Another option is to use a network simulator which is a device that allows you to exactly model the target network and then see the effect of changing key factors such as routing, link speeds and priorities (Voice-over-IP (VoIP) and network performance, 2007). The questions that arise after deployment include: is the VoIP system delivering adequate perceived voice quality? And Is the VoIP application affecting the performance of other applications? Voice is, by definition, analogue in nature and voice quality is highly subjective and the same network may deliver different perceived quality for different voice types. When it comes to measuring voice quality, there are two essential advances- analogue and digital. An analogue voice quality tester works by producing a real voice call across a network and weighing it against the received call with the reference call. A digital voice quality tester works by analyzing the packet data stream containing the VoIP data and measuring packet loss, packet delay and packet jitter. This information is then used to calculate the likely voice quality, expressed as predictive Mean Opinion Score (MOS) (Voice-over-IP (VoIP) and network performance, 2007).

It is important to test for protocol and services interworking, performance, capacity, network strain, and more, because they need to ensure any glitches or shortcomings are identified before the new product or solution is rolled out to the user community, in order to avoid costly and embarrassing problems (Linask, 2009).
References

Linask, Erik. (2009). VoIP Testing Made Easy with Automation. Retrieved May 16, 2010, from TMC News Web site: http://www.tmcnet.com/channels/voip-test-solutions/articles/60010-voip-testing-made-easy-with-automation.htm

VoIP performance testing fundamentals. (2007). Retrieved May 16, 2010, from Search Unified

Communications Web site:

http://searchunifiedcommunications.techtarget.com/generic/0,295582,sid186_gci1260128_mem1,00.html#analyze

Voice-over-IP (VoIP) and network performance. (2007). Retrieved May 16, 2010, from Phoenix

Datacom Web site: http://www.phoenixdatacom.com/voip.htm