[cisco-voip] Analog FXO PSTN audio quality complaints

[Ryan Schwab]

FYI - A bug was discovered in 15.1(2)T1. This is likely unrelated to the
tone tests failing however describe the analog quality exactly.

 

CSCth60636 - PVDM3: clipping and choppy audio during double talk

 

From: cisco-voip-bounces at puck.nether.net
[mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Ryan Schwab
Sent: March-02-11 12:50 PM
To: cisco-voip at puck.nether.net
Subject: [cisco-voip] Analog FXO PSTN audio quality complaints

 

I have users complaining of degraded PSTN audio quality over FXO ports on a
2911 h323 gateway. The problem is described as "audio cutting in and out
when both people talk simultaneously."

 

My initial suspicion is certainly  a PSTN cabling issue so I ran a few THL
tone sweep tests. When ran, I get the output below:

 

JWESRT01(config-dial-peer)#do test voice port 0/0/3 thl-sweep verbose

Original impedance 600r. Input signal level=-41dBm

 

testing 600r...... Input Signal level=-41dBm

Freq (hz), ERL (dB), TX Power (dBm), RX Power (dBm)

354        5         -6              -11

554        5         -6              -11

754        5         -6              -11

954        6         -6              -12

1154       5         -6              -11

1354       5         -6              -11

1554       5         -6              -11

1754       5         -6              -11

1954       5         -6              -11

2154       4         -6              -10

2354       4         -6              -10

2554       4         -6              -10

2754       4         -6              -10

2954       4         -6              -10

3154       4         -6              -10

3354       3         -6              -9

testing complete for 600r. ERL=5

 

testing 900r...... Input Signal level=-43dBm

Freq (hz), ERL (dB), TX Power (dBm), RX Power (dBm)

354        9         -6              -15

554        9         -6              -15

754        8         -6              -14

954        8         -6              -14

1154       7         -6              -13

1354       7         -6              -13

1554       6         -6              -12

1754       5         -6              -11

1954       5         -6              -11

2154       4         -6              -10

2354       4         -6              -10

2554       3         -6              -9

2754       3         -6              -9

2954       3         -6              -9

3154       3         -6              -9

 

ERL very low. set_impedance to 900r failed !!!.

 

 

Has anyone ran into this while performing analog tests? Does the fact that
it fails almost certainly point to an issue past the FXO port on the router?

 

Thanks for the advice!

 

-Ryan

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