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[Didier Barvaux <question263736@xxxxxxxxxxxxxxxxxxxxx>]

Question #263736 on rohc changed:
https://answers.launchpad.net/rohc/+question/263736

    Status: Open => Answered

Didier Barvaux proposed the following answer:
Hello,

> I have another question concerning the optimization of the library.
> Indeed, the compression of IPv6 use less CPU charge than the
> compression of IPv4. The header of IPv6 packet (40 bytes) is longer
> than the header of IPv4 packet (20 bytes) and i send the same size
> of packets at the same speed. Is it normal? Is ROHC library more
> optimized for IPv6 packets than IPv4 packets?

I don't think the ROHC library is more optimized for IPv6 streams than for IPv4 streams. I mean, there was no specific optimization work performed for IPv4 streams that was not done for IPv6. However, I see at least 2 reasons for the speed difference:
1/ The IPv4 header includes a checksum that the compressor verifies and that the decompressor computes when building the decompressed IPv4 header.
2/ The IPv4 header includes an identification field called IP-ID that requires additional code and processing time. IPv6 does not include such a field.

If IPv4 performances are problematic, I see nothing to do for 2/.
However 1/ could be optimized by computing partial checksums only on the
fields that changed between packets.

What is the difference of performances between v4 and v6?

Regards,
Didier

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