Section: 7.4.8 UE Activity Notification
Content: A UE Activity Notification message shall be sent on the S3 interface by the SGSN to the associated MME as part of an SGs Non-EPS alert procedure (see 3GPP TS 29.118[ Mobility Management Entity (MME) - Visitor Location Register (VLR) SGs interface specification ]  [22]) when ISR is activated, except under the conditions specified in 3GPP TS 23.272[ Circuit Switched (CS) fallback in Evolved Packet System (EPS); Stage 2 ]  [21], to indicate that activity from a UE has been detected. Table 7.4.8-1 specifies the presence requirements and the conditions of the IEs in the message. Table 7.4.8-1: Information Element in UE Activity Notification