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I've run into a quirky RTP implementation that generates a new SSRC after 256 packets for any given flow, which causes Wireshark to treat each flow->SSRC pair as a separate stream. i.e a 60 second call will show up as 12 unique streams under Telephony->RTP->Show All Streams.

This is fine for a quick scan of stats, but is a real pain when attempting to export a stream to .au or .raw format for audio playback. Is there a way to combine these streams into one in tshark or Wireshark?

asked 16 Sep '10, 05:25

grossman's gravatar image

grossman
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From RFC 1889:

Synchronization source (SSRC): The source of a stream of RTP packets, identified by a 32-bit numeric SSRC identifier carried in the RTP header so as not to be dependent upon the network address. All packets from a synchronization source form part of the same timing and sequence number space, so a receiver groups packets by synchronization source for playback. Examples of synchronization sources include the sender of a stream of packets derived from a signal source such as a microphone or a camera, or an RTP mixer (see below). A synchronization source may change its data format, e.g., audio encoding, over time. The SSRC identifier is a randomly chosen value meant to be globally unique within a particular RTP session (see Section 8). A participant need not use the same SSRC identifier for all the RTP sessions in a multimedia session; the binding of the SSRC identifiers is provided through RTCP (see Section 6.4.1). If a participant generates multiple streams in one RTP session, for example from separate video cameras, each must be identified as a different SSRC.

So I'd say that application isn't compliant to the RFC so in principle there is nothing to be done in Wireshark to cater for it.

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answered 17 Sep '10, 11:58

Anders's gravatar image

Anders ♦
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edited 17 Sep '10, 12:20

Gerald%20Combs's gravatar image

Gerald Combs ♦♦
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Believe me, I'm not going to argue that anyone or anything should bend to accommodate this RTP implementation. I was just hoping that there was some kind of clever work around that would make life a little easier.

(20 Sep '10, 11:04) grossman

Wireshark would need a mixer functionality to handle this properly. Currently it can't.

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answered 16 Sep '10, 23:10

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Jaap ♦
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accept rate: 14%

You could export them all to separate files and then mix them in a program like Audacity.

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answered 23 Sep '10, 18:11

hmmwhatsthisdo's gravatar image

hmmwhatsthisdo
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question asked: 16 Sep '10, 05:25

question was seen: 8,846 times

last updated: 23 Sep '10, 18:11

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