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[Cedric Baudoin <question195843@xxxxxxxxxxxxxxxxxxxxx>]

Question #195843 on rohc changed:
https://answers.launchpad.net/rohc/+question/195843

Cedric Baudoin proposed the following answer:
Yes for the user plane it has to be considered. Be careful however if you
want toi group pk, since it Will have impacts on the perf (jitter and delay
)
Br
Cédric
Le 5 mai 2012 13:55, "Didier Barvaux" <question195843@xxxxxxxxxxxxxxxxxxxxx>
a écrit :

> Question #195843 on rohc changed:
> https://answers.launchpad.net/rohc/+question/195843
>
> Didier Barvaux posted a new comment:
> Cédric,
>
> > Using ROHC for that purpose implies that your 2 end points are able to
> communicate using
> > ROHC packets, that is not > straighforward (use of IP tunneling is not
> really useful if your
> > objective is to reduce overhead) . In addition, the main part of the
> overhead is due to the
> > rich text part (plain text XML) and not the header part.
>
> You're right for the modifications of the 2 end points and for the
> overhead in the signalling packets (SIP). However, for data packets
> (RTP), the overhead is still the header part. For those packets, ROHC
> may be interesting even if IP tunneling is required.
>
> Gain for ROHC without tunneling:
>  - non-compressed IPv4/UDP/RTP packet = 20-byte IPv4 header + 8-byte UDP
> header
>    + 12-byte RTP header + 40-byte audio data = 80 bytes
>  - ROHC-compressed IPv4/UDP/RTP packet = 1-byte ROHC header + 40-byte audio
>    data = 41 bytes
>  = 49% gain
>
> Gain for ROHC with IPv4 tunneling:
>  - non-compressed IPv4/UDP/RTP packet = 20-byte IPv4 header + 8-byte UDP
> header
>    + 12-byte RTP header + 40-byte audio data = 80 bytes
>  - ROHC-compressed IPv4/UDP/RTP packet in IPv4 tunnel = 20-byte IPv4
> header for
>    tunnel + 1-byte ROHC header + 40-byte audio data = 61 bytes
>  = 24% gain
>
> A 24% gain is still interesting, but the IPv4 tunnel degrades the
> compression gain.
>
> We may group several ROHC packets together (packing) to reduce the overhead
> introduced by the IPv4 tunnel:
>  - 4 non-compressed IPv4/UDP/RTP packet = 4 * (20-byte IPv4 header +
> 8-byte UDP header
>    + 12-byte RTP header + 40-byte audio data) = 320 bytes
>  - 4 ROHC-compressed IPv4/UDP/RTP packet in IPv4 tunnel = 20-byte IPv4
> header for
>    tunnel + 4 * (1-byte for packing + 1-byte ROHC header + 40-byte audio
> data) = 188 bytes
>  = 41% gain
>
> A 41% gain is definitely  interesting :)
>
>
> Regards,
> Didier
>
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