Direct incoming calls SRV problem - alternative solution

[v164]

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:

sip:userid@dyamic_dns_address

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 sipbroker.com 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:

sip:userid@dyamic_dns_address

use this SIP URI:

sip:userid@dyamic_dns_address:5060


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 sipbroker.com proxy, which introduces a further point of potential failure (such as the "lr=on" problem).