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New Member

Background Noise on WAN Calls


We have installed the following solution:

A remote Router 3825 with an ISDN PRI PSTN Link that connects through the WAN (Dedicated Link) to another 3825 at the local site.  On the local site we have a Call Manager 4.2(3), IP IVR 4.0(4) and IPCC 7.2(5).  The calls are being routed correctly from the remote site, through the WAN to the IP IVR and the IVR message is heard perfectly, but when the call gets transfered to an agent, there is a loud background noise (heard only by the caller, not the agent), which happens randomly.  If the agent puts the call on hold, and resumes it right away, the background noise goes away.

The dial-peer configuration on the remote router are as follows:

dial-peer voice 1000 voip

translation-profile outgoing XXXX

preference 1

destination-pattern 2529....

voice-class codec 1

voice-class h323 1

session target ipv4:IP Address of the Call Manager

dtmf-relay cisco-rtp h245-signal h245-alphanumeric

voice class codec 1

codec preference 2 g729br8

codec preference 3 g729r8

voice class h323 1

  h225 timeout tcp establish 3

If I disable VAD the background noise is heard only when the agent speaks.  Again, if the agent puts the call on hold and resumes, the noise goes away.

Thanks for your support.

Everyone's tags (3)

Background Noise on WAN Calls


At first blush, this sounds like a DSP bug in the router or the phone. 

What IOS version are you running?

Does the issue always occur?  Is there different behavior if you answer with speakerphone, headset, or handset?


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New Member

Background Noise on WAN Calls

Hello Steven,

Thanks for your reply. 

The IOS on the remote router is 12.4(22)T5 and 12.4(22)T on the local router. Also we have configured Media Resources configured on the Call Manager Cluster.

The issue happens a few times a day with a random behavior.  I will try to check the issue with speakerphone and handset, until now I have only tried with headset.


Background Noise on WAN Calls


Putting a call on hold and then resuming actually re-establishes the RTP stream between the two endpoints.  If it seems to happen randomly, then perhaps you need to look at your QoS and jitter.  It is possible you are dropping packets or they are getting delayed.  Check your call volume when it occurs, I'd guess that busy-hour of the day is likely when it occurs.

While I cannot reference any particular bug in 12.4(22)T or T5 that would be  affecting you, I can say it has not been my favorite IOS for voice.  If  you have 512MB of DRAM in your two 3825 routers (or can add DRAM to bring them up to that level), I'd highly suggest  moving to the latest 15.0(1)M release.  I've had very good results using that IOS with customers who have a high call volume (12,000 calls a day) and have been running it for over a year now with no issues.


P.S. When I wrote this 15.0(1)M7 was the latest release.

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New Member

Background Noise on WAN Calls


I tried with speakerphone, headset and handset with no luck, same behavior.

Unfortunaley we do not have enough DRAM to upgrade to 15.0(1)M.  Do you suggest any other IOS?

Cisco 3825 (revision 1.1) with 224256K/37888K bytes of memory.

2 Gigabit Ethernet interfaces

79 Serial interfaces

2 Serial(sync/async) interfaces

3 Channelized/Clear E1/PRI ports

8 Voice FXO interfaces

DRAM configuration is 64 bits wide with parity enabled.

479K bytes of NVRAM.

126976K bytes of ATA System CompactFlash (Read/Write)