Voice over Internet Protocol (VoIP) protocols use data networks to implement voice calling
symptoms of poor VoIP service quality are dropouts, echo, or other glitches in the call
the sequence in which the packets are delivered and variable intervals between packets arriving do not materially affect the application
This type of data transfer is described as bursty
real-time applications can compensate for some amount of packet loss but are very sensitive to delays in data delivery or packets arriving out of sequence
Problems with the timing and sequence of packet delivery are defined as:
Latency
time it takes for a signal to reach the recipient, measured in milliseconds (ms)
increases with distance and can be made worse by processing delays at intermediate systems, such as routers
VoIP can support a maximum one-way latency of about 150 ms
Round trip time (RTT) or two-way latency is the time taken for a host to receive a response to a probe
Jitter
amount of variation in delay over time and is measured by sampling the elapsed time between packets arriving
VoIP can use buffering to tolerate jitter of up to around 30 ms without severe impact on call quality
typically caused by network congestion affecting packet processing on routers and switches
VoIP call quality can only really be established by using a quality of service (QoS) mechanism across the network
QoS means that switches, access points, and routers are all configured to identify VoIP data and prioritize it over bursty data
Enterprise networks can deploy sophisticated QoS and traffic engineering protocols on managed switches and routers
difficult to guarantee QoS over a public network, such as the Internet
On a SOHO network, you may be able to configure a QoS or bandwidth control feature on the router/modem
to prioritize the port used by a VoIP application over any other type of protocol
will help to mitigate issues
should also be able to use the management interface to report connection latency and possibly jitter too
If not, you can use a speed test site to measure latency and bandwidth
If latency is persistently higher than an agreed service level, contact your ISP to resolve the issue