Mitel MiVoice Business Voice Quality And Troubleshooting Manual page 21

In Scenario 2:
1. With respect to reflection and echo, the PSTN treats the MiVoice Business LS trunk like a
2-wire analog phone. The hybrid on the Mitel LS trunk card generates a reflection into the
PSTN network just like the reflection created at the hybrid in the 2-wire PSTN phone.
2. The ONS line on the MiVoice Business platform does not introduce any significant delay
that could cause echo. Therefore, you are not responsible for cancelling reflections from
entering the PSTN for the benefit of the CPE 2-wire analog phone on the other side of the
PSTN.
3. There are six hybrids, two for each 2- wire segment, each of which contributes reflections
towards the Mitel 2-wire analog phone. The delays through the network are normally so
short that these reflections are heard as sidetone and the MiVoice Business platform does
not need remove these reflections.
4. These six hybrids also each generate a reflection in the direction of the 2-wire analog phone
on the other side of the PSTN. Again, the delay of these reflections is typically short enough
that these reflections are all heard as sidetone.
5. If the PSTN introduces a delay that is long enough for the reflections to result in echo, then
the PSTN is responsible for placing echo cancellers in the audio path. In this case, the
PSTN will normally insert a pair of echo cancellers, one at each end. These echo cancellers
prevent both the 2-wire PSTN analog phone and the 2-wire Mitel analog phone from hearing
echo.
6. There are three hybrids in the Mitel CPE that cause reflections in the direction of the PSTN
2-wire analog phone. Since the delay though the MiVoice Business system is short, these
three reflections cannot be distinguished from a single reflection and can be handled by
the PSTN as if they originated from a single two-wire phone hybrid.
7. The 2-wire analog phone may generate acoustic, mechanical, or crosstalk reflections.
Normally the levels of these reflections are much lower than the hybrid reflection, with
approximately the same delay, so no acoustic echo canceller or suppressor is needed.
However, if the 2-wire set has a handsfree mode, echo suppression will be needed because
of the louder levels and the additional delays caused by longer acoustic echo paths.
8. If Mitel equipment inserts long delays that cause echo, you are responsible for cancelling
the reflections that cause the echo. Delayed reflections that cause echo may occasionally
be caused by handsfree acoustic echo or long PSTN delays.
Scenario 3
In scenario 3, a MiVoice IP Phone is connected via IP to the MiVoice Business platform; the
MiVoice Business platform is connected to the PSTN via PRI trunk; the PSTN is connected to
a VoIP Gateway via LS trunk; and a VoIP phone is connected via IP to the gateway.
Analog, TDM, or PSTN Network Issues
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