Avaya Enterprise Voice Audio Quality User Manual
Nortel Communication Server 1000 and Business Communications Manager
Enterprise Voice Audio Quality
Troubleshooting
Enterprise Voice – Audio Quality Troubleshooting
Revision History
April 2006
Standard 3.00. This document is up-issued to support Nortel Communication Server
1000 and Business Communications Manager. Updated document numbering.
March 2006
Standard 2.00. This document is up-issued to support Nortel Communication Server
1000 and Business Communications Manager. Updated formatting and platform
support information.
February 2006
Standard 1.00. This document is issued to support Nortel Communication Server
1000 and Business Communications Manager.
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Enterprise Voice – Audio Quality Troubleshooting
Contents
Abstract ..................................................................................................................................... 4
Audio Quality Impairments......................................................................................................... 4
Defining the Problem ................................................................................................................. 5
Call Example 1 - IP set to IP set ............................................................................................ 6
Call Example 2 - IP set to PSTN residential line .................................................................... 6
Impairments............................................................................................................................... 7
Head Set ................................................................................................................................ 7
Telephone .............................................................................................................................. 8
Side Tone............................................................................................................................... 8
IP Network ............................................................................................................................. 9
Virtual/IP Trunk ...................................................................................................................... 9
Gateway Configuration...........................................................................................................9
Call Server ............................................................................................................................10
Loss and Level Plan..............................................................................................................10
Clocking ................................................................................................................................11
Recorded Announcement / Message on Hold.......................................................................11
Analog Trunks.......................................................................................................................11
Digital Trunks ........................................................................................................................12
Public Switched Telephone Network.....................................................................................12
Residential Lines ...............................................................................................................12
Business to Business Calls ...................................................................................................13
How to make Test Calls............................................................................................................14
How to perform captures over a longer period of time..............................................................14
Appendix A – Echo Tutorial ......................................................................................................16
Appendix B – IP Audio Tools....................................................................................................20
Appendix C – TDM Audio Capture Tools..................................................................................21
Appendix D – Audio Problem Tracking Sheet...........................................................................22
Glossary ...................................................................................................................................23
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Enterprise Voice – Audio Quality Troubleshooting
Abstract
Although audio quality is subjective, tools and methods are discussed in this document
that you can use to objectively investigate and resolve audio quality issues. This
document provides an overview of common problems encountered when using
Enterprise Voice, provides tools and techniques to resolve audio quality issues, and
introduces common troubleshooting terminology used. In addition to reading this
document, Nortel recommends that you consult the Engineering Guidelines for the
phone, headset, and other connected audio devices.
Audio Quality Impairments
In this document, an impairment is defined as any reduction of the quality of the audio in
a call. Audio quality can be impaired by problems with Enterprise Voice equipment, or by
problems on the public switched telephone network (PSTN). The following are the most
common impairments, applying to both Time Division Multiplexed (TDM)
communications, and to Packet Based Audio communications (VoIP or VoFR for
example).
Low/High audio levels – a low signal level can impact audio quality, and a low
signal-to-noise ratio can cause the noise in the call path to impair audio. A high
signal level can lead to distortion.
Distortion - any modification of the original audio, such as high audio level
clipping, phase shifts, and frequency shifts.
Noise – background acoustic noise, or noise electrically induced in the call path.
Echo – an audible reflection of the speaker’s voice, delayed in time.
Delay – the length of time it takes for the talker’s audio to reach the listener.
Clock slip – differences in clocking references can cause clicks and pops due to
audio deletion.
Cross Talk – audio from a different call can be heard.
No audio or one-way speech path – neither party can hear or be heard, or only
one party can hear the other.
The following impairments only apply to Packet Based Audio communications:
Packet Loss – loss of audio information due to data network issues.
Jitter – variation in the delivery rate of packets across the network.
Compression – the use of audio compression techniques to reduce bandwidth
requirements. This includes Transcoding as well as Multiple Encodings.
Further sections in the document describe where these impairments can occur.
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Enterprise Voice – Audio Quality Troubleshooting
Defining the Problem
Defining the problem to be solved is usually the most difficult aspect of audio
troubleshooting, due to the subjective and often intermittent nature of audio problems. A
good approach is to interview a sampling of users, and use the resulting data to look for
common characteristics that can help you define what conditions lead to audio
problems.
Interview the users who reported a problem, and other users who did not report any
problem. Use the following guidelines when interviewing users:
Ask open ended questions such as “Describe what you heard”. Do not ask “Did
you hear echo?”
Try to get details on the call path – who was called and how was the call
established. For example, a call between an ACD agent and a residential home
phone is a call path, but the real call path was PSTN caller dialed IVR system
which transferred to a Branch Office via Virtual Trunk to an IP Phone.
Look at the equipment on the user’s desk. Note the phone type in use. Note the
accessories in use (headset, amplifier, recording device etc.).
Look for any patterns in the trouble reports. For example: Are problems more
prevalent on inbound calls versus outbound? Are problems reported on calls
between two phones on the local system? Is the time of day a factor?
Make note of the background noise in the environment.
Does the user use handsfree, handset or headset?
If echo is described, try to determine when and for how long echo occurred in the
call. Was echo heard only at the beginning of the call, throughout the call, or
intermittently during the call?
If brute force data collection must be used, try the following techniques:
Configure the telephone with a special key or key press feature that creates a
debug log with a date/time stamp of a problem call. On CSE1000 systems, you
can use Malicious Call Trace or an Activity key. On BCM, you can use Feature
9*9 to provide a MTT Stamp in the system logs.
Provide a select group of end users a data collection sheet that contains the
following columns:
Date/Time, Internal/External Call, Headset/Handset/Handsfree, Problem,
Constant/Intermittent. If possible, provide check boxes to make it easier for users
to provide feedback.
