Yealink SIP-T48G Administrator's Manual page 261

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Check if the IP phone is configured to obtain the time and date from the NTP server
automatically. If your phone is unable to access the NTP server, configure the time and
date manually.
If you have poor sound quality/acoustics like intermittent voice, low volume, echo or
other noises, the possible reasons could be:
Users are seated too far out of recommended microphone range and sound faint,

or are seated too close to sensitive microphones and cause echo.
Intermittent voice is mainly caused by packet loss, due to network congestion, and

jitter, due to message recombination of transmission or receiving equipment (e.g.,
timeout handling, retransmission mechanism, buffer under run).
Noisy equipment, such as a computer or a fan, may cause voice interference. Turn

off any noisy equipment.
Line issues can also cause this problem; disconnect the old line and redial the call

to ensure another line may provide better connection.
The IP phone only uses logo file in DOB format, as the DOB format file has a high
compression ratio (the size of the uncompressed file compared to that of the
compressed file) and can be stored in smaller space. Tools for converting BMP format to
DOB format are available. For more information, refer to
File on page 99.
Press the volume key to increase or decrease the ringer volume when the IP phone is
idle, or to adjust the volume of engaged audio device (handset, speakerphone or
headset) when there is an active call in progress.
Troubleshooting
Customizing a Logo Template
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