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Quality of Service

Quality of Service . CS 457 Presentation Xue Gu Nov 15, 2001. Contents. Definition Taxonomy of real-time applications Integrated services (RSVP) Differentiated services. Definition. Real-time application: sensitive to time.

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Quality of Service

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  1. Quality of Service CS 457 Presentation Xue Gu Nov 15, 2001

  2. Contents • Definition • Taxonomy of real-time applications • Integrated services (RSVP) • Differentiated services

  3. Definition • Real-time application: sensitive to time. • Quality of Service (QoS): providing consistent, predictable data delivery service.

  4. Example • Real Time Audio Example Microphone Speaker AD Converter DA Buffers

  5. Taxonomy of Real-time Applications • Tolerance of loss of data • Tolerant application: audio • Intolerant application: robot control • Adaptability • Delay-adaptive • Rate-adaptive

  6. Approaches to Support QoS • Integrated Services • Fine-grained approach • Provides QoS to individual flow • Differentiate Services • Coarse-grained approach • Provide QoS to large classes of data or aggregated traffic

  7. Integrated Services: Service Classes • Guaranteed service: • Designed for intolerant applications • Packets never arrive after playback time • Controlled load: • Designed for tolerant, adaptive applications • Emulate lightly loaded network

  8. Integrated Services: Overview • Flowspec: the type of service user requires • Admission control: network decides if it can provide the service • Resource reservation: user and network exchange information about the resource • Packet scheduling: how to ensure timely delivery of packets

  9. Integrated Services: FlowSpecs • TSpec: the flow’s traffic characteristics • Bandwidth is not enough because flow rate may fluctuate • Token bucket filter • RSpec: the service requested from the network • Controlled load service: no additional parameters • Guaranteed service: delay target and bounds

  10. Path Resv Resv Failure Integrated Services: Reservation Protocol • Soft state (time out) is used to maintain robustness • Receiver-oriented • Enables flexible increase or decrease of resource allocation • Reservation procedure: R Sender R Receiver R

  11. Integrated Services: Packet Classifying and Scheduling • Classifying packets • Packet header fields are examined • Associated to service classes • Scheduling packets: make sure the packets receive the service • Various queuing methods can be used

  12. Differentiated Services • Traffic is divided into two classes • best-effort service • “premium” • One bit of the header is set to indicate a premium packet • How to deal with premium packets

  13. Differentiated Services: Expedited Forwarding(EF) • Deliver with minimal delay • EF packets arrive no faster than the network can deliver • Edge router is used to control EF arrival rate • Strategy: • Strict Priority: problem is starvation • Weighted Fair Queue

  14. Differentiated Service: Assured Forwarding • Random Early Detection (RED) • Early random drop: packets are dropped probabilistically • Probability P is based on average queue length, thresholds, and current queue packet • If Avglen < MinThresholds queue packets If MinThresholds < Avglen < MaxThresholds compute probability P and drop packets with P If MaxThresholds < Avglen Drop packets

  15. Differentiated Service: Assured Forwarding (Cont’d) • RED with In and Out • Use two separate drop probabilities: “in” is marked for those “premium” packets, “out” for others • When congestion occurs, “out” packets are dropped first • Provide assured service to “in” packets, not guaranteed

  16. Integrated Services Verse Differentiate Services • Integrated Services • Robustness • Worse scalability • Complexity of per-flow control • Differentiated Services • Small increments to current network model • Good scalability • Comparatively easy to implement

  17. Summary • Real-time application • Solution: Quality of Service • Two categories of approaches are reviewed

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