VoIP Service Problems
How Serious Are VoIP Service Problems
By Mae Kowalke,
In recent years, IP telephony services and applications have changed the way
voice, video, and data are delivered over computer networks.
But, useful as converged delivery of voice, video, and data over computer networks is, IP telephony
doesn’t always work as well as it should. Packet deliveries can get misdirected or hung up, causing problems with voice or video quality, for
example, or delays in data delivery.
That’s where Quality of Service, or QoS comes in—a system for directing network traffic in the most
efficient and appropriate way possible.
Causes
TMCnet recently asked Cliff Liles, Senior Product Manager at Kentrox, to explain the most common IP
quality problems, and how Quality of Service resolves them.
On networks that deliver mixed traffic types (VoIP and Video, for example), Liles said that there are two main contributors to the sorts of
problems QoS can address.
1. Congestion on the circuit.
Congestion can occur momentarily or for extended periods of time. When there is congestion, indiscriminate packet discards can
occur, causing holes in the data stream.
The more holes, the greater the degradation, Liles said. “Data (TCP) will retransmit and correct for lost packets. For this reason, congestion
will typically slow data delivery but not interrupt it.”
Quality of Service solves the problem of congestion on the circuit by identifying important data applications and ensuring that they get higher
priority than less important applications.
2. Variable Packet Length
Voice packets are usually short, and data packets are usually long. Problems occur when time-sensitive packets get stalled in
buffers behind long data packets. When that happens, jitter can be introduced into the voice stream.
“A VoIP packet that arrives too late (later than the length of the receiving device's streaming buffer) will cause a hole in the traffic just as
if had been lost,” Liles explained.
Stalled packets also can cause problems with interactive video. Quality of Service prioritization prevents time-sensitive packets from
getting stalled.
VoIP Service Problem Symptoms
So how do you know if congestion on the circuit, or stalled packets, is causing problems on your network?
Liles defined a few symptoms (and their causes) that indicate you need a Quality of Service solution.
Echo
Echo in the voice stream is a symptom of long Latency
(delayed delivery). “In voice transmission, Latency can cause echo unless echo cancellers are employed, and will create the ‘talk over’ affect
where one person tries to talk before the other has finished,” Liles told TMCnet.
Dropped calls
Dropped calls are a sign of a severe problem
with jitter (variability in delay). Jitter is a Latency (delay) issue. Jitter also can cause noisy or scratchy voice quality, and serious
problems with video, Liles added.
Slow data delivery
If data is
arriving slowly, that’s a sure sign you need a QoS solution, which can “prioritize important (mission critical) traffic over general data traffic
to avoid performance problems where it matters,” Liles said.
Article from http://www.tmcnet.com/
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