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Re: [Question #201484]: In what situation will the rand change when decompressing


Question #201484 on rohc changed:

Sankar Malladi posted a new comment:
Hi Didier Barvaux.
Thanks for the excellent explanation. However i have a doubt regarding the 3rd bullet.

/ Scenario "RND=0 and change to RND=1":
      - at compressor: IPv4 + context(RND): 0 -> 1 => UOR-2-RTP + extension 3 with packet(RND)=1
      - at decompressor: IPv4 + context(RND)=0 => UOR-2-ID
      - when parsing extension 3, packet(RND)=1 is found, and packet is re-parsed as UOR-2-RTP

Can you please highlight or share the reference in the source code where
we compute the ip_id correctly?

Here is my understanding:
a. when 1st packet received with RND bit 1, then we have to compute and store the id_offset_ref as curr_ip_id - curr_SN
b. when 2nd packet is received with RND bit toggled to 0, then we hv to use the id_ref computed at step 1 and compute the current ip_id as id_offset_ref  + curr_SN.

pls correct my algorithm if you think there are any mistakes.


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