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[Didier Barvaux <question86663@xxxxxxxxxxxxxxxxxxxxx>]

Question #86663 on rohc changed:
https://answers.launchpad.net/rohc/+question/86663

Didier Barvaux proposed the following answer:
Hello,

The library was modified in 2010 to be conform to CRC-STATIC / CRC-
DYNAMIC. The fix was first released in the 1.3.0 release in March 2010.

You may look at the related code at different locations:
* https://github.com/didier-barvaux/rohc/blob/master/src/comp/rohc_comp_rfc3095.c#L6084
* https://github.com/didier-barvaux/rohc/blob/master/src/common/crc.h#L477

All library releases since the 1.3.0 releases support CRC-STATIC / CRC-DYNAMIC, except for the "Note" found in §5.9.2 of RFC 3095    (https://tools.ietf.org/html/rfc3095#section-5.9.2) :
   Note: Whenever the CRC-STATIC fields change, the new saved CRC state
   after 1) is compared with the old state.  If the states are
   identical, the CRC cannot catch the error consisting in the
   decompressor not having updated the static context.  In U/O-mode the
   compressor SHOULD then for a while use packet types with another CRC
   length, for which there is a difference in CRC state, to ensure error
   detection.

This check and the consequence on the packet type decision are not
implemented yet. It is planned for the future release 2.4.0 : https
://rohc-lib.org/developer/roadmap/#roadmap-main-branch

Regards,
Didier Barvaux

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