Audio quality UC500 - suspect low resources

[Brendan Ord]

HI all,

I am troubleshooting a UC540 where users are complaining that voice quality degrades when they have more than one simultaneous calls.  The symptom is choppy audio.

They're using a SIP provider, over a dedicated internet connection and the voice network is air gapped, and dedicated.  I've checked for the usual problems on the internet connection - packet loss, congestion etc but this is all coming up good.

When looking at a bad quality call, there are no call stats that indicate any transport-related problem.  Jitter, packet loss, delay etc are all good - both from output on the UC540 and from the phone itself.

This problem also affects internal-to-internal calls, so this disproves the ITSP or internet connection to be at fault here.

The only thing I can put my finger on is that the box is running low on memory (so low, I can't add dial-peers for instance).  Although, as far as I'm aware the RTP is processed with the onboard DSP's.  I still can't help but think the low memory is to blame; especially as the more simultaneous calls they make the worse the problem gets.  Processor sits pretty low/normal all the time, and during bad calls.

Below is the output of show memory summary;

                Head    Total(b)     Used(b)     Free(b)   Lowest(b)  Largest(b)
Processor   8602B48C   140331892   126262296    14069596      374744     2328988
      I/O    E600000    27262976     7963964    19299012    19175360    19248924

Is there anything else I should be checking?  I'm not so sure about checking DSP resources - am I able to check that this is all working properly?  Also, I don't think there is any transcoding happening on calls - at least, not with internal-to-internal calls, and the external calls may only be getting transcoded between u-law and a-law, if anything.

Thanks in advance!

Edit: Thought I'd add that the interface facing the internet is at full-duplex (faces a bridged VDSL modem).  No QoS - not required in my opinion as there isn't much chance of congestion, plus there is only voice traffic on this network.

[Brandon Buffin]

Does the issue happen with two phones plugged directly into the UC500 or are phones connected to a switch. Can you test? Wondering if the problem could be a switchport/trunk problem between the UC500 and another switch?

Brandon

[Brendan Ord]

Thanks for the reply.

The customer is using an SG300 (one of those small business Cisco managed switches), and in total there wouldn't be anymore than say ten phones.

Pretty sure all phones are connected to the switch, so I'll ask if the customer can move two phones over to the built-in switch and test again.

[Brendan Ord]

Hi,

Yes, issue happens regardless of the phones connection method - direct on UC500 switch, on the external switch and even phones which come in over the built-in IPSEC VPN (SPA's).

Thanks in advance,

[Brandon Buffin]

Interesting. RTP traffic is phone-to-phone in the case of an internal call. Only signaling traffic would traverse the UC500. Seems to point to network congestion. Can you check switchport utilization. Can you isolate the network to only two phones (remove all other phones/computers) and test? Could you source another UC500, copy the config to the new box and test to prove or disprove any problem with the hardware?

Brandon

[Brendan Ord]

Hi,

The voice network is air gapped from PC's and data, including the internet bandwidth.  So, I really don't think it's congestion in the local LAN.

I have some other UC500's kicking around but this is getting to the point of making a decision - keep throwing good money at this old system or migrate off onto something newer (and, far better).  I've already presented this option to the customer.

Thank you, I appreciate the help but it seems we're hitting brick walls with this one.  At least I can feel more confident that this isn't a DSP or memory problem with the UC500.