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[Didier Barvaux <question162063@xxxxxxxxxxxxxxxxxxxxx>]

Question #162063 on rohc changed:
https://answers.launchpad.net/rohc/+question/162063

    Status: Open => Answered

Didier Barvaux proposed the following answer:
OK, I understand your question now.

The following profiles are availables:
 - the "RTP profile" that compresses/decompresses IP/UDP/RTP headers,
 - the "UDP profile" that compresses/decompresses IP/UDP headers,
 - the "UDP-Lite profile" that compresses/decompresses IP/UDP-Lite headers,
 - the "IP-only profile" that compresses/decompresses IP headers,
 - the "Uncompressed profile" that compresses/decompresses non-IP headers or fragmented IP headers.

For all the above profiles, the IP header may be IPv4 or IPv6. Up to 2
IP headers are also accepted: IPv4/IPv4, IPv4/IPv6...

There is no profile that compresses/decompresses UDP headers but not IP
headers. Not in IETF RFCs nor in the library. However it should be
possible to define one.

For your encapsulation problem (136 bytes = 3 ATM cells with AAL5
trailer, isn't it?), you may use ROHC padding or use the "jamming"
algorithm that the library implements. If that algorithm is enabled the
compressor chooses the largest ROHC packet possible according to the
configured packet size (eg. 48 bytes for ATM) and adaptation
header/trailer size (eg. 8 bytes for AAL5). This way, the remaining data
in your transmission unit is used to transmit larger ROHC packets and
thus provide better robustness against network problems.

In order to use the "jamming" algorithm, set the 2nd parameter of the
rohc_alloc_compressor() function to 1 and define the next 2 parameters
to 8 and 48. See
http://www.tech.viveris.com/docs/rohc/group__rohc__comp.html#g721fd34fc0cd9e1d789b693eb6bb6485
for documentation.

Regards,
Didier

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