In this mode of VoLTE service deployment, ATCF/ATGW and EATF functionalities are performed by the Access SBC. In this deployment, ATCF inter-works with P-CSCF/I-CSCF and EATF inter-works with E-CSCF where ATCF/EATF is co-located with SBC along with an external P-CSCF.
As per 3GPP specification, ATCF/EATF is invoked after P-CSCF. As part of the registration procedure, P-CSCF decides whether to invoke ATCF/EATF or not based on the criterion that is local to P-CSCF. Once ATCF/EATF is invoked, ATCF/EATF is invoked both for originating calls from UE and incoming calls towards UE. However, in this deployment, ATCF/EATF functionalities are invoked before P-CSCF (as the P-CSCF component is external).
The following topics are included in this section:
Overview
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