Why is quality of service (QoS) so challenging in Voice over IP (VoIP) implementations? Are there different steps that can be taken to ensure there won't be voice distortion and other issues?
The main reason for this challenge is that most forms of VoIP service, especially for residential subscribers, are provided over the public Internet. This is a primary reason why VoIP is cheaper than legacy telephony, which also happens to be the primary reason people make the switch. Everything comes with a price, and in this case, the trade-off is quality and reliability. When traversing the public Internet, VoIP is provided on a "best efforts" basis, meaning that it performs very well when there is sufficient bandwidth, but that can be highly variable.
QoS refers to a metric that reflects the performance of VoIP based on a variety of factors that apply to voice traffic running over an IP network. Maintaining a high level of VoIP quality of service is one of the best ways to demonstrate that VoIP can perform at a carrier-grade level. When VoIP runs over a private IP network, QoS is high, mainly because the carrier has end-to-end control over the connection and can prioritize voice over other forms of data traffic.
Most VoIP traffic, however, runs over the public Internet, where operators do not have that ability. This means that VoIP must share bandwidth with everything else. And even though it only consumes a nominal amount of broadband, its performance is highly sensitive to even nominal variances caused by bandwidth-intensive applications such as streaming video or online gaming. VoIP providers, therefore, are at the mercy of how their subscribers are using the full gamut of online applications, and invariably there will be poor quality VoIP sessions when overall network activity peaks.
For more information about VoIP quality of service, read our tip on VoIP traffic management and prioritization.
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