E-Model MOS Estimate Precision Improvement and Modelling of Jitter Effects

Adrian Kovac,Michal Halas

doi:10.15598/aeee.v10i4.739

Abstract

This paper deals with the ITU-T E-model, which is used for non-intrusive MOS VoIP call quality estimation on IP networks. The pros of E-model are computational simplicity and usability on real-time traffic. The cons, as shown in our previous work, are the inability of E-model to reflect effects of network jitter present on real traffic flows and jitter-buffer behavior on end user devices. These effects are visible mostly on traffic over WAN, internet and radio networks and cause the E-model MOS call quality estimate to be noticeably too optimistic. In this paper, we propose a modification to E-model using previously proposed Pplef (effective packet loss) using jitter and jitter-buffer model based on Pareto/D/1/K system. We subsequently perform optimization of newly added parameters reflecting jitter effects into E-model by using PESQ intrusive measurement method as a reference for selected audio codecs. Function fitting and parameter optimization is performed under varying delay, packet loss, jitter and different jitter-buffer sizes for both, correlated and uncorrelated long-tailed network traffic.

Highlights

IntroductionThe Internet, VoIP and in general IP traffic are known to possess the property of being self-similar, long-range dependent (LRD) or in other words “bursty”
The Internet, VoIP and in general IP traffic are known to possess the property of being self-similar, long-range dependent (LRD) or in other words “bursty”.The behavior of a “bursty” traffic differs from ideal stochastic model of independent packets when trying to evaluate traffic interarrival times via wellknown distributions
Statistical tests showed as a proof of concept, that Generalized Pareto distribution (GPD) Pareto distribution is the most suitable one for describing interarrival times of general long-tailed LAN/WAN packet streams impaired by random jitter with equal distribution

Summary

Introduction

The Internet, VoIP and in general IP traffic are known to possess the property of being self-similar, long-range dependent (LRD) or in other words “bursty”. The behavior of a “bursty” traffic differs from ideal stochastic model of independent packets when trying to evaluate traffic interarrival times via wellknown distributions This property translates into the failure of general queuing models, such as M/M/1/k, which counts on Exponential and Poisson characteristics of input stream and service time, to describe the situation of incoming VoIP stream at buffer on the receiver’s side. “MOS modified E-Model” – shows estimate performed via software using E-Model [4] incorporating the effects of jitter and buffer size based on actual codec configuration and data about network performance from RTCP without physically observing or interfering with packet stream behind jitter buffer. The actual discrepancy of EModel estimate, being around 1.00 MOS scale under 40 ms jitter is unacceptable for all purposes These network conditions are not unreal and are common on WiFi and mobile connections

Brief E-model Description

Network Delay Description and Statistics

Proposed E-Model Modification to Impairment Factor

Test of Results

Conclusion