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Metrics for Network Services. CIT 443. Service Metrics. Timeliness Capacity Quality. Service Metrics. Measurable Valid Accurate Timely. Why use metrics?.

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Service metrics l.jpg
Service Metrics

  • Timeliness

  • Capacity

  • Quality


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Service Metrics

  • Measurable

  • Valid

  • Accurate

  • Timely


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Why use metrics?

Metrics are key indicators that can be used to identify and understand the behaviors, successes, and failures of specific functions, processes, or systems


Timeliness l.jpg
Timeliness

  • Response Time

    • Amount of time between a request for service and the receipt of the subsequent reply

    • Users vs Computers

      • Users are impatient

      • Interactivity

      • Computers can be extremely patient


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Timeliness

  • Latency/delay

    • Time between data being ready to send and the actual transmission of that data

    • Occurs at multiple points in a network

      • Why?

    • Often expressed as the total latency for a path between two nodes

    • Latency is a fact of life


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Timeliness – Causes of Latency

  • Physics

    • The speed of the light is the speed of light…

  • Signaling

  • Switching Delay

  • Queue Depths


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Timeliness- Delay Variations

  • Amount of variation in delay

    • Jitter

  • Has a large negative effect on streaming technologies/protocols

    • If it is predictable, then it can potentially be buffered

  • A good target: 2% (or less)

  • Frame sizing


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Capacity

  • Bandwidth vs Throughput

  • Ideally, throughput = capacity

    • Highly dependent on underlying technologies in use

    • 2nd order equation


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Capacity

  • Utilization

    • % of total availability in use at any given time

    • Optimal Utilization

      • Maximum average utilization before the network is considered saturated.

      • Depend on underlying technology

        • Ethernet vs Token Ring


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Capacity

  • Offered Load

    • Sum of the data the network has available to send at any given time

  • Data Rates

    • Peak Data Rate

    • Sustained Data Rate

    • Minimum Data Rate


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Capacity - Estimating Data Rates

  • Distributed Computing

    • 103 seconds (with data size 105 MB)

  • Web Transactions

    • 10 seconds (with data size 102 MB)

  • Database Transactions

    • 10 seconds (with data size 102 MB)

  • Teleconferencing (multicasting)

    • 1 second (with data size .5 MB)


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Capacity

  • Scalability

    • Network Growth

    • Long Term vs Short Term

    • “Bottleneck Management”

    • 80/20 rule


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Quality

  • Accuracy

  • Efficiency

  • Availability

  • Reliability


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Accuracy

  • The percentage of traffic that is error free

  • Accuracy for WAN links is usually described as being under or over the threshold bit error rate (BER)

    • Analog lines BER=1 in 105

    • Digital lines (copper) BER=1 in 106

      • Vs 109 – 1010 for LAN

    • Digital lines (fiber) BER=1 in 1011

  • Accuracy for LAN links is typically described in terms of frames error rate


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Efficiency

  • Amount of useful data transmitted compared to total number of bits transferred

  • Inverse percentage of overhead

    • Smaller headers=more efficiency

    • Larger frames/packets/cells=more efficiency

      • Assuming error free transmission

  • Dependent upon technology


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Availability

  • What percentage of time is the network up and available to meet the business needs of customers compared to the total time the network is designed to be operational

  • Expressed as a percentage

    • Or number of nines

  • Cost of downtime

    • Mission critical systems cannot be down without significant loss of revenue opportunity costs

  • No mention of when the network is available

    • Most networks have critical times that the system much be functional

  • High performance

    • Availability >= 99.9%


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Reliability

  • How often the network fails and how long it takes to repair it

  • MTBF

    • Mean Time Between Failures

    • High performance MTBF >=8000 hours

  • MTTR

    • Mean Time To Repair

    • High performance MTTR <= 2 hours

  • Both of these parameters have individual component/link bases and end-to-end bases

    • End-to-end is the product of the individual bases

    • .999 * .999 * .999 = .997


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Types of Service

  • Best effort

    • As much bandwidth as we can get

  • Deterministic Services

    • Estimate of required bandwidth, but no means of guaranteeing bandwidth

  • Guaranteed Services

    • A means of enforcing bandwidth is implemented

    • As bandwidth approaches upper boundaries policing takes place to limit bandwidth consumption


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