When talking with someone on a traditional telephone system, the quality of the connection never enters your mind, unless static intrudes or a connection is dropped. With traditional PSTN, degradation in connection quality is rare these days. Over the decades steady improvement in the land-line system has produced an expectation for flawless conversations, anywhere in the world.
Voice over Internet Protocol (VoIP) has a much shorter history but benefits from the vast amount of technical and financial investment driving the rapid evolution of the internet. Assuring the Quality of Service for a voice (or video) connection over the internet, because each connection is “built” from a potentially enormous number of devices and connecting cables, appears to be a much more difficult goal. While a block diagram describing the connections and flow of data traffic for even a small organization can be intimidating, in a business setting VoIP services have little difficulty matching the call performance we've come to expect from the PSTN. If you are the decision maker for your organization's planned VoIP system there are a couple basics to keep in mind to assure your users never coming looking for you with malice in their eyes.
All (or essentially all) of the vocal sounds made by one party need to arrive “instantly”, in the correct order, and appropriately spaced, at the ear of the other party. The “pipe” between them cannot restrict the flow of information. Having a large enough “pipe” to assure every bit of data poured across it meets zero resistance due to other traffic (congestion) is generally a good idea. This philosophy has been termed “over-provisioning” and approaches bandwidth specifications from the perspective “If some is good, more's better, and too much is just enough.” For a simple network, over-provisioning may be effective and relatively inexpensive, but when the block diagram of devices and connections begins to look like the map of the Tokyo Metro, more serious consideration is called for.
As with all things internet, the number of Quality of Service (QoS) products is impressive. From freeware to complex proprietary hardware/software devices, the choices all provide some combination of the following services:
As an organization grows, the QoS system will alert the IT staff to increase bandwidth where it is needed. With a well-implemented QoS system and a large enough “pipe”, the users will enjoy the same instant, clear connections world-wide with the VoIP system, as they have with the PSTN.