Analytical description of a parameter-based optimization of the quality of service for VoIP communications

  • Authors:

  • Leopoldo Estrada;Deni Torres;Homero Toral

  • Affiliations:

  • Department of Electrical Engineering, CINVESTAV, IPN, Guadalajara, Jalisco, Mexico;Department of Electrical Engineering, CINVESTAV, IPN, Guadalajara, Jalisco, Mexico;Department of Electrical Engineering, CINVESTAV, IPN, Guadalajara, Jalisco, Mexico and Department of Postgraduate, ITSCH, Las Choapas, Veracruz, Mexico

  • Venue:
  • WSEAS TRANSACTIONS on COMMUNICATIONS
  • Year:
  • 2009

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Abstract

In this work, the perceived quality of VoIP communications is studied. The distributions of the number of consecutive received and lost packets, respectively named gap and burst, of a VoIP communication are modeled with discrete two-state and four-state Markov chains. Algorithms for estimating the transition probabilities between states and from these, the packet loss rate and the respective gap and burst length distributions, are described. Through a study of monitored VoIP calls, it is shown that these models can adequately represent the geometric-type decay of these distributions and that although two-state model performs well for homogeneous losses, for non-homogeneous losses the four-state model fits better. An analysis of the performance of a packet-level FEC scheme, based on N-packet redundancy, is presented. The perceived packet loss rate that results of applying this correction scheme is quantified. For the studied measurements, 1-packet redundancy is sufficient to decrease the perceived loss rate below 1%. Also, the impairments of the perceived quality of voice after the FEC technique and a de-jitter buffer is quantified. The resulting equations can be used to optimize the adjust parameters of the VoIP call, e.g., level of redundancy, type of codec used and de-jitter buffer size. The proposed methodology can be extended if other types of improvements are included.