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[Didier Barvaux <question194142@xxxxxxxxxxxxxxxxxxxxx>]

Question #194142 on rohc changed:
https://answers.launchpad.net/rohc/+question/194142

    Status: Open => Answered

Didier Barvaux proposed the following answer:
Hello,

> First let me start by saying this is a very organized effort and
> the code your writing is excellent, thank you much for it.

:-)

> I am interested in compressing headers for RTP traffic between
> two SIP servers and I thought I could do this using the rohctunnel
> but it seems I have no benefit. While I see the traffic in the traces
> and the calls flow just fine, I see no bandwidth savings if I compare
> a call in the ROHC tunnel to a call outside of the tunnel.
>
> I seem not to match the RTP profile but I am getting matched on
> the UDP profile but no drop in bandwidth used.
> 
> Might someone have a second to point out what I am doing wrong?

The ROHC library does not detect RTP streams on the fly. It relies on
a static list of UDP ports that are considered as RTP. This is not very
reliable nor convenient. This will be reworked in the near future, 
someone is working on this topic.

Currently the list can be modified in source code. For the 1.3.x branch, see
http://bazaar.launchpad.net/~didier-barvaux/rohc/1.3.x/view/head:/src/common/rohc.h#L402
For the trunk, see http://bazaar.launchpad.net/~didier-barvaux/rohc/main/view/head:/src/comp/c_rtp.c#L40

You have to re-build the library for the change to take effect.

Notes:
 - The ROHC tunnel application is not ready for production use. However it is very
    useful for testing.
 - The ROHC tunnel application uses UDP to encapsulate ROHC packets, this is a
    great choice for easy testing, but not the best choice for best performances.
    IP encapsulation would be better (8 bytes less for every packet).


Regards,
Didier

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