Talk:SIP trunking

What is a SIP trunk in terms of SIP protocol mechanisms?
This article in its current version does a good job in describing the architectural, business and legal framework. But I am missing important information: what is a SIP trunk technically? In particular, how are SIP requests routed from the ITSP to the private domain? Does this use SIP REGISTER, DNS SRV records, etc.? Are there relevant RFCs or other standards? Thanks.

--Ehlo127001 (talk) 20:37, 14 April 2014 (UTC)