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O-Ran, how to disable using udCompHdr from C-plane msg

asked 2026-05-25 20:05:43 +0000

Michael K. gravatar image

Newer versions of Wireshark had begun matching C- and U-plane messages. This fails when RU/DU is setup to use static compression (set by M-plane). In this case udCompHdr in the C-plane msg is not used and should be set to 0 (16 bit, no compression) - even when the U-plane messages in using e.g. BFP-9.

How do we turn off this matching function? It does not help to set O-RAB Fronthaul CUS preferences to BFP-9.

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There is a sample capture attached to 17874: Add I and Q sample value dissector in ORAN protocol. Can you recreate the issue with it?
If not, can you share a capture file showing the issue? (place on a public fileshare then update the question with a link to it)

Chuckc gravatar imageChuckc ( 2026-05-26 00:45:18 +0000 )edit
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answered 2026-05-26 08:45:59 +0000

Michael K. gravatar image

Just installed 4.7.0rc0 The checkbox for "Ignore compression settings from C-plane" solved the problem :-) (this option does not exist in 4.6.6)

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answered 2026-05-26 08:04:02 +0000

MartinM gravatar image

There is a dissector preference in the Uplink section called 'Ignore compression settings from C-plane', which will use the configured UL bitwidth and compression even when something else (usually 0:0) is signaled in the C-plane. The change to do this was merged 7th November 2025. I'm not sure if this is in 4.6 or not, I would normally direct people who don't build from source to download from https://www.wireshark.org/download/au.... Looking at it now, I will add 'UL to the preference label to make it more obvious.

Hope this helps, and that you were talking about U-plane in the uplink? I notice that the capture referenced by Chuck has some UL C-plane (for PRACH), but does not include the corresponding U-plane frames..

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That is exactly what I was looking for :-) However, I do not see it in O-RAN FH CUS preferences (v4.6.6-0-g3a22c3ef473d). Am I looking in the wrong place?

Michael K. gravatar imageMichael K. ( 2026-05-26 08:35:00 +0000 )edit

Just installed 4.7.0rc0 The checkbox for "Ignore compression settings from C-plane" solved the problem :-)

Michael K. gravatar imageMichael K. ( 2026-05-26 08:44:33 +0000 )edit

ORAN FH CUS: Add pref to ignore UL C-Plane udCompHdr settings

Branches - master

Wireshark 4.6.0 is now available - Date: Wed, 8 Oct 2025 19:31:59 -0700

Looks like last ORAN change to 4.6 branch was Sept 2025.

Chuckc gravatar imageChuckc ( 2026-05-26 08:46:59 +0000 )edit
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answered 2026-05-26 08:13:44 +0000

MartinM gravatar image

To make the preference clearer (i.e., only affecting UL):

https://gitlab.com/wireshark/wireshar...

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Asked: 2026-05-25 20:05:43 +0000

Seen: 92 times

Last updated: May 26

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