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[Didier Barvaux <question227455@xxxxxxxxxxxxxxxxxxxxx>]

Question #227455 on rohc changed:
https://answers.launchpad.net/rohc/+question/227455

    Status: Open => Answered

Didier Barvaux proposed the following answer:
Matthew,

> So how would you go about tackling this problem, what do you think my
> options are?
>
> Do I compress just the UDP and RTP headers prior to IPSec, does that
> work? Can I do better and get compression of the IP header as well?

When using the tunnel mode of IPsec, I think that you can compress with
ROHC at your convenience before, after, or before+after protecting the
packets with IPsec.

1/ Case "before":
     IP/UDP/RTP/data -> ROHC/data -> IP/ESP/ROHC/data

2/ Case "after":
     IP/UDP/RTP/data -> IP/ESP/encrypted(IP/UDP/RTP/data)
                                      -> ROHC/encrypted(IP/UDP/RTP/data)

3/ Case "before + after":
     IP/UDP/RTP/data -> ROHC/data
                                      -> IP/ESP/encrypted(ROHC/data)
                                      -> ROHC/encrypted(ROHC/data)

Case 3 should provide you the best compression efficiency.

Cases 2 and 3 are not possible if you have to transmit packets
over IP network(s), except if you add some additional tunneling...

Regards,
Didier

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