Re: [Opalvoip-devel] question about sip registriation code in OPAL - why use a different port on each registration?

[James V. V. <jam...@ve...>]

We use STUN and this would still be an issue. I would suggest
differentiating between separate registrars and refreshing an existing
one.  

In our case we use OPAL inside of a client that registers with OpenSER.
What we discovered is that OPAL refreshes it's registration at something
like 90% of the refresh window, which is fine.  Where we have problems
is that by using a new port OpenSER decides that this refresh is
actually a new contact instead of a refresh of an existing one.  This
makes sense to me as a user behind NAT that happens to want two SIP
devices to register with a registrar (for the same AOR) would have them
coming from different ports.  Only a registration of the same contact on
the same port should be a refresh.  The end result is that for some time
OpenSER has two different contacts to "dial" for an AOR.

We  have since made the change to OPAL to keep it on the same port for
registration and have had much better results.  I suspect this problem
would happen with most registrars.

I did not write our patch so I don't know if it differentiates between a
refresh and a new registrar (and the patch is opal 2.3.1), but we can
package it up if the approach I am outlining here makes sense.  If I am
full of baloney I would like to hear that too.  ;-)

Sorry for the really late response - lots of travelling lately.


-James




-----Original Message-----
From: Craig Southeren [mailto:cr...@po...] 
Sent: Monday, April 14, 2008 11:18 PM
To: Robert Jongbloed
Cc: James Van Vleet; opa...@li...
Subject: Re: [Opalvoip-devel] question about sip registriation code in
OPAL - why use a different port on each registration?

..deleted

>>
>> We might end up with our registration refresh staying on the same
>> port.
>> The question is why it is here in the first place?  Is there an issue
>> we
>> are not aware of requiring the new port?  A danger lurking here?

This is to allow operation behind symmetric NAT which will enforce a 1-1

relationship between the external appearance of the UDP port and 
registrar port

Using different local ports for each registrar will force a separate NAT

mapping for each external registrar, whereas, using the same port for 
multiple registrars will require cone NAT or unrestricted access to work

correctly.

I think a good case could be made to use separate ports for each 
registrar only when STUN is in use...

I'd be interested on opinions from others.

    Craig

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  Craig Southeren          Post Increment - VoIP Consulting and Software
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