[LINK] RFC: 'Deep Packet Inspection'

[Richard Chirgwin]

Roger Clarke wrote:
> I've been asked to do a short piece explaining the implications of 
> deep packet inspection.  It's for an educated but non-technical 
> audience:
> http://www.anu.edu.au/people/Roger.Clarke/II/DPI08.html
>
> Constructive criticism gratefully received.
>
> (It's a freebee for the organisation, and is parallel-published on my 
> site under an open content licence;  so I'm not embarrassed to ask 
> for help!).
>
>   
Roger,

I'm commenting on-list so that if I'm wrong, someone will catch me out!

Regarding the inclusion of VoIP as a packet-inspection device, I'm not
so sure. In a typical configuration, a VoIP-PSTN gateway (also known as
a media gateway) is handling traffic explicitly addressed to it:
VoIP originator >> VoIP server
VoIP server identifies conversation as "off network"
VoIP server >> Media Gateway
Media gateway >> PSTN

In this sense, I would argue that the Media Gateway is the "destination
node" of the IP packets - its role is more akin to that of an SMTP
server rather than as a "packet inspector". Data is deliberately
addressed to the mail server, as the recipient of IP datagrams
containing audio in the packet payload; and the media gateway
reassembles the audio, performs a codec translation (if for example the
VoIP system is using a non-PSTN codec), and hands the traffic off to the
PSTN.

Cheers,
Richard Chirgwin