Cisco Cisco ASR 5000
Direct Tunnelling for the S4-SGSN
How It Works ▀
SGSN Administration Guide, StarOS Release 18 ▄
Service Request with Direct Tunnel
When a UE is Idle and wants to establish a data or signaling connection, it sends a Service Request for data.
Alternatively a UE can also send a Service Request to the SGSN when it is paged by the SGSN.
Alternatively a UE can also send a Service Request to the SGSN when it is paged by the SGSN.
Upon receiving a Service Request for data, the SGSN establishes RABs and sends a Modify Bearer Request to the S-
GW with the 12U FTEID received from the RNC.
GW with the 12U FTEID received from the RNC.
Figure 30. Service Request Procedure with Direct Tunnel
Downlink Data Notification with Direct Tunnel when UE in Connected State
When RABs are released (but UE retains an Iu connection with the SGSN), the SGSN notifies the S-GW to release the
RNC side TEIDs via a Release Access Bearer Request.
RNC side TEIDs via a Release Access Bearer Request.
If the S-GW receives any downlink GTPU data from the P-GW 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 message from the S-GW.
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 message from the S-GW.
If the Downlink Data Notification is received from the S-GW, all of the missing RABs are established and a Modify
Bearer Request is sent to the S-GW with the RNC S12U FTEID
Bearer Request is sent to the S-GW with the RNC S12U FTEID