[c-nsp] VoIP issue with a ATA186 behind a 7206 + 2950 switch

Nate Carlson natecars at real-time.com
Tue Aug 10 12:24:57 EDT 2004

Hey all,

I'm having an interesting issue with one of our customers. They recently 
signed up for Vonage, and are getting choppy calls over our network. 
Here's the layout I'm dealing with:

Cisco 7206VXR
  s3/1 - T1 to provider A
  s3/2 - T1 to provider B
  fa1/0 - 100mbit ethernet to 2950 switch
  e2/0 - 10mbit ethernet to 2950 switch
  e2/3 - 10mbit ethernet to provider C

If the ATA186 is behind the 2950 on e2/0, the calls are choppy on the
ATA186 end only. (The person on the remote end hears the person talking on
the ATA186 fine, but on the phone connected to the ATA186, you can hardly
hear what the POTS person is saying.) If it is behind the 2950 on fa1/0,
it sounds perfect both directions. Both e2/0 and fa1/0 are coming out of
the same /23 announcement to the world, so the incoming and outgoing path
should be the same for both - looks like it's going out s3/2.

I've checked to make sure we don't have any duplex mismatches, errors on
any of the involved ports, etc. Per MRTG, neither of the ethernet ports
are pushing more than 1-2mbit, so there shouldn't be an issue there. Here
are the software versions we are running:

7206: 12.0(9)S
2950 on fa1/0: 12.1(13)EA1c
2950 on e2/0:  12.1(13)EA1c

Both of the switches aren't doing anything special; the only major
difference is that on the switch on the e2/0 network, we have a couple of
the switchports set to protected, but not the one that the ATA186 is
hanging off of or the uplink to the 7206.

Any ideas on the best way to troubleshoot this problem? Thanks!

Nate Carlson <natecars at real-time.com>   | Phone : (952)943-8700
http://www.real-time.com                | Fax   : (952)943-8500

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