[Serusers] Rewriting URI in the Contact field

Greg Fausak greg at august.net
Fri Jan 10 19:18:00 CET 2003 

Does this scheme work with more than one ATA186 behind the
Nat firewall?

---greg


> -----Original Message-----
> From: Maxim Sobolev [mailto:sobomax at FreeBSD.org] 
> Sent: Friday, January 10, 2003 11:02 AM
> To: Greg Fausak
> Cc: 'Jiri Kuthan'; serusers at lists.iptel.org; kapitan at portaone.com
> Subject: Re: [Serusers] Rewriting URI in the Contact field
> 
> 
> On Fri, Jan 10, 2003 at 09:38:11AM -0600, Greg Fausak wrote:
> > Howdy,
> > 
> > I have a ATA186.  I may have misunderstood the COMEDIA
> > reference.  Does the ATA186 poke itself through a NAT 
> router to a SIP
> > server???
> 
> The problem is that ATA186, while de-facto is partially 
> COMEDIA-compatible
> as it always sends and receives UDP messages using the same 
> port, i.e. 5060
> for signalling and 10000 for RTP, it doesn't yet announce it 
> to the world
> by inserting a blank rport parameter into the header and couldn't be
> configured to add direction=passive into SDP. Therefore, SIP 
> server should
> be properly modified to add missed parts when it receives 
> request from ATA.
> 
> Another problem is that those symmetric schemes don't work when both
> parties are behind NATs, or when the call terminates to UA which
> doesn't support direction=active.
> 
> -Maxim
> 
> > 
> > NAT seems to be the biggest hurdle we have.
> > 
> > ----greg
> > 
> > > -----Original Message-----
> > > From: Maxim Sobolev [mailto:sobomax at FreeBSD.org] 
> > > Sent: Friday, January 10, 2003 8:58 AM
> > > To: Greg Fausak
> > > Cc: 'Jiri Kuthan'; serusers at lists.iptel.org; kapitan at portaone.com
> > > Subject: Re: [Serusers] Rewriting URI in the Contact field
> > > 
> > > 
> > > On Fri, Jan 10, 2003 at 08:27:46AM -0600, Greg Fausak wrote:
> > > > What is this device?  Where can I get one? What does it cost?
> > > 
> > > Cisco ata186 is two-port analog telephone adapter, i.e. it has two
> > > standard ports for connecting ordinary phones and one 10M ethernet
> > > port. It supports SIP and H323 (G711, G723 and G729 audio codecs)
> > > and costs some US$150.
> > > 
> > > -Maxim
> > > 
> > > > 
> > > > Thanks :-)
> > > > 
> > > > ---greg
> > > > 
> > > > > -----Original Message-----
> > > > > From: serusers-admin at lists.iptel.org 
> > > > > [mailto:serusers-admin at lists.iptel.org] On Behalf Of Maxim Sobolev
> > > > > Sent: Friday, January 10, 2003 8:15 AM
> > > > > To: Jiri Kuthan
> > > > > Cc: serusers at lists.iptel.org; kapitan at portaone.com
> > > > > Subject: Re: [Serusers] Rewriting URI in the Contact field
> > > > > 
> > > > > 
> > > > > Yes, I know - we have studied all those methods in 
> details. Our
> > > > > method of choice is symmetric signalling/symmetric media 
> > > (aka COMEDIA)
> > > > > due to the following reasons:
> > > > > 
> > > > > 1. Things should work without modifying or 
> reconfiguring existing
> > > > > user's infrastructure (NATs) and should be compatible with all
> > > > > widely-used NATs.
> > > > > 
> > > > > 2. We are bound to ata186 as UA. It is compatible with 
> > > this method.
> > > > > Support for other UAs isn't required.
> > > > > 
> > > > > 3. The calls will be terminated to Cisco GWs, while 
> > > COMEDIA support
> > > > > was recently added into Cisco IOS, so that 
> theoretically the only
> > > > > thing we need is to add received/rport support into 
> > > proxy/registrar
> > > > > and update IOS at termination points.
> > > > > 
> > > > > 4. No media relay is allowed, because this will 
> create excessive
> > > > > bandwith load in a single point.
> > > > > 
