[OpenSIPS-Users] One way audio with AudioCodes Mediant 2000 and NAT

[Johansson Olle E]

10 feb 2009 kl. 13.10 skrev Iñaki Baz Castillo:

> 2009/2/10 Johansson Olle E <oej at edvina.net>:
>
>> If both devices are on private IP's, there's going to be two
>> RTP proxys involved if they're on different SIP networks.
>>
>> Each SIP service needs an RTP proxy for supporting their
>> local users.
>
> Hi, I don't fully agree on it:
>
> alice --- (NAT A) --- ProxyA & RtpProxyA --- ProxyB & RtpProxyB ---
> (NAT B) --- bob
>
> In this case, when alice calls bob, ProxyA will apply RtpProxyA so the
> SDP will contain a public IP.
> Since ProxyB knows that bob is registered behind NAT, it will try to
> apply RtpProxyB but this will "fail" because the incoming SDP contains
> a line:
>  a=nortpproxy:yes
> This line was added by ProxyA when applying RtpProxyA.
> When ProxyB executes "force_rtpproxy()" this function will not modify
> the SDP since that line is present. If not, there will be no audio
> because RtpProxyA would be waiting for audio from RtpProxyB and vice
> versa (lock condition).
On the INVITE there's no need for ProxyB to allocate an rtpproxy, since
the SDP already has public IP - fixed by Proxy A.

>
>
> ProxyB must be well configured, this means that since
> "force_rtpproxy()" didn't success on the incoming INVITE, it must no
> execute "force_rtpproxy()" on the 18X/2XX response from bob. For this,
> I use a bflag(RTPPROXY_SET) which only set to 1 if "force_rtpproxy()"
> succeded in the incoming INVITE, and only run "force_rtpproxy()" for
> responses from bob if that bflag is on.
It should force RTPproxy on teh response from Bob, since Bob is
a local user and the SDP includes a private IP.

>
>
> "force_rtpproxy()" returns TRUE (1) just in case the SDP was modified.

Yes.

/O
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