Cisco Cisco ASR 5000
Direct Tunnelling for the S4-SGSN
▀ How It Works
▄ SGSN Administration Guide, StarOS Release 18
How It Works
Establishment of Direct Tunnel
The S4-SGSN uses the S12 interface for DT.
Direct Tunnel Activation for Primary PDP Context
For the PDP Context Activation procedure this solution uses new information elements (IEs) for the GPRS Tunnelling
Protocol v2 (GTPv2) as defined in TS 29.274. SGSN provides the user plane addresses for RNC and S-GW as S12U
FTEIDs as illustrated in the figure below.
Protocol v2 (GTPv2) as defined in TS 29.274. SGSN provides the user plane addresses for RNC and S-GW as S12U
FTEIDs as illustrated in the figure below.
The sequence for establishing a direct tunnel between the RNC and S-GW during PDP activation is as follows:
SGSN sends a Create Session Request to the S-GW with the indication flag DTF (direct tunnel flag) bit set
In its Create Session Response, the S-GW sends the SGSN an S12U FTEID (Fully Qualified Tunnel Endpoint
Identifier).
The SGSN forwards the S-GW S12U to the RNC during the RAB Assignment Request.
In its RAB Assignment Response, the RNC sends the SGSN its transport address and Tunnel Endpoint ID
(TEID).
The SGSN forward the RNC S12 U FTEID o the S-GW via a Modify Bearer Request.
Figure 26. Primary PDP Activation with Direct Tunnel