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Unread 05-03-2007, 02:01 AM   #1
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Default Direct incoming calls SRV problem - alternative solution

DracoFelis has written this article on accepting incoming SIP calls direct to your SIP device:

"How to accept direct inbound calls to your LinkSys/Sipura adapter, bypassing all VoIP providers."
SIP Broker Wiki : Inbound Calls Directly to your LinkSys or Sipura

The method involved uses the SIP URI:


However, as described in the article, this won't work with some SIP proxies that require an SRV record. The solution presented is to use a SipBroker alias, so that the incoming call comes in via SipBroker. (The SIP proxy happily uses an A record if there is no SRV record.)

I've been reading through RFC 3261 (SIP), and the referred-to RFC 3263 (locating SIP servers), and I think I've found an alternative solution:

Instead of using the SIP URI:


use this SIP URI:


From RFC 3263:
This is a change from RFC 2543. Previously, if the port was
explicit, but with a value of 5060, SRV records were used. Now, A
or AAAA records will be used.
(ie, even if your SIP device is listening on the standard port 5060, specifying the port forces the SIP proxy to use A records rather than SRV records).

This solution, I think, could be more reliable than going via the proxy, which introduces a further point of potential failure (such as the "lr=on" problem).
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