3GPP 24.501 v20.0.0 — the document's own text
8.3.7.15 Service-level-AA container
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
This IE shall be included in the message when the UE needs to modify an established PDU session for C2 communication.