> > > > > 5. COMEDIA support is likely to become part of the 
> > > standard, so that
> > > > > our investments into development are protected.
> > > > > 
> > > > > -Maxim
> > > > > 
> > > > > On Fri, Jan 10, 2003 at 02:26:07PM +0100, Jiri Kuthan wrote:
> > > > > > There is actually a plenty of options how to traverse NATs.
> > > > > > Sadly, none of them works in all possible scenarios.
> > > > > > 
> > > > > > a) STUN -- some phones (kphone for linux, snom hardphones)
> > > > > >    have the ability to "fool" NATs to accomplish traversal
> > > > > >    using the STUN protocols; particularly good if you cannot
> > > > > >    manipulate the NAT
> > > > > > b) geek tweaks -- you have a configurable NAT and 
> configurable
> > > > > >    phones (there are some of both of them).  you 
> > > configure static 
> > > > > >    port forwarding in the NAT and phones to advertise the
> > > > > >    public address in contacts and elsewhere
> > > > > > c) ALG -- use a SIP-aware NAT such as PIX or Intertex
> > > > > > d) UPnP -- takes UPnP enables phones (snom is) and NATs
> > > > > > e) SIP/media relay -- that's a too ugly story
> > > > > > 
> > > > > > What to choose best depends on your network setting 
> -- can you
> > > > > > tweak the NAT, can you afford replacing it with a 
> SIP-enabled
> > > > > > one, are the phones you are using configurable or 
> do they use
> > > > > > STUN, do you have a server on the public or private NAT side
> > > > > > or on each of them, etc.
> > > > > > 
> > > > > > I remember someone shared with us he was using ser in his
> > > > > > network to do the translation of SIP addresses on behalf
> > > > > > ot the phones. The ser script was configured to statically
> > > > > > rewrite private IP addresses to the public address using
> > > > > > replace/textops.
> > > > > > 
> > > > > > -Jiri
> > > > > > 
> > > > > > At 01:32 PM 1/10/2003, Maxim Sobolev wrote:
> > > > > > >Folks,
> > > > > > >
> > > > > > >I need an advise on how to better implement one feature, 
> > > > > which isn't
> > > > > > >currently present in SER. We need to allow UAs behind 
> > > NAT properly
> > > > > > >register with the registrar - by "properly" I mean that 
> > > > > host:port portion
> > > > > > >of URI in Contact field should not be used, but host:port 
> > > > > the request
> > > > > > >came from should be used instead. By definition we know 
> > > > > that those UAs
> > > > > > >will support symmetric SIP signalling, so that this scheme 
> > > > > will work just
> > > > > > >fine.
> > > > > > >
> > > > > > >In my opinion there are two ways to do it: either add new 
> > > > > rewritecontact*
> > > > > > >family of functions similar to rewritehost ones. or add a 
> > > > > new flag for
> > > > > > >the save() function. This is where I need your help - 
> > > > > which implementation
> > > > > > >looks better for you (or maybe you have even some better 
> > > > > idea), since
> > > > > > >we are really interested in inclusion of our changes into 
> > > > > the mainline to
> > > > > > >reduce our local hacks.
> > > > > > >
> > > > > > >Regards,
> > > > > > >
> > > > > > >Maxim
> > > > > > >
> > > > > > >_______________________________________________
> > > > > > >Serusers mailing list
> > > > > > >serusers at lists.iptel.org
> > > > > > >http://lists.iptel.org/mailman/listinfo/serusers 
> > > > > > 
> > > > > > --
> > > > > > Jiri Kuthan            http://iptel.org/~jiri/ 
> > > > > _______________________________________________
> > > > > Serusers mailing list
> > > > > serusers at lists.iptel.org
> > > > > http://lists.iptel.org/mailman/listinfo/serusers
> > > > > 
> > > 
>

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