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Metrics for Network Services

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

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Metrics for Network Services

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  1. Metrics for Network Services CIT 443

  2. Service Metrics • Timeliness • Capacity • Quality

  3. Service Metrics • Measurable • Valid • Accurate • Timely

  4. 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

  5. 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

  6. 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

  7. Timeliness – Causes of Latency • Physics • The speed of the light is the speed of light… • Signaling • Switching Delay • Queue Depths

  8. 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

  9. Capacity • Bandwidth vs Throughput • Ideally, throughput = capacity • Highly dependent on underlying technologies in use • 2nd order equation

  10. 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

  11. 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

  12. 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)

  13. Capacity • Scalability • Network Growth • Long Term vs Short Term • “Bottleneck Management” • 80/20 rule

  14. Quality • Accuracy • Efficiency • Availability • Reliability

  15. 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

  16. 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

  17. 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%

  18. 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

  19. 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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