Steps To Correct Echo - MCK EXTender PBXgateway II System Administrator Manual

The local phone company may have irregular length loops, and/or amplifiers; all of which can cause
impedance irregularities. The impedance in the PBX on the trunk group facing these lines must match
the impedance of the circuits coming in from the telephone company, or power (in the form of Echo) will
be reflected back from the sender to the remote EXTender user. Normal loops should be optioned for
600 OHMs. Loops that are long, (over 3000 ft, to Central office, or long runs of copper) should be
optioned for RC (Avaya-Resistive Capacitance). RC self-adjusts to match the impedance of the loop. On
the Meridian, loops should be optioned for Balanced Impedance or Termination Impedance, depending
on the circuit.
Isolate the cause of the echo by:
1. Call within the PBX from extended phone to extended phone.
2. Make calls from extended phone to a local number outside the PBX.
3. Dial a long distance number.
Use the questions below to isolate the problem:
•
Is the echo only on calls that go to the local phone company?
•
Does the echo only happen on local calls?
•
Does the site have a T1 for long distance?
•
Do long distance calls experience echo?

Steps to Correct Echo

Ensure that your WAN settings equal the bandwidth available from your CSU.
Step 1
The echo canceller in the EXTenders must be checked. To do this, Tech Support may need dial-up
access to the extender units.
Note: It is normal for the remote user to hear some echo during the first three to five seconds of a call.
Afterwards, the echo canceller kicks in, and the echo goes away. This verifies that our echo
canceller is operating correctly.
Step 2
In most cases, if the extenders are set up properly, a simple trunk group parameter change in the PBX
will remove the cause of the echo.
You need to know which trunk group facing the local phone company is experiencing the problems. You
need to see if local outbound, long distance, or DID incoming calls are experiencing the echo, as each
type of call will route differently in the PBX. The PBX vendor should be able to change the trunk group
Ohm setting. There are usually only 2 options on trunk groups: RC, and 600 Ohm.
600 Ohm is the normal setting for a trunk group.
The RC (Resistive Capacitance) setting is used for trunk groups where the resistance is other than 600
Ohm, or for trunk groups facing the phone company. If the users are experiencing echo, RC should be
tried because it will self-adjust to match the impedance of the circuit.
Step 3
In more extreme cases, the local telephone company is needed. With their own specialized test
equipment, they need to measure the levels and compare them to engineering specifications. The levels
for 2-wire analog circuits will vary, so the circuit's specifications should be precisely determined by the
telephone company. In general, the Receive levels should be between –5 db and –10 db.
If all of the above steps do not work, then investigate NTE electronics metallic resistors (220 ohm).
PBXgateway II System Administrator's Guide 152