Described herein are techniques, devices, and systems for using an application server (AS) to trigger home subscriber server (HSS)-based proxy call session control function (P-CSCF) restoration for a user equipment (UE) in order to restore service to the UE via an in-service P-CSCF node. For example, an AS is configured to receive, from a serving CSCF (S-CSCF) node, an indication that a P-CSCF node assigned to a UE is unavailable, and, in response, the AS is configured to send, to a HSS, a request to initiate P-CSCF restoration for the UE. In turn, the HSS or a Unified Data Management (UDM) node is configured to send, to a control node, an indication to perform the P-CSCF restoration for the UE. The disclosed AS-triggered, HSS-based P-CSCF restoration procedure restores service to the UE.