Quality of Service with VoIP

By Stan Baldwin
Updated: February 01, 2011

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.

QoS Management

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:

  1. They “watch” the internet traffic flowing through their device for volume (bandwidth) and type. They record and report on parameters, including the ones most important to VoIP; lost data, latency and jitter. Traffic should be “watched” across many devices, depending on the complexity of the network, so Quality of Service software is not located on only one device (except in very simple systems). At the very least, your ISP has a QoS package they use to assure they are delivering the level of service they promised your organization (and they can also use to suggest additional services when you begin to come up against the current capacity limitations).
  2. The information gathered is available to your IT folks to configure the appropriate devices (such as routers, gateways, ATAs and bridges) to prioritize types of traffic and allocate bandwidth. Typically voice and video traffic are given highest priority. Voice and video are also frequently allocated a minimum level of bandwidth to further assure service quality. Optimizing the flow of network traffic for VoIP can deliver the best QoS to your users and deliver the best return on your bandwidth investment.

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.

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