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Quality of Service in VoIP Systems

Updated on September 25, 2013

Poor call quality has historically been a major reason for enterprises holding out on implementing VoIP telephony. While it is less of an issue these days due to improved codecs, hardware and software, businesses still need to analyze and rectify call quality issues on their network. For enterprises that run high volume call centers such as customer support or telemarketing, call quality problems can be unacceptable and unavoidable.

Enterprises often use a combination of hardware and software solutions to test and analyze traffic in a bid to reduce problems which may affect call quality. It enables them to provide a level of assurance for consistent delivery of network traffic and is referred to as Quality of Service (QoS). QoS may be affected by a number of factors such as:

Implementing VoIP QoS
Implementing VoIP QoS


Latency is the time taken for a packet to reach its destination, which can be excessively long if there are delays in the route or the packet takes a longer route to avoid congestion. High latency can cause the talk-over effect seen in poor quality VoIP calls where users start talking because they think the other person has stopped speaking.


Packets from the source can reach the destination in a different order or with delays which can vary unpredictably at the packet level. This is called jitter and system administrators usually try to avoid this by using a jitter buffer which collects packets and puts them in the right order before delivering them to the user.

Packet loss

Sometimes packets can get corrupted because of noise and interference in the route. Other times, packets may not be delivered by the router due to delays or if their buffer is overloaded when it arrives. It is measured as a percentage of lost packets to delivered packets. Packet loss can lead to missing words or even whole sentences during conversations.

Call monitoring may be active (subjective) or passive. Subjective monitoring is usually undertaken by manufacturers or other specialists to test a VoIP network before it is deployed. This enables detection of problems before employees start using it and provides a baseline measurement of normal system behaviour. Passive monitoring analyzes the VoIP traffic in real-time while users make the calls. It allows administrators to identify problems with buffers, latency or unusual congestion etc.

End users may experience echos, delays and missing words in conversations with low quality calls. Such problems, while annoying to consumers, are intolerable for enterprises. Hence it is very important for businesses ensure high QoS through constant quality monitoring and business VoIP redundancy.


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