Cisco Cisco ASR 5000
Direct Tunnelling for the S4-SGSN
▀ How It Works
▄ SGSN Administration Guide, StarOS Release 18
Figure 31. Downlink Data Notification with Direct Tunnel
Downlink Data Notification with Direct Tunnel when UE in Idle State
When an Iu is released the UE goes IDLE. The SGSN informs the S-GW to release the RNC side TEIDs by sending a
Release Access Bearer Request. After this point if the S-GW receives any downlink GTPU data from the P-GW, it
knows neither the RNC TEID nor SGSN user plane TEID to which to forward the data.
Release Access Bearer Request. After this point if the S-GW receives any downlink GTPU data from the P-GW, it
knows neither the RNC TEID nor SGSN user plane TEID to which to forward the data.
If the S-GW receives any downlink GTPU data after receiving the Release Access Bearer Request, it knows neither the
RNC TEID nor SGSN user plane TEID to which to forward the data. So it signals the SGSN to establish the RABs. This
signaling message is a Downlink Data Notification from the S-GW. If a Downlink Data Notification is received from S-
GW when the UE is idle, the SGSN pages the UE before establishing the RABs. The SGSN sends a Modify Bearer
Request to the S-GW with the RNC S12U FTEID.
RNC TEID nor SGSN user plane TEID to which to forward the data. So it signals the SGSN to establish the RABs. This
signaling message is a Downlink Data Notification from the S-GW. If a Downlink Data Notification is received from S-
GW when the UE is idle, the SGSN pages the UE before establishing the RABs. The SGSN sends a Modify Bearer
Request to the S-GW with the RNC S12U FTEID.
Figure 32. Downlink Data Notification when UE in Idle State