Serving GPRS Support Node (SGSN) Overview
▀ Features and Functionality - Enhanced and Licensed
▄ Cisco ASR 5000 Series Product Overview
Figure 167. GTP-U with Direct Tunnel
In effect, a direct tunnel reduces data plane latency as the tunnel functionality acts to remove the SGSN from the data
plane and limit the SGSN to the control plane for processing. 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 establishes a direct tunnel at PDP context activation using an Update PDP Context Request
towards 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 system‘s platform capabilities ensure control plane
capacity will not be a limiting factor with direct tunnel deployment.
For more information on Direct Tunnel configuration, refer to the SGSN Direct Tunnel Configuration chapter in the
System Enhanced Feature Configuration Guide.
Lawful Intercept
The SGSN supports lawful interception (LI) of subscriber session information to provide telecommunication service
providers (TSPs) with a mechanism to assist law enforcement agencies (LEAs) in the monitoring of suspicious
individuals (referred to as targets) for potential criminal activity.
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