Ask Your Question
0

Can't see RTCP REMB packets

asked 2022-01-10 18:54:36 +0000

Beans gravatar image

updated 2022-01-10 20:39:35 +0000

Hello, I'm trying to view max bitrate fields (BR Exp and BR Mantissa) in the RTCP REMB packets which are filtered as packet type value 206 (payload-specific feedback) and feedback message type value 15 on Wireshark, but I can't see any information past media source SSRC. I captured these packets during a Google Meet call using Firefox.

Here is the packet capture (meet-firefox-Jan10.pcap) and screenshot I attached in the same folder: https://drive.google.com/drive/folder...

I expected to see the RTCP packet in the message format:

 0                   1                   2                   3               
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P| FMT=15  |   PT=206      |             length            |                               
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  SSRC of packet sender                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  SSRC of media source                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Unique identifier 'R' 'E' 'M' 'B'                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Num SSRC     | BR Exp    |  BR Mantissa                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   SSRC feedback                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ...                                                          |

Note: I get an Expert Info (Warning/Protocol): Unknown Application Layer Feedback Type

Thank you so much for any help

edit retag flag offensive close merge delete

Comments

Can you share a capture, or at least display the RTCP packet?

grahamb gravatar imagegrahamb ( 2022-01-10 19:41:23 +0000 )edit

I tried attaching an image and attachment but ask.wireshark gives me an error: >60 points required to upload files..

Beans gravatar imageBeans ( 2022-01-10 19:52:51 +0000 )edit

Putting one on a publicly accessible file sharing site and posting the link to it here is the way to go.

Jaap gravatar imageJaap ( 2022-01-10 20:24:08 +0000 )edit

Ok I see, I attached a link in the post and here it is also: https://drive.google.com/drive/folder...

Beans gravatar imageBeans ( 2022-01-10 20:37:19 +0000 )edit

Hi, No one has written code to dissect https://datatracker.ietf.org/doc/html... so anything after the Aplication identifyer is unknown to Wireshark. You could write a bug request asking to have it implemented and see if someone picks it up.

Anders gravatar imageAnders ( 2022-01-11 07:14:22 +0000 )edit

2 Answers

Sort by ยป oldest newest most voted
0

answered 2022-01-11 05:43:42 +0000

Chuckc gravatar image

Example pcap attached to 9757 - Add RTCP dissector for goog-remb (Receiver Estimated Maximum Bitrate)

Analyze -> Decode As... and set Current to RTCP.

(Wireshark User Guide example of Decode As...)

edit flag offensive delete link more

Comments

Thanks for the reply, but UDP packets are already being decoded as RTP and RTCP.

Beans gravatar imageBeans ( 2022-01-11 05:53:09 +0000 )edit

Is the question how to capture REMB or how to decode and view when they are captured?

Chuckc gravatar imageChuckc ( 2022-01-11 06:13:32 +0000 )edit

I guess it's the prior.. My understanding is bandwidth estimation (specifically REMB technique) should be sent by default along with other RTP/RTCP packets when video calling over Firefox, but I don't see the REMB packets given that the SSRC of media source must be 0 (along with packet type=206 and fmt=15). Also, I attached a link with the mentioned packet capture along with a screenshot.

Beans gravatar imageBeans ( 2022-01-11 06:24:53 +0000 )edit
0

answered 2022-01-11 04:54:55 +0000

Beans gravatar image

I had overlooked to filter SSRC of media source to be 0. It seems that I did not capture any REMB packets in the captured packets.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools

1 follower

Stats

Asked: 2022-01-10 18:53:56 +0000

Seen: 425 times

Last updated: Jan 11 '22