Datasheet

Configuring Voice Ports
Configuring Digital Voice Ports
VC-94
Cisco IOS Voice, Video, and Fax Configuration Guide
Echo Adjustment
Echo is the sound of your own voice reverberating in the telephone receiver while you are talking. When
timed properly, echo is not a problem in the conversation; however, if the echo interval exceeds
approximately 25 milliseconds, it is distracting. Echo is controlled by echo cancellers.
In the traditional telephony network, echo is generally caused by an impedance mismatch when the
four-wire network is converted to the two-wire local loop. In voice packet-based networks, echo
cancellers are built into the low-bit rate codecs and are operated on each DSP.
By design, echo cancellers are limited by the total amount of time they wait for the reflected speech to
be received, which is known as an echo trail. The echo trail is normally 32 milliseconds. In Cisco
System’s voice implementations, echo cancellers are enabled using the echo-cancel enable command,
and echo trails are configured using the echo-cancel coverage command.
To configure parameters related to the echo canceller, use the following commands beginning in
voice-port configuration mode:
Step 2
Router(config-voiceport)# playout-delay {nominal value
| maximum value | minimum {default | low | high}}
Tunes the playout buffer to accommodate packet
jitter caused by switches in the WAN.
The keywords and arguments are as follows:
• nominal—Defines the amount of playout
delay applied at the beginning of a call by the
jitter buffer in the gateway. In fixed mode, this
is also the maximum size of the jitter buffer
throughout the call.
• value—Specifies the range that depends on
type of DSP and configured codec complexity.
For medium codec complexity, the range is
from 0 to 150 ms. For high codec complexity
and DSPs that do not support codec
complexity, the range is from 0 to 250 ms.
• maximum (adaptive mode only)—Specifies
the jitter buffer's upper limit (80ms), or the
highest value to which the adaptive delay is
set.
• minimum (adaptive mode only)—Specifies
the jitter buffer's lower limit (10 ms), or the
lowest value to which the adaptive delay is
set.
• default—Specifies 40 ms.
Command Purpose