Subject: [IPTEL] Re: RTP measuring

From: S_S_Dinesh/India/[email-masked]
Date: Mon, 8 May 2000 14:10:31 +0530

--> Bogdan Ghita writes:
>I have three questions related to RTP/RTCP.

RTP related questions should be asked on the AVT working group's list
[email-masked].

>1. Are there any  tools for monitoring RTP/RTCP (free or commercial)? I
>am interested especially in RTP analysis, and not RTCP parsing. And, if
>there are, which are their capabilities?
>In order to restrict the range of replies, I must mention that I've
>already found:
>- Hammer VoIP Test System - analysing all the parameters (drop packets,
>jitter, delay) within a VoIP call
>- HP Internet Advisor - similar
>(for these two commercial packages, I couldn't get more information
>about what actually is monitored)
>- rtpmon, which is free, but, in spite of its name, it is an RTCP
>monitor.
>
>2. Can anybody explain me what is the structure of a compound RTCP
>packet? I know, from the RTP specification, that it looks like this:
>
>if encrypted: random 32-bit integer
>|
>|[------- packet -------][----------- packet -----------][-packet-]
>|
>| receiver reports chunk chunk
>V item item item item
>--------------------------------------------------------------------
>|R[SR|# sender #site#site][SDES|# CNAME PHONE |#CNAME LOC][BYE##why]
>|R[  |# report #  1 #  2 ][    |#             |#         ][   ##   ]
>|R[  |#        #    #    ][    |#             |#         ][   ##   ]
>|R[  |#        #    #    ][    |#             |#         ][   ##   ]
>--------------------------------------------------------------------
>|<------------------ UDP packet (compound packet) --------------->|
>#: SSRC/CSRC
>
>The question is, as I couldn't understand the figure: how is the above
>figure packetised in UDP packets (is it 'line-by-line') ?

The random prefix (if any) is put at the start of the UDP packet, then
the RTCP packets comprising the compound are concatenated into a single
UDP packet.

>3. Are there any standards for encrypting RTP/RTCP (in relation with
>H.323) ? Besides inserting the 32-bit integer in the RTCP packet and
>using DES there is nothing else specified.

The a/v profile (RFC1890) allows for any encryption algorithm to be used,
with the algorithm identifier being prefixed onto the encryption key
followed by a "/" character. One can also use IPsec.

Colin

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