What QOS Solves
As computing and applications become more mission-critical, not to mention more content-rich and multimedia-oriented, the bandwidth necessary to service desktop functionality increases. However, bandwidth availability does not necessarily keep up with the bandwidth appetite of today's desktop applications, creating an environment where there is often more data to be transmitted than there are resources to transmit. The nature of network transmissions only aggravates the problem.
Traditional data transfers are also increasing as a result of the continual addition of new network nodes to existing networks. At the crux of this problem is the fact that there is no inherent means of differentiating between important data, such as data transmitted by mission-critical applications, and excessive data, or data transmitted by interesting (but not necessarily critical) multimedia applications.
Such traditional business applications are continuing to increase in size and in network use, but they are not alone in their hunger for network resources. Multimedia applications can make extensive use of the network, pushing network utilization to its limit (and sometimes beyond). For example, video transmission applications require significant bandwidth to transmit with acceptable levels of quality. Due to the send-as-much-data-as-you-can nature of the most common networking protocol, IP, even a few active instances of these data-intensive programs can create bandwidth strain for networks that were never designed to carry the burden. With data-intensive multimedia applications putting such hefty data loads onto the network, the network often becomes less available for other applications. If the load is significant enough, overall network performance will be affected.
Poor network performance is especially threatening to real-time audio and interactive conferencing transmissions; they are time-sensitive and especially susceptible to delays or individual frame drops delivery. Such delays in the delivery of individual packets can cause problems for real-time audio and real-time conferencing applications.
In the midst of larger traditional applications' higher network utilization, as well as increased network use by emerging desktop applications, core business applications are left vying, sometimes unsuccessfully, for adequate access to the network. These bandwidth-poor and latency-laden characteristics of an overburdened network have an even larger and more dramatic effect on mission-critical applications' use of new multimedia desktop technology: not only do they need access to the burdened network, they need more of the increasingly precious network resources, putting core business applications that use multimedia features in double jeopardy.
If the over-subscription of available network resources is not a bleak enough picture, consider the prevalence of WAN, which introduces an even more critical and more precious bandwidth restriction at the WAN link. With this, the situation is exacerbated.
Mechanisms that manage network activity from an end-to-end perspective are needed to manage over-subscription of network resources, to regulate the allocation of their availability, and to present network data in a means more friendly to a shared network environment. These mechanisms are found in Quality of Service.