[Serusers] Rewriting URI in the Contact field

Maxim Sobolev sobomax at FreeBSD.org
Fri Jan 10 18:01:32 CET 2003 

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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