Reference Link: http://support.huawei.com/hdx/hdx.do?docid=SE0000750074&lang=en  -------->solutions

Definition:

The increasing development of 3G services and technology applications, such as high speed packet access (HSPA), requires improvement on the user-plane processing capability in the packet switched (PS) domain of the Universal Mobile Telecommunications System (UMTS) core network. Previously, the GPRS Tunneling Protocol-User plane (GTP-U) tunnels were set up between the radio network controller (RNC) and serving GPRS support node (SGSN) and between the SGSN and gateway GPRS support node (GGSN), which required two tunnels. Consequently, the user-plane processing capability needed to be improved in all of the RNC, SGSN, and GGSN. This type of improvement requires more investments and increases operating expenses.

Under such circumstances, the 3rd Generation Partnership Project (3GPP) introduced the direct tunnel solution that could reduce investments and operating expenses, and facilitate future network expansion. In the direct tunnel solution, one GPRS Tunneling Protocol (GTP) tunnel between the RNC and GGSN is used instead of the two user-plane tunnels between the RNC and SGSN, and the SGSN and GGSN. The SGSN does not need to forward user-plane data, which saves user-plane resources, reduces investment needs and operating expenses, and optimizes the user-plane performance of the PS domain of the UMTS core network.

Benefits:

Table 1 Benefits of this feature

Impact on the System:

• For the control plane, the SGSN needs to send Update PDP Context messages to the GGSN during PDP context activation procedure, PDP context preservation procedure, and service request procedure, which increases the signaling processing load of the SGSN and the GGSN.
• For the user plane, the user-plane data of the GGSN is directly sent to the RNC. This reduces the processing load of the SGSN, saves user-plane resources of the SGSN, and improves user experience by shortening data transmission delay.

Networking Architecture:

After the PS domain of theUMTS core network employs the direct tunnel solution, the original network structure changes. That is, the GTP-U tunnel is set up directly between the RNC and the GGSN; in addition, the indirect-tunnel mode is also supported. Figure 1 shows the networking architecture for the Direct Tunnel feature.

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Considering the main benefits are the CAPEX and capacity savings, there are some challenge

With Direct Tunnel, data packets between the IP-based internet and the WCDMA network would be tunneled directly from the RNCs to the GGSNs. The SGSN would only establish the connection and handle location and charging-related tasks – and would no longer handle data traffic between the RNCs and GGSNs.