Direct Tunnel for 4G Networks - Feature Description
The amount of user plane data will increase significantly during the next few years because of High Speed Packet Access (HSPA) and IP Multimedia Subsystem technologies. Direct tunneling of user plane data between the RNC and the S-GW can be employed to scale UMTS system architecture to support higher traffic rates.
Direct Tunnel (DT) offers a solution that optimizes core architecture without impact to UEs and can be deployed independently of the LTE/SAE architecture.
Direct tunnel is a licensed Cisco feature. A separate feature license is required for configuration. Contact your Cisco account representative for detailed information on specific licensing requirements. For information on installing and verifying licenses, refer to the Managing License Keys section of the Software Management Operations chapter in the System Administration Guide.
Establishment of a direct tunnel is controlled by the SGSN; for 4G networks this requires an S4 license-enabled SGSN setup and configured as an S4-SGSN.
Once a direct tunnel is established, the S4-SGSN/S-GW continues to handle the control plane (RANAP/GTP-C) signaling and retains the responsibility of making the decision to establish direct tunnel at PDP context activation.
A direct tunnel improves the user experience (for example, expedites web page delivery, reduces round trip delay for conversational services) by eliminating switching latency from the user plane. An additional advantage, direct tunnel functionality implements optimization to improve the usage of user plane resources (and hardware) by removing the requirement from the S4-SGSN/S-GW to handle the user plane processing.
A direct tunnel is achieved upon PDP context activation when the S4-SGSN establishes a user plane tunnel (GTP-U tunnel) directly between the RNC and the S-GW over an S12 interface, using a Create Bearer Response or Modify Bearer Request towards the S-GW.
A major consequence of deploying a direct tunnel is that it produces a significant increase in control plane load on both the SGSN/S-GW and GGSN/P-GW components of the packet core. Hence, deployment requires highly scalable GGSNs/P-GWs since the volume and frequency of Update PDP Context messages to the GGSN/P-GW will increase substantially. The SGSN/S-GW platform capabilities ensure control plane capacity will not be a limiting factor with direct tunnel deployment.
- Primary PDP activation
- Secondary PDP activation
- Service Request Procedure
- Intra SGSN Routing Area Update without S-GW change
- Intra SGSN Routing Area Update with S-GW change
- Intra SGSN SRNS relocation without S-GW change
- Intra SGSN SRNS relocation with S-GW change
- New SGSN SRNS relocation with S-GW change
- New SGSN SRNS relocation without S-GW relocation
- E-UTRAN-to-UTRAN Iu mode IRAT handover with application of S12U FTEID for Indirect Data Forwarding Tunnels as well
- UTRAN-to-E-UTRAN Iu mode IRAT handover with application of S12U FTEID for Indirect Data Forwarding Tunnels as well
- Network Initiated PDP Activation
- RAB Release
- Iu Release
- Error Indication from RNC
- Downlink Data Notification from S-GW
- Downlink Data Error Indication from S-GW
- MS Initiated PDP Modification
- P-GW Initiated PDP Modification while the UE is IDLE
- HLR/HSS Initiated PDP Modification
- Session Recovery with Direct Tunnel
The above scenarios exhibit procedural differences in S4-SGSN when a direct tunnel is established.