –Specific services

40 Environment-specific Service Thresholds The ____________ indicates what the performance thresholds should be. Distinguish low- and high-performance characteristics for each environment (environment-specific thresholds), and not __________ characteristics across environment.

41 Comparing Application Characteristics X ms Delay (ms) Applications High-performance Low performance

42 Sample Plot of a Characteristic as a Continuous Range of Values X ms Delay (ms) Applications High-performance Low performance Arbitrary Threshold

43 Step 4: Developing Performance Thresholds Criteria for distinguishing between services –A general threshold –An environment-specific threshold –Specific services

44 Specified Services Deterministic Services –More _________ performance characteristics than the best-effort services. –Use _________ to approximate where the high and/or low-performance levels are. –No guarantee is given

45 Guaranteed Services Need to have ___________ performance characteristics. There is some mechanism to ________ the service to the application or user. ________ is often useful to protect traffic flows downstream from a flow that exceeds its service limit and attempts to use more network resources than are contracted. Time Guarantee Application behavior Policing No action taken

46 Fully Developed Performance Envelop Delay(D) Reliability (R) Capacity (C ) Generic Reliability Threshold Generic Capacity threshold Generic Delay Threshold Service Boundary Service guarantees

47 Distinguishing Between Service Performance Levels Guideline –Determine if any of the _________ have obvious requirements for specified performance from the system. –______ application, such as mission-critical, real-time, or controlled rate. –Apply application ______ to the applications. –Otherwise, most likely best effort.