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North American Network Operators Group

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Re: VoIP over IPsec

  • From: Charlie Clemmer
  • Date: Mon Feb 17 10:55:58 2003


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At 01:24 AM 2/17/2003 -0600, Stephen Sprunk wrote:
>Unfortunately, IOS can introduce jitter when encrypting packets.  To
>mitigate this, you can apply QOS, with a strict priotiy queue for the VoIP
>packets and the "qos pre-classify" feature.  Your mileage will vary
>depending on the CPU power of the router, the traffic levels, and whether
>you're using hardware encryption.

Stephen, I know this is outside of Charles' original inquiry, but I'm not 
familiar with this "qos pre-classify" feature. Since we would be encrypting 
voice traffic ... at what point would you classify it? If I classify it 
before it goes into the tunnel and gets encrypted, would that 
classification last once it's encrypted? If we try to classify after it's 
been encrypted, how can we tell it's voice traffic? It seems to me that 
jitter from both the actual encryption process as well as that associated 
with basic serialization would be the potential death of VoIP in this 
scenario, but I'm not sure mechanisms available to help resolve that risk. 
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