Avaya Definity SI Maintenance Manual page 161

Multimedia Call Handling (MMCH)
For some Avaya Vistium endpoints, if an external speaker is attached or was
attached when the system was last rebooted, this endpoint will cause audio echo
throughout the conference. First, isolate the offending endpoint by asking each
endpoint to mute, one at a time, until the echo disappears.
If the input from an endpoint is located too close to the speakers of an endpoint,
then acoustic echo is created. The microphone must be moved away from the
speakers.
Normally, if any microphone in the room is moved relative to the speakers, that
site will cause echo until the echo canceller in the codec retrains itself, some will
require a manual reset. If a PictureTel keypad is configured with external
microphones connected to the keypad, then the internal microphone and external
microphone(s) "sing" to each other if the "ext mic" bat switch is set to "int mic" on
the back of the keypad. In this configuration, VAS locked on that site, and the
acoustic "singing" was inaudible.
Rate Adaptation
Because of a lack of a clear explanation in standards, sometimes endpoints do
not work well with each other and the DEFINITY MMCH. The MMCH will only
allow a conference to downgrade from 64kbps to 56 kbps operation on
conferences that have the Rate Adaptation flag set to y .
When a downgrade does occur, information on the Status Conference form
indicates the success or failure of the 64kbps-endpoints that are participants to
properly rate adapt to 56kbps. As a general indication that the conference has
rate adapted, the Conference Transfer Rate and Effective Transfer
Rate fields show initial and current transfer rates, respectively. For each 64-kbps
endpoint the column that indicates Rate Adapt shows an n if the endpoint did
not follow the procedures as specified by the H.221. If an endpoint shows y , it did
successfully rate adapt. If an endpoint shows c , it joined the conference at
56kbps.
Once the conference rate adapts, the endpoints that do not properly follow suit,
will become audio-only endpoints. A conference will not rate adapt from 56 kbps
back to 64 kbps until all endpoints disconnect from the conference and it idles.
The PictureTel 1000 Release 1.1C, PictureTel 6.01 software, and the Vistium 2.0
software successfully rate adapt with the MCU. External rate adaptation
techniques used by VTEL and CLI are known to cause problems with the endpoint
when used with this feature.
Endpoint or I-MUX in Loopback Mode
Some endpoints have a loopback enable feature. This makes DEFINITY MMCH
data loopback at the MMCH when a connection is in progress. The loopback can
be enabled prior to or during a connection.
555-233-123 Issue 4 May 2002 5-57