1861 call quality issues

Answered Question
Jan 16th, 2009
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Hello,

I have a newb question. We have an 1861 deployed at one of our remote sites. There are 5 total IP phones and 4 analog lines connected into the FXO ports on the 1861. The 1861 is connected to a 3Meg DSL connection that runs over the same line as the fax line. When a customer calls in, there is really bad echoing and sometimes you can't understand them at all. This goes for local and long distance. What I have noticed is when there is data moving across the pipe, call quality goes way down. We did a few tests where we would call them and then copy a 10MB file to a computer located at their facility. The call quality was terrible during the copy process but got better once the copy was done. I don't understand how copying a 10MB file to a computer would affect a call coming in on an analog line. Can anyone help me with this?

Correct Answer by Nicholas Matthews about 8 years 6 months ago

Hi Troy,


Try something for me - take fair-queue off of your policy-map VOICE class-default.


-nick

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paolo bevilacqua Fri, 01/16/2009 - 08:35
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In theory it shouldn't, but copper plants are not always like theory. Anyway, why don;t you tray the FXO sweeping to see if non-default impedance settings helps ? Check this great document


http://www.cisco.com/en/US/tech/tk652/tk701/technologies_tech_note09186a0080477a06.shtml


Also gain could have a play, but would try impedance anyway.

Nicholas Matthews Fri, 01/16/2009 - 08:44
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Hi Troy,


The IP traffic shouldn't affect analog voice. You can see if for some reason the increased IP traffic is increasing the CPU utilization. 'show proc cpu hist' will help figure this out.


Otherwise - check the 'show interfaces' for the connected phones for duplex, CRC, dropped packets, etc. If you have QoS configured - turn it off.


What version of IOS are you on?



-nick

troymaki Fri, 01/16/2009 - 08:55
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Nick,

I am running version 12.4(22)T. I do not see any errors on any of the interfaces. I ran the sho proc cpu hist command and it looks like the cpu topped out around 60%. Here is a scrubbed copy of the config.


Thanks, Troy



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Nicholas Matthews Fri, 01/16/2009 - 09:05
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Hi Troy,


Try something for me - take fair-queue off of your policy-map VOICE class-default.


-nick

troymaki Fri, 01/16/2009 - 09:20
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Nick,


I have removed it. I will make some test calls and see if it helped or not. Is that command typically issued on a normal install? This router was setup by a consultant before I joined this company and I haven't been too impressed with anything else that they have done. I'll let you know how it goes.

Thanks, Troy

troymaki Fri, 01/16/2009 - 13:38
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So far so good. They have been fine for the past 3 1/2 hours. We have run multiple tests and they all went good except for the first one which I did immediately after making the change. What alerted you to have me remove fair-queue?

Nicholas Matthews Fri, 01/16/2009 - 13:47
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Hi Troy,


They changed the fair queueing queues in 12.4(22)T, and I have seen a few issues with it. To be honest, I am not a CEF expert, but it has something to do with the queue size and flow count. I think since the change, I've seen some suggestions to have it on all the time change to 'on an as-needed basis, with guidance'.


We will do FIFO queueing on links faster than 1.544 Mb/sec, and this qualifies.


Glad we could resolve this :)


-nick

Nicholas Matthews Fri, 01/16/2009 - 16:13
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For those playing the home game -


This is the more accurate description:

http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/qos_frhqf_support.html#wp1089229


It's a 12.4(20)T overhaul of QoS. The normal WFQ in fair-queue was changed to flow based. On top of that, the default queue limit was moved to 1/4 (16). In the class class-default, you could have also added something like 'queue-limit 256' to avoid this problem.


The more you know...



-nick

paolo bevilacqua Sat, 01/17/2009 - 03:52
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Great info, I still fail to understand how QoS in the ADSL spectrum influences noise in the audio portion on a phone pair, but that's just me perhaps :)

troymaki Mon, 01/19/2009 - 06:28
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Ok, the call quality is great. I am certain that removing that line fixed the issue but now, we are experiencing up to a 10 second delay when an outside caller calls in. It doesn't happen all the time, just intermittent. Is this a QoS issue again or something else?

Nicholas Matthews Mon, 01/19/2009 - 07:27
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Depends - what's the entire call flow, end to end, and which parts go over the internet/WAN?


-nick

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