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VoIP: Quality is King

Most businesses are adopting IP telephony, or Voice over IP (VoIP), for several very good reasons: significant cost savings, increased productivity from more integrated communications, and the ability to leverage wireless LANs for greater worker mobility. Convergence of all enterprise data, video and voice applications onto a common IP infrastructure minimizes overall capital and operational expenditures, reduces monthly fees paid to incumbent wireline and mobile carriers, enables new productivity-enhancing applications and business processes, and affords many additional business benefits.

But after investing in IP Quality of Service (QoS) provisions to prepare the enterprise network for convergence and VoIP traffic, some businesses experienced a severe degradation in call quality. Why is that? Why do some companies seem to get lucky with their VoIP implementations, while others have a bad experience? Why is voice quality perceived as great or awful? And, can anything be done to avoid or solve this problem?

This article will answer these important questions by explaining the issues involved and outlining some steps any business can take to enjoy the many benefits of VoIP while avoiding the problems caused by poor voice quality.

The Relationship between Voice Quality and Productivity

“Can you hear me now?” This question, asked routinely by mobile phone users, is all too common with VoIP communications, as well. Poor voice quality is more than an inconvenience, which in the case of mobile phones is at least balanced by a major convenience–mobility. But with enterprise VoIP, the difficulties communicating constantly undermine productivity, which threatens to erase the financial gains achieved through network convergence and IP telephony.

Consider customer call centers as an example. By automating call centers through interactive voice response systems, the enterprise saves money on staffing while maintaining customer satisfaction through self-service options that reduce wait times. While a staffed call may cost a company about $10, an automated call may cost only about $1. Moreover, in this application, voice quality makes the difference between delivering satisfactory service levels and causing frustration for the customer, who is forced to press “0” to speak with an operator, resulting in a lost customer who hangs up instead.

The incumbent carriers in the Public Switched Telephone Network (PSTN) long ago recognized the importance of good voice quality, and have conducted substantial research to understand the many issues involved. The result is an infrastructure that delivers consistently high levels of voice quality.

It is this “pin drop” call quality provided by the PSTN that now sets the standard by which organizations should measure their own IP telephony implementations. Indeed, it is entirely reasonable for the workforce to expect the same level of call quality and network reliability from their IP-based telephone service.

The Relationship between IP QoS and Voice Quality

Businesses have been told by network equipment vendors that they will enjoy sufficient VoIP call quality in a converged network by implementing a few IP QoS provisions. This claim is only partially true.

The need for QoS provisions derives from the fact that neither Ethernet nor IP was designed originally to carry real-time traffic, such as VoIP communications. Numerous extensions needed to be made to both Ethernet and the basic Internet Protocol suite to initiate and terminate calls (e.g. the Session Initiation Protocol), to handle real-time traffic streams (e.g. the Real-Time Protocol), to minimize latency and jitter by prioritizing VoIP calls (e.g. Class of Service for Ethernet and Differentiated Services for IP), and to improve traffic management (e.g. the Resource Reservation Protocol and Call Admission Control).

While all of these provisions do make it possible to operate a converged enterprise network with better overall performance, not one addresses any challenges that are unique to voice communications. The problem is familiar to anyone who has participated in a call that utilizes VoIP at one or both ends. There can be a hollow sound on the line or noise in the background. Speech is often garbled and, at times, unintelligible. Annoying echoes and clipping sounds can make it impossible to carry on a conversation. One participant may need to shout just to be heard by the other. At this point, the participants on the call may wonder if it was worth switching to IP at all.

The incumbent PSTN carriers understand these issues, known as impairments to voice communications, and have tuned and enhanced their network infrastructures to minimize or eliminate the adverse effects on voice quality. In fact, the technique for measuring voice quality depends entirely on just how successful the carrier has been at minimizing or eliminating these impairments (see sidebar on Measuring Voice Quality).

About Karl Brown: Brown brings more than 15 years of experience in network communications to his position at Ditech Networks, spanning the wireline, wireless, voice, and data industries, and has worked for both equipment vendors and service providers. Prior to joining Ditech as Director of Product Marketing and Product Management, Brown held marketing positions at ANDA Networks, Jetstream Communications, and Nortel Networks.

As Vice President of Marketing, Brown is responsible for Ditech’s market strategy, product management, product marketing, and corporate marketing programs, and focuses on the development of new markets for the company’s core technologies.

Also by Karl Brown: Measuring Voice Quality.

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