Cisco Cisco ASR 5000
ISR with Circuit Switched Fallback
▀ ISR CSFB Procedures
▄ SGSN Administration Guide, StarOS Release 18
ISR CSFB Procedures
CS Paging Procedure
The call flow below depicts a CS Paging example:
Figure 49. CS Paging
Table 22. Steps in a CS Paging Procedure
Step Description
1.
A Mobile Terminating call arrives at MSC/VLR (via the G-MSC) for a UE which is camped on E-UTRAN.
2.
If the ISR is active and the SGs interface is active between MSC and MME, then the MSC/VLR sends a Page Request
(SGsAP-PAGING-REQUEST) to the MME.
(SGsAP-PAGING-REQUEST) to the MME.
3.
As ISR is active and the UE is in ECM_IDLE state, the MME forwards the CS paging message received from the
MSC/VLR to the associated SGSN. The MME receives the SGSN information in the regular ISR activation process. The
MME builds a "CS Paging Indication" message, which is a GTPv2 message, from the SGsAP-PAGING_REQUEST to the
correct SGSN.
MSC/VLR to the associated SGSN. The MME receives the SGSN information in the regular ISR activation process. The
MME builds a "CS Paging Indication" message, which is a GTPv2 message, from the SGsAP-PAGING_REQUEST to the
correct SGSN.
4.
The SGSN receives the CS Paging Indication message from the MME, and sends paging messages to RNS/BSSs.
5.
The RNS/BSS forwards the CS Paging Indication message to the UE.
6.
The CS fallback or Cell re-selection process progresses.
7.
Once the process is complete, the UE sends a CS Paging response to the RNS/BSS.
8.
The RNS/BSS forwards the CS Paging Response to the MSC/VLR.
For detailed information on CS paging procedure refer to 3GPP TS 23.060.