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Re: [Question #219552]: rohc 1.5.1 does not compress VoIP


Question #219552 on rohc changed:

    Status: Answered => Open

Florent Bertero is still having a problem:

Hello Didier,

Thanks for your quick reply.

I use iftop and my router as 2 different tools to mesure outgoing bandwith in 2 different cases.
    - When the tunnel is up and my call goes through the tunnel.
    - When the tunnel is down and my call goes directly to my voip switch.
In those 2 situations, I get the same results.

How can I tell my library to use RTP profiles?

Apart from the tunnel, what other way to compress rtp do I have?

Thanks again for your help.


> To: flo.bertero@xxxxxxxxxx
> From: question219552@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [Question #219552]: rohc 1.5.1 does not compress VoIP
> Date: Sun, 20 Jan 2013 09:31:04 +0000
> Your question #219552 on rohc changed:
> https://answers.launchpad.net/rohc/+question/219552
>     Status: Open => Answered
> Didier Barvaux proposed the following answer:
> Hello Florent,
> > I am using rohc 1.5.1 on 2 servers Centos 4.x and 5.x.
> > I installed from sources following your wiki and tunnel is up
> > with data transfer OK.
> >
> > It seems to be working fine but I need rohc to compress
> > RTP flow, so I set up a tunnel on 2 asterisks and created a
> > sip trunk in this rohc tunnel.
> Fine. Please note that the tunnel application is for testing purposes
> only. Do not use it on production.
> > However, I need to verify rohc's compression rate.
> > Thus, I used 2 different tools to monitore bandwidth: iftop and
> > a router calculating BP stats.
> >
> > My problem is that a call going through rohc takes as much BP
> > as a non compressed one (about 30kb/s).
> > I tried up to 3 calls and no difference were noticed.
> >
> > Compression logs during call shows that it is working:
> > 206 O-mode SO 60 28 36 4 0
> The logs show that ROHC compression is effective. On packet #206,
> you saved 24 bytes for example. It could probably be better if you
> configure the ROHC library to detect your RTP streams among all UDP
> streams.
> How do you compute the bandwidth rate with iftop and your router?
> My guess is that you take into account the IP/UDP headers of the
> tunnel in your computation.
> As said before, the tunnel application is not for production use, but
> only for testing. The overall gain (ROHC compression then IP/UDP
> encapsulation) is not that great!
> Regards,
> Didier
> -- 
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