Voice Recording via Span Port

Unanswered Question


Running CCM 6.1 with one remote branch. The remote branch has it's own ingress voice gateway. All phones at the remote branch connects to one 4506 switch. We have a Voice recording solution in place recording via spanning a port on the switch.

Problem is that the voice recording quality is not great via this method. At first we thought it might be the Voice recorder but last week we did the following tests:

1.Connect laptop to same spanned port, captured packets and saved them. Playback was not great (same result as with Voice recorder).

2. Connect laptop to IP Phone (span the phone port to the PC), capture packets and saved them. Playback of this was perfect.

Switch config:


monitor session 1 source vlan 100

monitor session 1 destination interface Fa2/6

Anyone seen anything like this or have some pointers?



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tprochazka Mon, 10/06/2008 - 04:01
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I would just check if switch isnt overutilized by this session, or if there are no errors on spanned ethernet interface. But it probably also occured to you...

Keith Fulcher Mon, 10/06/2008 - 05:10
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I would check to see what Codec is being used. Most recording solutions can only handle G711 and not even G722 (even though it is the same bandwidth....as a matter of fact....did you turn off the G722 advertising?)

CHRIS CHARLEBOIS Mon, 10/06/2008 - 08:37
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How many ports are you spanning and are you spanning the port or the VLAN? Could it simply be that packets are being dropped due to congestion on the span port?

CHRIS CHARLEBOIS Mon, 10/06/2008 - 10:35
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I would suggest try it while spanning a single port (like you did on the phone, but through the switch) and see what that does. It may just be an issue of overloading that one port. You can't get 22 straws into one mouth without a little dribbling.

nate-miller Mon, 10/06/2008 - 12:05
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What's the source of the poor quality? Are you missing packets? Do you duplicate packets?

WHen you span a VLAN, only do inbound packets, or you're likely to get packets both in and out- and you may end up with poor quality from that. (Taking a wild guess.)


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