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Quality of Service Introduction

Quality of Service Introduction. Special Topics in Communications Networks: QOS Hanoch Levy Computer Science Tel-Aviv University 2000. What is QoS?. User wants its data (service) to arrive: “Completely” “On time” What is “completely”?

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Quality of Service Introduction

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  1. Quality of Service Introduction Special Topics in Communications Networks: QOS Hanoch Levy Computer Science Tel-Aviv University 2000 .Levy, Advanced Comm, CS, TAU, DOS

  2. What is QoS? • User wants its data (service) to arrive: • “Completely” • “On time” • What is “completely”? • What is “on time”? ==> a) Function of service b) Function of money .Levy, Advanced Comm, CS, TAU, DOS

  3. Example: Web transfer chain • User computer ISP (proxy) network server User computer servers .Levy, Advanced Comm, CS, TAU, DOS

  4. test: Why QoS?1.Limited Resource • QoS is an issue due to limited resource problem. • If resources are unlimited ==> no “quality” problem. • Got to consider in light of some predictions of bandwidth becomes ”unlimited”. .Levy, Advanced Comm, CS, TAU, DOS

  5. Why QoS2. Variety of Services • Problem of QoS simplifies under single objectives == single service. • e.g. -- telephone system -- quality problem was not an issue. • e.g. -- butttt. Cellular phone -- quality is an issue. .Levy, Advanced Comm, CS, TAU, DOS

  6. Why QoS(cont) • Problem of QoS magnifies in light of multiple objectives == multiple services. • Two quality dimensions: • Time constraints (timely service) • Precision • Two traffic characteristics • Quantity (rate) • Burstiness .Levy, Advanced Comm, CS, TAU, DOS

  7. Services • Voice: Timely - high Precision - low Volume - medium Burstiness - medium • Email: Timely - low precision - high volume - variable (low - huge)burstiness - might be high .Levy, Advanced Comm, CS, TAU, DOS

  8. Services (cont) • Web: Timely - medium precision - high volume - medium burstiness - high • IRC: Timely - medium-high precision - high volume - small burstiness - small .Levy, Advanced Comm, CS, TAU, DOS

  9. Services (cont) • Live Video: Timely - high precision - low volume - highburstiness - highFTP: Timely - low precision - high volume - highburstiness - depends .Levy, Advanced Comm, CS, TAU, DOS

  10. Effects of Variety • Makes mechanisms complex • Can benefit from sophistication ==> can get good utilization! .Levy, Advanced Comm, CS, TAU, DOS

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