Nortel 2001 Installation And Operation Manual page 217

Nortel IP Softphone 2050 Page 217 of 430
Softphone 2050. The IP Softphone 2050 contacts the chosen TPS, and if the
IP Softphone 2050 is valid, registers it with the system. The registration
information is then saved to the IP Softphone 2050.
Loss plan
The USB Headset Adapter provides the IP Softphone 2050 with a fixed loss
plan compliant with the TIA-810A specification. If other headsets or audio
devices are used, the loss plan is unknown and undefined. Nortel supports the
resolution of audio problems only for the USB Headset Adapter.
Echo cancellation
Echo can be generated electrically when there is an impedance mismatch, or
generated acoustically by feedback from a speaker or ear piece to a
microphone. Any echo that is ultimately returned to the IP Phone is more
noticeable to the listener because of the additional delay introduced by the IP
connection.
The Voice Gateway Media Card has echo cancellers included as part of its
function that cancels echo generated on the TDM side of the Media Gateway.
When there is audio going through the Voice Gateway Media Card, the echo
cancellers are enabled.
The IP Softphone 2050 has no echo canceller, so a slight echo from acoustic
coupling on the headset can occur in some call situations.
Clock synchronization
Buffer underruns and overruns can occur since there is no sample clock at the
receiving end of an IP audio stream synchronized to the transmitting clock.
The buffer overruns and underruns are corrected by two mechanisms, both of
which apply to the IP Phones and the DSPs on the Voice Gateway Media
Card.
IP Phones Description, Installation, and Operation