Adaptive Codec Selection for VoIP in Multi-Rate WLANs

Adaptive Codec Selection for VoIP in Multi-Rate WLANs

Anna Sfairopoulou (Network Technologies and Strategies (NeTS) Research Group, Universitat Pompeu Fabra, Spain), Carlos Macián (Network Technologies and Strategies (NeTS) Research Group, Universitat Pompeu Fabra, Spain) and Boris Bellalta (Network Technologies and Strategies (NeTS) Research Group, Universitat Pompeu Fabra, Spain)
DOI: 10.4018/978-1-59904-820-8.ch005
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Abstract

Network Technologies and Strategies (NeTS) Research Group, Universitat Pompeu Fabra, SpainThis chapter introduces the problems caused to voice over IP calls on 802.11 networks due to the link adaptation mechanism of them. It provides an overview of all the components participating in this study with special emphasis on the multi-rate anomaly. Furthermore, it reviews the literature on recent works on the specific area of link adaptation and codec selection. The authors finally propose as a solution to the multi-rate problem a codec selection mechanism, which, by changing codec of some of the calls at the moment of the rate change, has as an objective to maintain delay and packet loss values in acceptable levels and provide the desired QoS for the voice flows.
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Voip Over Wlans

Voice over IP (VoIP) over wireless LANs (WLANs) has been a hot research topic during the past years due to the widespread deployment and ease-of-use of both technologies. The capacity of a wireless cell in terms of number of supported calls, as well as the quality of the voice transmission over the wireless link under different channel conditions, are crucial for deciding whether this technology can be widely deployed and accepted for voice service. In spite of all the research efforts in this area, there are still unsolved issues concerning the quality of VoIP calls, most commonly caused by the specific wireless network characteristics listed below (note that the purely physical effects, such as meteorological impact on channel conditions, are beyond the scope of this chapter):

  • 1.

    Unfairness between uplink and downlink streams

  • 2.

    High protocol layer overheads

  • 3.

    Fast VoIP degradation in presence of TCP flows

  • 4.

    Variable capacity due to multi-rate transmissions

Although the first three problems have been widely analyzed in previous works, there is scarce bibliography considering the last problem. Multi-rate transmission is one of the key features of the IEEE 802.11 PHY/MAC specifications, which allows each mobile node to select its physical layer parameters (modulation and channel coding) to optimize the bit transmission over the noise/fading-prone channel. These sporadic rate changes occurring on the mobile nodes as they move around the cell due to the link adaptation algorithm of the 802.11 specification have an impact on the transmissions of all active calls and produce a general degradation of the network performance.

This chapter intends to provide an overview of the impairments observed on voice flows due to the multi-rate characteristic of 802.11, and discuss some of the solutions that have been proposed so far, with particular focus on a codec adaptation solution. Main goals are:

  • 1.

    To give some background on VoIP over WLAN systems and analyze the source of the various problems and how they affect the voice transmission in terms of total cell capacity and quality of service

  • 2.

    To describe what is a multi-rate wireless LAN and its impact on VoIP calls

  • 3.

    To review the literature on how to best cope with the multi-rate problem and introduce the benefits of a codec adaptation solution

  • 4.

    To present a cross-layer codec adaptation algorithm and demonstrate how it is able to satisfy the QoS needs of VoIP traffic

  • 5.

    To examine the suitability of proposing some future enhancements to the SIP architecture to better cope with this issue

