rohc team mailing list archive

[Didier Barvaux <question219566@xxxxxxxxxxxxxxxxxxxxx>]

Question #219566 on rohc changed:
https://answers.launchpad.net/rohc/+question/219566

Didier Barvaux proposed the following answer:
> 1. The offset IP-ID encoding in RFC 3095 section 4.5.5
> "When receiving a compressed packet m, the decompressor calculates
>       Offset_ref = ID_ref - SN_ref, where ID_ref and SN_ref are the
>       values of IP-ID and RTP SN in the reference header, respectively."
> 
> so here ID_ref is nothing but the IP ID that decompresser decoded
> successfully in the previous packet? but then it conflicts with the
> statement "The Offset IP-ID decoded at step a/ is not used."

This one is not correct.


> 2. [d_generic.c:7193 parse_extension3()] 16 bits of outer IP-ID in
>      EXT3 = 0x136f
> Does this mean, the IP ID has to be sent in the EXT 3 FIELDs when
> RND changed to 0 so that we donot need to look at the ip id
> decompressor decoded in prev packet?

The trace is not fully accurate. One should read: "16 bits of
W-LSB-encoded IP-ID Offset for outer IP header in EXT3 = 0x136f".
So, a/ the library W-LSB-decodes the 0x136f value to retrieve the Offset
IP-ID, then b/ the library adds the Offset IP-ID to the current SN to
retrieve the decoded IP-ID value.

Regards,
Didier

-- 
You received this question notification because you are a member of ROHC
Team, which is an answer contact for rohc.