Thursday, September 17, 2009
04:30 PM in MATH 175
Professor Bowei Xi
Department of Statistics, Purdue University

VoIP: Analysis and Modeling

Abstract

Network engineering for quality-of-service (QoS) of Internet voice communication (VoIP) can benefit substantially from simulation study of VoIP packet traffic queueing, which requires accurate statistical models for packet arrivals. This article describes statistical analyses that result in validated models. Work began with a 48-hr collection of VoIP arrival times and headers of 1.315 billion packets from 332,018 calls on a link of the Global Crossing network. Modeling is based on comprehensive analysis of the marginal distributions and time dependencies of call-level properties (arrivals, durations, bit-rates, and transmission and silence intervals), and packet-level properties (timestamp accuracy, jitter, and 20-ms packet-counts). Two models result that generate packet-level traffic in one direction of a link. A semi-empirical model first generates a Poisson call-arrival process which provides the times of the first packets of the calls; the packet interarrival times for each call are those of a random sample from an empirical database of 277540 semi-calls (packets in one direction of a call). Validation of the representativeness of the semi-calls is complex. A parametric model replaces the semi-call sampling by generation of modeled call durations, generation of modeled transmission and silence intervals, and inserting 20-ms packet arrivals within transmission intervals.

Refreshments will be served at 4:00 PM in HAAS 111.