B - 4 MC75 User Guide

Voice Packet Prioritization
IP soft phones transmit voice packets in the same manner as any other appli cation that sends data over the
network. On a network with different types of traffic, voice packets are given the same priority as any other tr affic,
and therefore may be subject to delays.
WiFi Multi-media (WMM) is a solution to this problem. WMM is a specification that supports prioritizing traffic, and
“higher-priority” packets can be given preferential treatment.
To make use of WMM, the devices that generate traffic must mark their packets as high or normal pr iority in a field
in the IP packet called Differentiated Services Code-Point (DSCP). The wireless inf rastructure, which must be
configured to support WMM, gives a higher priority to packets that have been marked a s high priority through
DSCP marking by the devices that generate traffic.
VQM detects if there is an ongoing Voice over WiFi (VoWiFi) call, and if so, marks outgoing vo ice packets (Only
outgoing voice packets can be marked. The incoming voice packets have al ready been through the network, so it
makes no sense to mark them.) as high-priority using DSCP. This enables WMM-compatible wireless infrastructure
to treat the voice packets preferentially. This results in fewer delays for voice packets, which in turn improves the
call quality.

Acoustic Echo Cancellation

Acoustic Echo occurs during a voice call when the audio from the earpiec e enters the microphone of the same
device. This results in the person at the other end hearing back a delayed versi on of his/her own voice (“Echo”).
Needless to say, “Echo” is not desirable, and needs to be suppressed. This is the functio nality performed by the
Acoustic Echo Canceller (AEC). There are two approaches to suppres sing the Echo:
•
Turn the Acoustic Echo Canceller (AEC) on permanently. This approach is not very efficient because the
device consumes more power when the AEC is on.
•
Turn the Acoustic Echo Canceller (AEC) on only when there is an ongoing call.
VQM follows the second of the two approaches mentioned above.
VQM automatically turns on the Acoustic Echo Canceller (AEC) w hen the mobile device is in a VoWiFi call. When
the call is terminated, VQM turns the AEC off. Note that the AEC is turned on for spea kerphone and handset
modes and does not get turned on for wired headset and Bluetooth headset modes. The AEC is not required for
wired headset because the audio volume is quite low (because of the proximi ty of the earpiece to the ear), and
therefore it is very unlikely for the audio from the earpiece to go in to the mouthpiece . Bluetooth headsets typically
have an Echo Canceller built in. Turning the AEC on only while on a call saves batter y power, compared to leaving
the AEC turned on permanently.
The AEC is not turned on for Cellular calls because the WWAN phone application has a built-in echo canceller.

Limitations

•
There is no VPN support in VQM.
•
Only the Avaya softphone is supported.
Disabling VQM
To disable VQM perform a warm boot.