Originating and terminating triggering in IMS (January 18, 2008)

Everyone making even a short insight into 3GPP’s IMS specifications could notice the significant amount of “free space” left by committee for considering different implementation approaches. Release 7’s 24.229, for example, says nothing about the way to detect originating and terminating triggering by SIP application server, when triggered by S-CSCF over ISC. Usually it is implemented using the parameters in the Route header and different IMS cores are doing this in different ways.

Fraunhofer FOKUS’ OpenIMS Core does simple:

and d here stands for “direction”: originating or terminating.

Huawei’s IMS Route headers look more sophisticated:

ORIGLGID points us to the originating leg here.

And Motorola’s IMS is my personal favorite:

Note that IMS core here informs application server, not itself about the triggering direction. This is what I call developer oriented approach.