[linux-elitists] Re: Looking back ten years: Another Cypherpunksfailure (fwd)

[Joseph J. Tardo]

For signalling maybe, but not for RTP media streams and RCTP, read on down
to section 7.6.2.1 of PKT-SP-SEC-I05-020116.

At 08:41 AM 1/29/02 +0800, Enzo Michelangeli wrote:
>> > There are other problems with using IPsec for VoIP..  In many cases
>> > you are sending a large number of rather small packets of data.  In
>> > this case, the extra overhead of ESP can potentially double the size
>> > of your data.
>>
>> HOW small?  You'd already be adding IP+UDP+RTP headers (20 [or 40] +
>> 8 + 12 = 40 [or 60] bytes).  Using ESP with authentication would add
>> another 22, plus possible explicit IV and padding, if needed -- call
>> it 30?
>>
>> 20ms of uncompressed telephone quality data is 160 bytes ...
>
>True, but VoIP uses pretty efficient codecs, typically compressing by a
>factor of 8 (G.729) to 10-12 (G.723.1). On the other hand, the payload of an
>RTP packet may contain more than one frame (increasing the latency, of
>course: see e.g. http://www.openh323.org/docs/bandwidth.html ).
>
>Anyway, IPSEC (plus Kerberos/PKINIT) is the security mechanism chosen by the
>PacketCable initiative:
>
>http://www.packetcable.com/
>http://www.packetcable.com/specs/PKT-SP-SEC-I05-020116.pdf
>
>Enzo
>
>
>
>
>
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