I-CSCF does not have an ISC interface

Another realworld example of on the complexity of IMS - it seems we put in an ISC interface to the AS in I-CSCF DUT diagram (Figure 3.13). This should not be there and we made no reference to it in the text. Unfortunately we did not catch this one in time for the latest revision (R1).

Suprisingly no one noticed this error in either the Book Synopsis webinar we did with VON (link) or in the recent Testing for IMS Interoperability webinar that Gordon Eddy presented with Lightreading (link).

I must have fogotten to delete it when creating the diagram from the S-CSCF DUT example. Imagine all the extra work this could have created if this was a test spec given to QA. The sad thing is that this sort of thing happens all the time in real test environments.

Here is the correct image:

Comments

[Aayush]

Hi,
I-CSCF has to have an ISC interface. How else will it route incoming INVITE requests addressed to pre-configured sub-domain PSIs to the SIP-AS? Sometimes the I-CSCF sends an incoming INVITE directly to the AS, and the S-CSCF is not required in the signaling path for iFc processing. Similarly, the AS can also send requests to the I-CSCF directly.
I-CSCF and AS interaction is given in TS 23.228, Rel-8..Section 5.4.12.3 point c and Section 5.4.12.5 point c.
Thanks
Aayush