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. Quality of Service (QoS): providing consistent, predictable data delivery service.

Example Real Time Audio Example AD Converter DA Buffers Microphone Speaker

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

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

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

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

Integrated Services: FlowSpecs TSpec: the flows 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

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: Sender R R R Receiver Path Resv Failure Resv

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

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

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

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

Differentiated Service: Assured Forwarding (Contd) 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

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

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