Zebra MC55A0 User's Guide download pdf (Page 169)

Technical Specifications C - 3

If the MC75A and the Bluetooth headset are un-paired, there is no way to go back to the Bluetooth headset

using the VQM icon. The only way to reconnect the Bluetooth headset to the device is by using the BTExplorer

application.

If the user taps the VQM icon when a wired headset is connected to the MC75A, the audio mode does not

change.

The audio continues to get routed to the wired headset.

If the user taps the VQM icon while not on a call there is not change to the audio mode.

To view the VQM versions numbers tap > File Manager. Navigate to the Windows folder and search for

VQMAudioNotify.exe file.

A dialog box displays listing the versions numbers.

Figure C-2

VQM Audio Control Dialog Box

Voice Packet Prioritization

IP soft phones transmit voice packets in the same manner as any other application that sends data over the

network. On a network with different types of traffic, voice packets are given the same priority as any other

traffic, 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 priority in a

field in the IP packet called Differentiated Services Code-Point (DSCP). The wireless infrastructure, which

must be configured to support WMM, gives a higher priority to packets that have been marked as 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 voice packets (Only

outgoing voice packets can be marked. The incoming voice packets have already 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 earpiece enters the microphone of the same

device. This results in the person at the other end hearing back a delayed version of his/her own voice

(“Echo”). Needless to say, “Echo” is not desirable, and needs to be suppressed. This is the functionality

performed by the Acoustic Echo Canceller (AEC). There are two approaches to suppressing 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) when 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 speakerphone and

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Zebra MC55A0 User's Guide Page 169