Cisco Cisco Packet Data Interworking Function (PDIF) Guía Para Resolver Problemas
Direct Tunnel
▀ Direct Tunnel Feature Overview
▄ Cisco ASR 5000 Series Enhanced Feature Configuration Guide
OL-22983-01
Direct Tunnel Feature Overview
The direct tunnel architecture allows the SGSN to establish a direct user plane tunnel between the radio access network
(RAN) and the GGSN. Once a direct tunnel is established the SGSN continues to handle the control plane signaling.
This improves the user experience (e.g., expedites web page delivery, reduces round trip delay for conversational
services). Additionally, direct tunnel functionality implements the standard SGSN optimization to improve the usage of
user plane resources (and hardware) by removing the requirement from the SGSN to handle the user plane processing.
(RAN) and the GGSN. Once a direct tunnel is established the SGSN continues to handle the control plane signaling.
This improves the user experience (e.g., expedites web page delivery, reduces round trip delay for conversational
services). Additionally, direct tunnel functionality implements the standard SGSN optimization to improve the usage of
user plane resources (and hardware) by removing the requirement from the SGSN to handle the user plane processing.
Typically, the SGSN sets up a direct tunnel at PDP context activation. The SGSN uses an Update PDP Context Request
towards the GGSN to establish a GTP user plane (GTP-U) tunnel directly between the RNC and the GGSN. This means
a significant increase in control plane load on both the SGSN and GGSN components of the packet core. Hence,
deployment requires highly scalable GGSNs since the volume and frequency of Update PDP Context messages to the
GGSN will increase substantially. The SGSN‘s platform capabilities ensure control plane capacity will not be a limiting
factor with direct tunnel deployment.
towards the GGSN to establish a GTP user plane (GTP-U) tunnel directly between the RNC and the GGSN. This means
a significant increase in control plane load on both the SGSN and GGSN components of the packet core. Hence,
deployment requires highly scalable GGSNs since the volume and frequency of Update PDP Context messages to the
GGSN will increase substantially. The SGSN‘s platform capabilities ensure control plane capacity will not be a limiting
factor with direct tunnel deployment.
Figure 5.
GTP-U Direct Tunnel
The following figure shows the logic used within the SGSN to determine if a direct tunnel can be used.