The setup and completion of a successful VoIP call do not necessarily have the reliability, stability or predictability
of legacy telephony voice services. The performance of traditional telephony can be achieved in Voice over IP (VoIP)/IP telephony deployments only through adequate performance monitoring, measurement and management. What to monitor, measure and manage are now the responsibility of both voice and data technicians.
A caller's phone call setup experience and perception of voice quality are the biggest factors contributing to user satisfaction. While the dialing experience can be objectively measured, however, the caller's judgment of voice quality is subjective.
"A common misunderstanding centers around what constitutes call quality," said Dr. Fiona Lodge at www.prognosis.com. "It's essential that enterprises understand [that] voice quality and call quality are two very different beasts -- each tamed and measured in different ways."
"Enterprises can't afford the risk of providing poor service levels, or a failure to meet compliance standards," she said. "Obviously, voice quality is a big piece of the puzzle, but if you only monitor and manage this small piece, you're missing the bigger picture – and may in fact have a system that provides unacceptable 'experience' levels – even though voice quality is fine." A phone call starts when the user picks up the phone and finishes when the caller disconnects. The calling experience should include all the events and performance that occur during the call. The calling experience is the quality experienced by the user for the entire call, including but not limited to voice quality.
Voice quality alone does not include the other elements -- the delay-to-dial tone, connection success or busy signal, and service availability -- which make up a satisfactory call. Satisfactory evaluation of the calling experience must include what happens when a caller picks up the phone and attempts to connect to the telephone service, all the way through to the disconnect process.
Quality of Experience (QoE) is a newer term that Psytechnics, www.psytechnics.com and Microsoft use that is also related to voice quality and the Mean Opinion Score (MOS). Microsoft has published a paper, "Quality of Experience, A Strategic Competitive Advantage of Microsoft Unified Communications," found here. The use of the term Quality of Experience in this paper is mostly a discussion of the elements of voice quality and the impairments in an IP network. This paper is worth accessing for these impairment discussions.
The caller's experience includes four factors: call quality, voice quality and service quality, which are experienced on every call; and usability of supplementary services, which may also be employed.
- Call quality – Does the caller receive a dial tone within a reasonable period of time -- less than one second? Does the PBX or PSTN complete the call connection? Is the call disconnected properly? Quantifiable parameters should be established, and numerical objectives should be set and then measured for their delivery.
- Voice quality – Can the caller hear the other party? VoIP calls can work in one direction only because of network problems. Is the call loud enough? Can the speaker be recognized? Are the words garbled, distorted or robotic sounding? Is there noise on the call? Parameters for voice quality should be determined, and objectives should be set and then measured for their delivery. Data networks experience latency, jitter and packet loss that cause degraded voice quality. The IP phone's design can compensate for these data network problems. There are, however, significant differences in each vendor's IP phone's ability to fix the data network problems. The IP phones are not all the same in their voice quality performance, especially when the call traverses a WAN. The Mean Opinion Score (MOS) is the numeric value assigned to voice quality. The MOS is used to compare the voice quality performance of different vendors' IP phones.
- Service quality – Is the endpoint, or network, busy? Is the call lost, a condition that occurs with VoIP and is hard to troubleshoot? Was the caller connected to the correct party? Can 800/900 numbers be accessed? Are some phone numbers blocked? There is a very long list of possibilities for service quality.
- Usability of supplementary services – Does the Interactive Voice Response (IVR) application work properly? Does the speech and speaker recognition system work successfully? Does the voice mailbox have adequate storage for the calls? Does the voice mailbox allow a long enough message? One major enterprise allows only a 15-second voice message.
Voice quality is important. The other three factors -- call quality, service quality and the usability of supplementary services -- should also be considered when determining the user's satisfaction when placing a voice call.
About the author:
Gary Audin has more than 40 years of computer, communications and security experience. He has planned, designed, specified, implemented and operated data, LAN and telephone networks. These have included local area, national and international networks as well as VoIP and IP convergent networks in the U.S., Canada, Europe, Australia and Asia.
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