[Serusers] rtpproxy question

[Klaus Darilion]

I like Maxims idea of inserting a flag in the SDP body most, because it
seems to be easy to implement. The drawback is that all SIP providers
have to support it - but this problem also occours with the other
solutions.

regards,
klaus

> -----Original Message-----
> From: Jan Janak [mailto:jan at iptel.org] 
> Sent: Monday, November 03, 2003 7:11 PM
> To: Klaus Darilion
> Cc: Maxim Sobolev; serusers at lists.iptel.org
> Subject: Re: [Serusers] rtpproxy question
> 
> 
> I think the solution is to modify the RTP proxy. The RTP 
> proxy should be
> symmetric only for user agents that belong to the domain of the proxy
> and if the other direction is a foreign user, it should send 
> the data to
> the IP taken from SDP and not wait for any incomming packets.
> 
> Let's take iptel.org as a hypothetical example:
> 
> If both caller and callee have iptel.org as their domain, the 
> RTP proxy
> will work as usual.
> 
> If caller is not from iptel.org but callee is, then the SIP proxy will
> pass IP of the NAT box (known from Contact in usrloc) and IP 
> from SDP of
> INVITE to RTP proxy. The RTP proxy will be symmetric for the 
> NAT IP and
> non-symmetric for the IP from SDP.
> 
> In the reverse direction, i.e. when callee is not from iptel.org and
> caller is (i.e. the invite is coming from iptel.org to fwd, for
> example), the SIP proxy will pass IP from the received 
> parameter for the 
> "symmetric side" and IP from SDP of 200 OK for the 
> "non-symmetric part".
> 
> That way it is not ensured that there is just one RTP proxy 
> along the path,
> but it should work.
> 
> In other words, every SIP proxy provides "symmetric RTP proxy" for its
> users only, it doesn't provide it for foreign users.
> 
> Drawback of this approach is that it is not possible to use 
> only one RTP
> proxy in cases like:
> 
> UA---NAT---Sipphone---iptel.org---NAT---UA
> 
> In that case both Sipphone and iptel.org must enforce RTP proxy, each
> proxy is responsible for getting their users through NAT.
> 
> Anyway, implement and deploy something like that is quite complex.
> 
>   Jan.
> 
> On 03-11 18:49, Klaus Darilion wrote:
> > But if UA1 ist not behind NAT, proxy 2 should activated its 
> rtpproxy to
> > enable a communciation although there are more than 2 Via headers.
> > 
> > I guess there is no solution yet which will work in all 
> scenarios as one
> > SIP proxy will never know the NAT-traversal strategy of 
> other proxies.
> > 
> > regards,
> > klaus
> > 
> > > -----Original Message-----
> > > From: Maxim Sobolev [mailto:sobomax at portaone.com] 
> > > Sent: Monday, November 03, 2003 6:40 PM
> > > To: Jan Janak
> > > Cc: Klaus Darilion; serusers at lists.iptel.org
> > > Subject: Re: [Serusers] rtpproxy question
> > > 
> > > 
> > > There is another possible solution: modify nathelper to only 
> > > apply RTP 
> > > proxy redirection if there is only one Via in the 
> request. This will 
> > > ensure that in the situation when there are multiple SIP/RTP 
> > > proxies in 
> > > the path only first one will handle RTP. Unfortunately it 
> > > will not help 
> > > if there are any SIP B2BUAs on the way.
> > > 
> > > -Maxim
> > > 
> > > Jan Janak wrote:
> > > > On 03-11 19:18, Maxim Sobolev wrote:
> > > > 
> > > >>Klaus Darilion wrote:
> > > >>
> > > >>
> > > >>>Hi!
> > > >>>
> > > >>>As the RTP relaying does not work with 2 RTP proxies, how 
> > > can a proxy 
> > > >>>detect
> > > >>>if the RTP stream is already redirected to an RTP proxy?
> > > >>>
> > > >>>My problem is the following scenario:
> > > >>>
> > > >>>UA1   --NAT--   SIP proxy 1   --   SIP proxy 2   --NAT--   UA2
> > > >>>               rtpproxy1          rtpproxy2
> > > >>>
> > > >>>UA1 invites UA2. SIP proxy 1 detects that UA1 is behind 
> > > NAT and enables the
> > > >>>rtpproxy1 and forwards the invite to SIP proxy2. SIP proxy 
> > > 2 knows that UA2
> > > >>>is also behind NAT. Usually, SIP proxy 2 would activate 
> > > the rtpproxy2, but
> > > >>>in this case this would not work as there is already an 
> > > rtpproxy involved.
> > > >>>How can the SIP proxy 2 detect that the IP address in the 
> > > SDP is the IP
> > > >>>address of an RTP proxy?
> > > >>>
> > > >>>
> > > >>
> > > >>Known problem. I think that I'll modify nathelper, so that 
> > > >>force_rtp_proxy() will insert some flag into the SDP body, 
> > > which will 
> > > >>tell other proxies along the request route that there is no 
> > > need to put 
> > > >>another RTP relay into the RTP path.
> > > > 
> > > > 
> > > >   Another option would be to insert a header field telling 
> > > that another
> > > >   RTP proxy is being used already.
> > > > 
> > > >   The problem is that both solutions (header field and SDP 
> > > flags) will
> > > >   be not interoperable.
> > > > 
> > > >   Another option would be to modify the RTP proxy so 
> that it will be
> > > >   symmetric only for user agents that belong to the domain 
> > > of the proxy.
> > > >   That would probably complicate things a bit.
> > > > 
> > > >     Jan.
> > > > 
> > > > 
> > > 
> > > 
> > > 
> 
>