3GDT – 3G Direct Tunnel
(3GDT) allows the setup of a GTP-U tunnel for transporting the payload traffic directly between the RNC and GGSN, thus bypassing the SGSN. This reduces the payload traffic that needs to transverse the SGSN.
3GDT reduces the payload traffic through the SGSN by transporting the user traffic outside the SGSN, between the Gateway GPRS Support Node (GGSN) and Radio Network Controller (RNC) directly. According to 3GPP, 3GDT requires support in both the GGSN and RNC, and requires also that optionally additional entries are configured in the Domain Name System (DNS) and Home Location Register (HLR).
The GTP-U tunnel for transporting traffic between the GGSN and RNC directly is referred to as the “direct tunnel”. The configuration where 3GDT is not activated and the SGSN is not bypassed is referred to as the “two-tunnel solution“.
3GDT can be configured in the following nodes:
The 3GDT feature can be configured based on one of the following modes:
- Subscriber per APN(HLR configuration)
- GGSN per APN (DNS configuration)
- Per APN (SGSN configuration)
- Per TAC (SGSN configuration)
- Per GGSN (SGSN configuration)
If the SGSN uses 3GDT, a direct tunnel between the GGSN and RNC replaces the two-tunnel solution in the user plane and the SGSN then continuously updates both the GGSN and RNC with information regarding the user-plane Tunnel Endpoint Identifier (TEID) values and Internet Protocol (IP) addresses.
