Lab Exercise: Voice Port Configuration

Lab Exercise: Voice Port Configuration

In this lab, you will configure and test router R1's FXS port using the topology you constructed in the lab exercise for Chapter 2, "Analog and Digital Voice Connections." Recall that an FXS port allows you to connect end stations, such as analog phones, fax machines, and modems, into a voice-enabled router.

Figure illustrates the lab's physical topology and IP addressing.

Lab Topology

Task 1: Configure FXS Port Parameters

In this task, you will issue commands to configure various parameters on an FXS port.

Complete these steps:

Enter voice port configuration mode for the FXS port on router R1.

To ensure the appropriate signaling type on this voice port, configure the signaling to the default value of loopstart.

Assume the analog phone connected to this voice port is located in one of several adjoining cubicles and you wish to create a distinctive ring for this phone so that the phone's user can distinguish their phone's ringing pattern from other phones' ringing patterns. Create a distinctive ringing pattern that causes the analog phone to ring for 5 seconds, be silent for 1 second, and then repeat this pattern. To make sure this change takes effect, shut down and then bring up the voice port, using the shutdown command, followed by the no shutdown command.

Assume that several thousand feet of cable separate the analog phone from the FXS port, and as a result, some electrical capacitance has built up in the line. This capacitance can lead to an impedance mismatch, thus causing echo. To help counteract this capacitance, change the impedance value of the voice port from the default value of 600r (that is, 600 purely resistive ohms) to 600c (that is, 600 ohms of impedance that contains both a resistive and a capacitive component).


At this point, you have not configured your voice-enabled routers with call routing intelligence. Therefore, you cannot place a call between the two analog phones. However, the parameters you configured in this lab will be in effect at the completion of the lab exercise for Chapter 4.

Task 2: Exercise Verification

In this task, you will verify the parameters you configured are in effect and that the FXS port is functioning properly.

Complete these steps:

To verify that the appropriate signaling, ring cadence, and impedance settings are applied to R1's FXS port, use the show voice port port_id command to view the port settings.

To verify that the voice port is functioning, lift the handset of the attached analog phone. You should hear dial tone. If you do not hear dial tone, you might need to administratively bring up the port with the no shutdown command.

To verify that the voice port can send a ringing signal at an appropriate voltage and frequency as to alert the attached analog phone, enter the test voice port port_id relay ring on command, followed by the test voice port port_id relay ring disable command.

Suggested Solution

Although your physical hardware might differ, Figure offers one solution to the preceding exercise.

Router R1's Configuration

R1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#voice-port 1/1
R1(config-voiceport)#signal loopstart
R1(config-voiceport)#ring cadence define 50 10
R1(config-voiceport)#no shutdown
R1(config-voiceport)#impedance 600c

The results of the show voice port port_id command, issued on router R1, should be similar to the output shown in Figure. Note that the shaded lines in the output reflect the parameters configured in this exercise

Figure. Router R1's show voice port 1/1 Output

R1#show voice port 1/1
FXS 1/1 Slot is 1, Port is 1
 Type of VoicePort is FXS
 Operation State is DORMANT
 Administrative State is UP
 No Interface Down Failure
 Description is not set
 Noise Regeneration is enabled
 Non Linear Processing is enabled
 Non Linear Mute is disabled
 Non Linear Threshold is -21 dB
 Music On Hold Threshold is Set to -38 dBm
 In Gain is Set to 0 dB
 Out Attenuation is Set to 0 dB
 Echo Cancellation is enabled
 Echo Cancellation NLP mute is disabled
 Echo Cancellation NLP threshold is -21 dB
 Echo Cancel Coverage is set to 64 ms
 Echo Cancel worst case ERL is set to 6 dB
 Playout-delay Mode is set to adaptive
 Playout-delay Nominal is set to 60 ms
 Playout-delay Maximum is set to 200 ms
 Playout-delay Minimum mode is set to default, value 40 ms
 Playout-delay Fax is set to 300 ms
 Connection Mode is normal
 Connection Number is not set
 Initial Time Out is set to 10 s
 Interdigit Time Out is set to 10 s
 Call Disconnect Time Out is set to 60 s
 Supervisory Disconnect Time Out is set to 750 ms
 Ringing Time Out is set to 180 s
 Wait Release Time Out is set to 30 s
 Companding Type is u-law
  Coder Type is g729ar8
 Voice Activity Detection is enabled
 Nominal Playout Delay is 60 milliseconds
 Maximum Playout Delay is 200 milliseconds
 Region Tone is set for US

 Analog Info Follows:
 Currently processing none
 Maintenance Mode Set to None (not in mtc mode)
 Number of signaling protocol errors are 0
 Impedance is set to 600c Ohm
 Analog interface A-D gain offset = -3.0 dB
 Analog interface D-A gain offset = -3.0 dB
 FXS idle voltage set to low
 Station name None, Station number None
 Translation profile (Incoming):
 Translation profile (Outgoing):

 Voice card specific Info Follows:
 Signal Type is loopStart
 Ring Frequency is 20 Hz
 Hook Status is On Hook
 Ring Active Status is inactive
 Ring Ground Status is inactive
 Tip Ground Status is active
 Digit Duration Timing is set to 100 ms
 InterDigit Duration Timing is set to 100 ms
 Hookflash-in Timing is set to 1000 ms
 Hookflash-out Timing is set to 400 ms
 No disconnect acknowledge
 Ring Cadence is User defined                                
 Ring Cadence are [50 10] * 100 msec                         
 Ringer Equivalence Number is set to 1
 InterDigit Pulse Duration Timing is set to 500 ms

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