Cisco Single reach number to cell phone noise issue

[faisalabdi]

Several of my users are complaining about hearing a "loud noise (sounds like a modem picking up)" when an external person places a call to the campus and the VoIP system  using Single Number Reach (SNR) forwards to their cell phone.  The problem started about 3 months ago and it is getting worse.  All the user have company provided iphone 5s.  The 'loud noise" usually happens after 5 minutes and it seems to happen to the some users more than others.  I get dozens of calls each day but I have only had it happen to me once.  

We are running CUCM 10.5 . We use PRI for connectivity to the PSTN.  Is this a internal VoIP issue, a gateway DSP issue, PRI service provider issue or wireless cellphone issue?  Any body else seeing this same or like issue?

[Terry Cheema]

Have you tried to narrow it down to a particular gateway? Or it happens for calls going through multiple gateways? Any changes (upgrades/IOS upgrades etc.) that were done in the same period?

Is it affecting people in a particular geographic area, building, or all? Random or happens all the time?

-Terry

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[Amit Sharawat]

Hi Faisal,

In SNR, there is no RTP flow through the IP network. The call is hair-pinned through 2 ports( B-channels) on the gateway.

So, you need to take PCM captures on both the B-channels a to check if it is a gateway issue or the provider issue. Link to collect PCM captures:

http://www.cisco.com/c/en/us/support/docs/voice/h323/116078-technologies-technote-commandreference-00.html

You can ask TAC to decode the captures for you or else you can do it yourself by following the instructions in the following documents:

http://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-communications-system/115749-analyze-pcm-data.html

Please rate if helpful.

~Amit