Echo with BCM 50/analog trunk

[BingBang99]

I have a customer installed on a BCM50, 8 analog trunks, 13 I2002. I2002 are installed on Cisco switch over fiber optic link and when I ping the BCM I get 0.7 ms. When I make an internal call to an IP or digital phone I get no problems (near perfect). I've got a lot of echo when I make a call over analogue trunks. I am using the G.711 codec with a 10ms payload, echo canceller with NLP enabled, jitter correction is set to auto.

At the beginning of a call over analog trunk there is a lot of echo, something around 1 second lag, on some calls it seems to adjust itself and becomes insignificant, while other calls sometimes don't get better.

The Cisco switches have no QoS setup, might that have an impact over echo? Otherwise the timing of the calls is fine, no glitches or anything.

Thanks for the advice

 

[cook1082]

There is a known problem on BCM 50 with analog lines and ip phones getting echo.They may of came out with a patch but the bulliten from nortel said they were working on it.

 

[cook1082]

Found a new doc released 01/21/07 that says that if you add any analog lines to a BCM pre 4.0& 50 2.0 And the BCM is up and running that you need to disable and then re-enable the MBM or exp module to TUNE THE LINES.If it is a BCM 50 main unit reeboot.

 

[elturko]

Cook -- Do you have a bulletin number or could you provide a link to taht bulletin. I'm interested, as we're having the exact same problem on a new BCM 50 2.0 with 1120E IP Phones.

We've checked settings for codec and jitter buffer, and none seemed to make a difference. It seems to be the analog lines, and intercom calls are crystal clear. I also thought it may be the firmware on the phones, but it also happens on an i2050 (and as the original author notes, on i2002 as well).

Tried dis/enabling the GATM and the whole system, but that didn't seem to help either.

Any other suggestions? I'm especially interested in this, because we just put in this great new phone system and it immediately has a black mark because of the terrible echoing.

We will probably try to bring up a T7316 tomorrow to see if the issue is present on a digital set as well, or just isolated to the IP phones.

Thanks,
Matt

 

[teekow]

The doc is titled "Managing Echo on BCM and SRG Installations" and doesn't have a bulletin number. The date on the doc is 1/21/2007. It states that lines need to be "tuned" once they are connected to the CO. For lines on a expansion module, you can disable/enable the module or power cycle the expansion cabinet of the BCM50. For the onboard COTs of a BCM50, you must reboot the system for the "tuning" of those lines.

Hope this helps
Rob

 

[hawks]

I got this from one of my read me files this is for rls 1.0. I don't see anything for 2.0 except what the others have mentioned.


BCM050.106-DSP-FIRMWARE
-----------------------
1. Echo on Analog Trunks
This change will improve echo canceller performance on analog trunks with low echo return loss.

This change modifies the thresholds used for the echo canceller's doubletalk detection to tolerate gain added by the lossplan on analog trunks. The improvements in ECAN performance are in the following two areas:

1) Echo canceller training over trunks with poor echo return loss will be improved. This will result in less echo during doubletalk conditions.

2) The echo canceller's Non-Linear Processor (NLP) will transition from singletalk to doubletalk at higher energy levels from the remote speaker. This change prevents echo that persists during singletalk conditions.

Q01414710

 

[elturko]

Thanks for the info everyone.

Resetting the MBM and the BCM itself never fixed the problem. A bit more info on our problem: the echo is local -- the party we call or that calls us does not hear it, and it only lasts for the first 15-30 seconds of the call.

We did some further testing, and the line voltage seems low (only 30, not 48 where it should be). Think that could be the culprit? Looks like we have have to get the telco involved and have them check the lines.

I'll share what I find out, if anything. Please let me know if any of you uncover new info on the issue.

Thanks,
Matt

 

[teekow]

Nortel makes a "line tester" that was sent out to a lot of distributors last year. Just a simple device with 4 LEDs on it that takes several measurements when plugged into the line to help with diagnosing telco problems. Yes, low voltage, mismatching impedance, etc. will cause echo to be worse. You may want to try and get one of these testers from Nortel if you have them involved.

Hope this helps
Rob