requirement analysis guidelines. 2 process model for requirement analysis gather requirements...
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Requirement Analysis
Guidelines
2
Process Model for Requirement Analysis
Gather Requirements
Develop Service MetricsTo measure performance
Characterizing Behavior
Develop PerformanceThresholds
Distinguishing betweenService Requirements
User/ApplicationPerf. Modifiers
Network Mgmt.Variables
DevelopApplications Map
Initialconditions
ApplicationTypes/groups
Guidelines inDistinguishingservices
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Initial Condition
• Business _______• _______ of design
– New design, modification of an existing design, outsourcing
• _________ of design– Network size, distance, number of sites
• __________– Political, administrative, financial.
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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 ______________.
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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.
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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.
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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.
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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.
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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
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Service Metrics for Delay
• End-to-end, ___________, or system delay
• Latency
• Delay ________
• Timeliness.
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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
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Wide Area Network
LAN LAN
Network Monitorstation
SNMP/CMIP is used to get packet loss data
Ping is used between variousInterfaces to monitor delaysIn the network.
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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
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Results of Characterization Behavior
• Apply a ____________ to the performance requirement for each application.
active
active
active
active active
active active active active
active active
Time
Session 1
Session 2 Session 3
Number of simultaneous sessions
Frequency
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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.
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Step 4: Developing Performance Thresholds
• Criteria for distinguishing between services– A general threshold– An environment-specific threshold – Specific services
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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
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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.
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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 ______ %
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Availability as Measured End-to-End between Networks
Wide Area Network
LAN LAN
Network Monitors
NetworkInterfaces
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Availability as Measured Selectively Between Networks
Server LAN
User LANAvailability
Availability
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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.
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MTBF/MTBSO and Availability for MTTR of 1, 2, and 4 hours
Availability (% uptime)
MT
BF
/MT
BS
O (
Hou
rs)
MTTR4 hours2 hours1 hour
99.099.599.9
8000
4000
2000
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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.
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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.
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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%
99.0 99.5 99.9 99.95
High-performance
Low-performancetestbed
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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.
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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
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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.
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Delay Estimates for User Requirements
Human Response Time
Network Propagation DelayInteraction Delay
0.01 0.1 1.0 10 100
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Distinguishing between Burst and Bulk Applications
• Use ___ and ______ to distinguish between interactive-burst and interactive-bulk applications.
0.01 0.1 1.0 10 100
Interactive-Burst Interactive-Bulk/Burst Interactive-Bulk
Human Response Time Interaction Delay
Delay (Seconds)
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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
Data received/processed
Data received/processed
Delay
Delay
RTTDelay
TCT
Task completed
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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 < __, interactive-bulk; SR >= 3, interactive _______.
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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.
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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).
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Delay Variation
• ______-arrival time of information
• A good rule of thumb is approximately 1% to ___% of the end-to-end delay.
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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.
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Performance Envelop with Generic Thresholds
Low performanceregion
Delay(D)
Reliability (R)
Capacity (C )
High-PerformanceRegions
Generic ReliabilityThreshold
Generic Capacitythreshold
Generic DelayThreshold
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Step 4: Developing Performance Thresholds
• Criteria for distinguishing between services– A general threshold– An environment-specific threshold – Specific services
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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.
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Comparing Application Characteristics
X ms Delay (ms)
App
lica
tion
s
High-performance Low performance
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Sample Plot of a Characteristic as a Continuous Range of Values
X ms Delay (ms)
App
lica
tion
s
High-performance Low performance
Arbitrary Threshold
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Step 4: Developing Performance Thresholds
• Criteria for distinguishing between services– A general threshold– An environment-specific threshold – Specific services
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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
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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
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Fully Developed Performance EnvelopDelay(D)
Reliability (R)
Capacity (C ) Generic ReliabilityThreshold
Generic Capacitythreshold
Generic DelayThreshold
Service Boundary
Serviceguarantees
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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.