Have the users email the completed form to their Help Desk
Review the data you collected by interviewing users and analyze the call path. Look for
a pattern that helps you understand the problem.
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Enterprise Voice – Audio Quality Troubleshooting
Node Based Troubleshooting
In this document, a node is defined as is any device that can affect the audio
characteristics of a call. By looking at the audio path as a sequence of clearly defined
nodes you can verify that each node is correctly configured, and apply appropriate
troubleshooting techniques.
Following are two examples of a call path and the nodes in the path.
Call Example 1 - IP Phone to IP Phone
Problem reported – Caller A finds the audio from Caller B loud and distorted. Caller A
does not experience this with other callers. Caller B does not report any problems.
Node 1 – Caller A headset
Model – GN-Netcom – on adapter (not batteries)
Node 2 – Caller A IP Phone
Model – Nortel i2004/P2 running D98 software
Node 3 – IP Network
Model – obtain a diagram of the network
Node 4 – Caller B IP Phone
Model – Nortel i2004/P2 running D98 software
Node 5 – Caller B headset
Model – GN-Netcom – on adapter (not batteries)
Call Example 2 - IP Phone to PSTN residential line
Problem reported – Caller A (ACD agent) receives an inbound queue call from a home
residence and hears a low level echo throughout the call.
Node 1 – Caller A headset
Model – GN-Netcom – on adapter (not batteries)
Node 2 – Caller A IP Phone
Model – Nortel i2004/P2 running D98 software
Node 3 – IP Network
Model – obtain a diagram of the network
Node 4 – Voice Gateway Card (VGW)
Model – 32 port SMC running 4.00.55 software
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Enterprise Voice – Audio Quality Troubleshooting
Node 5 – PRI card
Model – Dual Port PRI card
Node 6 – PRI Span
Model – Acme ILEC local PRI
Node 7 – Residential Phone Line
Model – Acme ILEC local loop
Node 8 – Residential Phone
Model – Cordless
Now that the call path has been broken down into manageable pieces, we will now look
at a number of common impairments at different nodes in the call path, and how to
resolve them.
Impairments
This section discusses the factors that can have an impact on audio quality.
Headset
Headsets provide flexibility and comfort for users. However, because each user can
have a different brand and model of headset, it is difficult to predict the audio quality
experienced by each user. Wireless headsets add additional issues because they are
sometimes prone to delay and information loss. To minimize headset problems, take the
following steps:
Use the mid range on the side tone (if adjustable on the amplifier) and TX/RX
levels whenever possible to stay in the linear operation of the amplifier(s). Once
the telephone and headset audio levels are optimized, use the headset receive
volume level slider on the headset amplifier (if applicable) for minor adjustments
during calls.
Headset microphone placement can also have a large impact on audio quality
and overall noise levels. Follow the manufacturer recommendations. A general
rule is 1 inch away from the corner of the mouth (just out of the breath stream
from the nose and mouth).
Verify the power source – batteries or AC wall adapter. If noise or hum is
present, try batteries instead of the AC power.
When troubleshooting echo or noise problems, use the MUTE button on the
headset amplifier to help isolate the source of the echo/noise. For instance,
muting the amplifier removes the headset as the noise source. Muting at the
phone itself removes the amplifier and headset as possible sources.
The Nortel Wireless i22xx handsets have a configurable Noise Mode which can
improve the signal-to-noise ratio of the transmitted audio by reducing the
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Enterprise Voice – Audio Quality Troubleshooting
microphone sensitivity. However, when the user leaves the noisy environment for
a quiet environment, the transmitted audio can be too low in volume.
PC based IP Telephony such as the MCS5100 Client or the i2050 utilize a Nortel
tested and approved USB Audio Headset. This headset is recommended to
ensure that the audio quality is the best possible since it does not rely on the PC
Audio Card.
Telephone
All telephones are not manufactured to meet the same standards, and therefore audio
characteristics vary from one telephone to another. The use of handsfree and cordless
telephones add even more possibilities for impairments.
Check the receive volume level settings on the telephone and set it to mid range
whenever possible. (Use the same method for handsfree operation). Using the
mid range volume reduces the chance of acoustic coupling between the speaker
and microphone.
If handsfree is in use, observe the background noise levels and placement of the
phone in relation to the user – is a good signal-to-noise ratio possible? In other
words, can people hear the speaker over background noise?
Most TDM handsfree telephones use an echo suppressor – loss is inserted to
control acoustic echo generated at the handsfree telephone. Newer TDM and IPbased telephones use a Digital Signal Processor (DSP) to cancel the acoustic
echo that is created. DSP-based cancellation is often smoother and less intrusive
in the conversation flow than echo suppression.
A worn or faulty handset curly cord can introduce echo via EMI.
Cordless phones often use audio companding/compression to reduce the radio
bandwidth required, automatic gain control, and noise cancellation techniques.
These cordless phone characteristics can cause echo issues to occur because
the echo tail path appears to be changing. To determine if this is a problem, test
the connection using a wired 2500 telephone and see if the problem is resolved.
Side Tone
Side tone is the name given to the small amount of audio from your telephone speaker
that is picked up by the telephone microphone. The purpose of side tone is to provide
feedback that the phone is operating, and to mask any echo. Due to the development of
telephony standards, the frequency characteristics and loudness of the side tone is
different than on older TDM telephones. This change can cause users to report a
problem. If side tone concerns are reported:
Capture the bidirectional audio using Ethereal or a TDM recorder. Compare the
captured audio with the user’s experience. If the issue is side tone, the problem
will NOT be heard in the Ethereal or TDM recordings.
Record the handset audio via a device such as the “THAT-1” from
www.jkaudio.com
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