Subject: Re: data content identification

From: "Bogdan Ghita" <[email-masked]>
Date: Fri, 19 Mar 1999 17:13:42 -0000

>> > I am looking for a method to identify voice packets on a data stream
>
>It would seem to be straightforward to look for long-lived flows at
>roughly voice-sized constant data rates.  No matter what protocol is
>being used to carry these flows, they should stick out pretty clearly.
>(As long as no one is doing crazy "spread spectrum" stuff across the IP
>port space).  Constant bit rate encoders will be easier to find than
>variable bit rate encoders, and if someone is doing streaming media like
>realaudio or video you might be confused by those.
I thought about looking at the encoders, but, again, there is no standard,
and, as you say, I cannot separate a voice conference from a live video
transmission, for example. Still, there should be something specific about
the voice (hopefully)...
>
>It'll be harder to pick out voice the less it is real time - a "push to
>talk" scheme running over any of the internet "chat" protocols will be so
>much more bursty than the canonical H.323 application than it might as
>well be a totally different beast for content identification purposes. And
>you know that the people hacking voice over chat don't go to international
>standards committee meetings very often....
Yes, that is true; the voice traffic doesn't have to be constant, or at a
constant speed.
 And I have to admit that a 'hacking voice conference' would be very useful
to my project, because it could clarify some of the aspects I'm looking for.

Regards
Bogdan Ghita

>
>--
>Edward M. Vielmetti                                 ||        ||
>Consulting Engineer, Office of the CTO,             ||        ||
>Cisco Systems                                      ||||      ||||
>Ann Arbor, MI                                  ..:||||||:...:||||||:..
>mailto:[email-masked]                      C i s c o S y s t e m s
>

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This message came from the IETF IPTEL Working Group Mailing List.

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From: Bob Bell <[email-masked]>
Date: Fri, 19 Mar 1999 10:35:06 -0700

Maybe the simplest method would be to look to the RTP headers. This should
identify the packet types for you so that you can scan them at your leisure.
This only applies to those forms of VoIP which encapsulate in RTP but that
should be a significant number of them.

>This message came from the IETF IPTEL Working Group Mailing List.

Bob Bell
Distinguished Member of the Technical Staff
Cisco Systems Inc.
801-294-3034(v)
801-294-3023(f)

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From: Robert Wood <[email-masked]>
Date: Fri, 19 Mar 1999 13:26:04 -0500

Bob Bell wrote:
> 
> Maybe the simplest method would be to look to the RTP headers. This
> should identify the packet types for you so that you can scan them at
> your leisure. This only applies to those forms of VoIP which
> encapsulate in RTP but that should be a significant number of them.
> 
	And  how do you do this as RTP  doesn't have a protocol ID?

[\] Robert Wood   

The St. Lawrence river - fresh, warm, visible diving.

mailto:[email-masked] http://www.magma.ca/~rgwood/

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