Subject: data content identification

From: "Bogdan Ghita" <[email-masked]>
Date: Thu, 18 Mar 1999 14:35:10 -0000

Hello everybody

I don't know if there is an answer to my problem, but it worth to try at
least. I am looking for a method to identify voice packets on a data stream.
Considering the level of standardisation for the IP telephony, I thought to
start, for the beginning, with standard protocol, like HTTP, and then, if
the results are encouraging, to go on with my study.

I looked through the internet and the RFCs and I haven't found any
suggestion for determining the content of the packet by any method (looking
at its header, watching the data flows going through a point, and so on). It
is not supposed to be only a port-identifying at the TCP level, because
there is no standard, yet, for using specific ports for IP telephony, so
this could be consider a dead end.

Do you have any idea how could I solve this problem?

Thank you
Bogdan Ghita

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

---

From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 18 Mar 1999 11:24:32 -0500

The media (voice) for Internet telephony is transported using RTP, which
usually runs on UDP. Unfortunately, RTP does not have its own port
number or protocol number. The protocol is that for UDP, and the port is
established dynamically via the signaling protocols (SIP/SDP or H.323).
Therefore, there is no way a router can statelessly determine that a
packet is RTP. The determination is possible by stateful means, as is
done with RTP header compression (rfc2508). You can also snoop the
signaling packets and extract the port numbers.

I had written a proposal way back when for making RTP its own protocol
for this reason
(http://www.cs.columbia.edu/~jdrosen/papers/draft-rosenberg-rtpproto-00.txt),
but there was solid consensus not to do this, since it introduces all
kinds of backwards compatibility issues.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX:   (732) 834-5379                       Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen

---------