2001/09/26 Chin-Kai Wu, CS, NTHU 1

Resource Allocation and Resource Allocation and Management in DiffServ Management in DiffServ Networks for IP TelephonyNetworks for IP Telephony

Maarten Büchli, Danny De Vleeschauwer, Jan Janssen,

Annelies Van Moffaert, Guido H. Petit

11th International workshop on Network and Operating Systems support for digital audio and video, June 25 - 26, 2001, Port Jefferson, NY USA

2001/09/26 Chin-Kai Wu, CS, NTHU 2

OutlineOutline Introduction

Voice Traffic Model Quality of Service

End-To-End Delay Analysis Mouth-to-ear delay Queuing delay

Simulation

Results

2001/09/26 Chin-Kai Wu, CS, NTHU 3

IntroductionIntroduction In DiffServ, a scheduler is needed in order to

guarantee throughput and delay to the different aggregate flows in the system.

The class-based Weighted Fail Queuing (WFQ) is considered. Hence, dimensioning the bandwidth for the voice traffic is therefore of great concern.

The paper shows how to set the weights of a WFQ scheduler in a DiffServ router such that a certain delay bound is met.

2001/09/26 Chin-Kai Wu, CS, NTHU 4

Voice Traffic ModelVoice Traffic Model

Steps

Packet Size

Analog Voice

Sample Quantize Encode Packitize

M: voice packet sizeRcod: codec bit rateTpack: packetization delaySOH: header overhead

2001/09/26 Chin-Kai Wu, CS, NTHU 5

CBR voice flows is well modeled by a Poisson process, and cannot become more bursty than it.

Voice sources that use VAD (Voice Activity Detection) are much harder to characterize.

2001/09/26 Chin-Kai Wu, CS, NTHU 6

Quality of ServiceQuality of Service

2001/09/26 Chin-Kai Wu, CS, NTHU 7

Capacity assigned to voice traffic

Queue load

Cvoice: capacity of voice trafficφvoice: weight of voice traffici: number of queues

ρ: queue loadBvoice: average bit rate of voice flows

2001/09/26 Chin-Kai Wu, CS, NTHU 8

Mouth-to-ear delayMouth-to-ear delay

Deterministic part Tpack, packetization Tser, serialization Tprop, propagation Tdejitter, dejittering Toth, other (encoding, decoding etc.)

Stochastic part Tqueue, queuing delay

2001/09/26 Chin-Kai Wu, CS, NTHU 9

Only interested in the maximum queuing delay. For this delay, a reasonable quantile can be used since this is the fraction of packets that arrive in time.

The queuing delay has to be compensated for in the dejittering buffer of the receiver. Hence, the dejittering delay should be chosen equal to a quantile of the queuing delay.

When perfect dejittering is used, the queuing and dejittering delay of each packet is equal to the maximum queuing delay.

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Delay distribution

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Queuing delayQueuing delay

R: reserved rateb: max burst sizeM: max voice packet sizeN: number of hopsMTUi: MTU at node iCi

link: link capacity at node i

Ri: reserved rate at node ibi: max burst size at node i

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Simulation ScenarioSimulation Scenario

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Simulation ResultsSimulation Results

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ResultsResults

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