Complete Chapter List

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Table of Contents
Foreword
Abbas Jamalipour
Preface
Nicola Cranley , Liam Murphy
Chapter 1
Ronan Skehill, William Kent, Dorel Picovici, Michael Barry, Sean McGrath
This chapter introduces quality of service in multi-access wireless networks. Specifically it demonstrates how QoS is implemented in IEEE 802.11 and... Sample PDF
Evaluating QoS in a Multi-Access Wireless Network
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Chapter 2
Dirk Staehle, Andreas Mäder
This chapter gives an overview of the background and functionality of the high speed downlink packet access (HSDPA), and provides insights into the... Sample PDF
Radio Resource Management Strategies for HSDPA-Enhanced UMTS Networks
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Chapter 3
Nidal Nasser, Tarek Bejaoui
Major research challenges in the next generation of wireless networks include the provisioning of worldwide seamless mobility across heterogeneous... Sample PDF
Handoff Management in Next Generation Wireless Networks
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Chapter 4
Ming Li, Roberto Riggio, Francesco De Pellegrini, Imrich Chlamtac
This chapter provides a comprehensive review of the architectures, algorithms, and protocols in the topic of resource management in IEEE... Sample PDF
Resource Management in IEEE 802.11 Based Wireless Networks
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Chapter 5
Anna Sfairopoulou, Carlos Macián, Boris Bellalta
Network Technologies and Strategies (NeTS) Research Group, Universitat Pompeu Fabra, SpainThis chapter introduces the problems caused to voice over... Sample PDF
Adaptive Codec Selection for VoIP in Multi-Rate WLANs
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Chapter 6
Michael M. Markou, Christos G. Panayiotou
This chapter introduces the network buffer control techniques as a mean to provide QoS. This problem has been extensively studied in the context of... Sample PDF
Buffer Control Techniques for QoS Provisioning in Wireless Networks
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Chapter 7
Gabriel-Miro Muntean, Janet Adams
Wireless networks are becoming a part of everyday life for many people. When a mobile device has wireless LAN capability, multimedia content can be... Sample PDF
Power Saving in Wireless Multimedia Streaming to Mobile Devices
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Chapter 8
Jose Luis Jodra, Fidel Liberal, Begoña Blanco Jauregi
This chapter introduces the principal characteristics of MANETs and shows how these particularities may affect both QoS conditions and QoS... Sample PDF
Multimedia Services Provision in MANETs
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Chapter 9
Andrej Kos, Mojca Volk, Janez Bester
Commonly understood as the next generation networks (NGN), a composite environment of proven telecommunications and Internet-oriented mechanisms has... Sample PDF
Quality Assurance in the IMS-Based NGN Environment
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Chapter 10
Marcio Nieblas Zapater, Graça Bressan
This chapter discusses the quality assurance of multimedia services over IP networks from the end user standpoint and introduces the concept of... Sample PDF
Quality of Experience for Video Services
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Chapter 11
Dorel Picovici, John Nelson
Perceptual voice quality measurement can be defined as an objective quantification of an overall impression of the perceived stimulus. An... Sample PDF
Perceptual Voice Quality Measurements for Wireless Networks
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Chapter 12
Tacha Serif, Gheorghita Ghinea
This chapter describes an investigation exploring user experiences of accessing streamed multimedia content, when that content is tailored according... Sample PDF
Enhancing the Multimedia Tour Guide Experience: Transmission Tailoring Based on Content, Location, and Device Type
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Chapter 13
Harilaos Koumaras, Fidel Liberal, Lingfen Sun
The concept of PQoS, although in general it deals with the user satisfaction with a specific delivered/ requested service, is in practice... Sample PDF
PQoS Assessment Methods for Multimedia Services
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Chapter 14
Peifang Zhang, Scott Jordan
Emerging wideband code division multiple access (WCDMA) data services will likely require resource allocation to ensure that throughput targets are... Sample PDF
Scheduling and Access Control for Wireless Connections with Throughput Guarantees
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Chapter 15
Paolo Chini, Giovanni Giambene, Snezana Hadzic
Nowadays there is an increasing need of broadband communication anytime, anywhere for users that expect to receive multimedia services with support... Sample PDF
Broadband Satellite Multimedia Networks
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Chapter 16
Panagiotis Papadimitriou, Vassilis Tsaoussidis
An increasing demand for multimedia data delivery coupled with reliance in best-effort networks, such as the Internet, has spurred interest on... Sample PDF
End-to-End Support for Multimedia QoS in the Internet
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Chapter 17
Tarek Bejaoui, Nidal Nasser
This chapter introduces the cross layer design for resource allocation over multimedia wireless networks. Conventional layered packet scheduling and... Sample PDF
Cross-Layer Radio Resource Management Protocols for QoS Provisioning in Multimedia Wireless Networks
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Chapter 18
Gürkan Gür, Suzan Bayhan, Fatih Alagöz
This chapter introduces the QoS issues and support in transport protocols for wireless multimedia transmission. After an overview of the transport... Sample PDF
Transport Protocols and QoS for Wireless Multimedia
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