Mitel MiVoice Business Voice Quality And Troubleshooting Manual page 12

Voice Quality Troubleshooting Guide
TERM
On Premise Station (ONS)
Packet Delay
Packet Loss
Ping Test
Public Switched Telephone Network
(PSTN)
Quality of Service (QoS) in the analog
and TDM network
Quality of Service (QoS) in the IP
network
Reflection
6
Table 1: Voice Quality Terminology
Stations which are installed on the same premises as the PBX, or
which can operate satisfactorily with the system when installed in
adjacent premises without special circuit arrangements.
The amount of time required for a packet to traverse the network.
Packet delay can be measured by a ping test.
The loss of data fragments (packets) during transmission over an IP
network. In a VoIP network, a packet is considered lost if it never
arrives at its destination or if it arrives too late to be used. When
packet loss occurs during a VoIP call, tiny fragments of the
conversation are lost. This issue can result in choppy voice quality.
A utility that you can use to determine the round-trip packet delay
between a PC and a MiVoice IP Phone on the network.
The world-wide, public, circuit-switched telephone network. It consists
of telephone lines, fiber optic cables, microwave transmission links,
cellular networks, communications satellites, and undersea telephone
cables, all inter-connected by switching centers, allowing any
telephone in the world to communicate with any other.
The performance of a communications channel or system is usually
expressed in terms of QoS. The QoS will relate to the type of system,
SNR (Signal to Noise Ratio), BER (Bit Error Ratio), maximum and
mean throughput rate, reliability, priority, and other factors specific to
each service.
Quality of service is the audio quality experienced by an IP phone user
while on a call. It is not the network equipment settings. However,
certain network equipment configurations can help ensure that users
receive adequate QoS. These configurations include:
- IEEE 802.1p/Q (802.1Q VLAN now included as part of 802.1d): This
is also known as VLAN tagging, priority, or COS (different from the
PBX/telecom Class of Service). IEEE 802.1p/Q operates at Layer 2
to ensure the highest priority for voice traffic.
- DiffServ (also known as DSCP): DiffServ is a fixed field in the Layer
3 information that is also used to define different service categories
through TOS, priority, and precedence. DiffServ and Type of
Service are similar. The older Type-of-Service values are
compatible with the newer DiffServ values.
In this document, reflection is when a portion of a signal is sent back
towards the signal's source. If the round-trip delay in the reflections is
short (less than 50 ms), the reflections are perceived by users as
sidetone. However, if the round trip delay is long (greater than 50 ms)
the reflections are heard as echo. Reflection can be caused by line
hybrids or by acoustic or mechanical audio coupling at the phone.
DEFINITION
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