What is the reason for only part of the 3G data traffic to be going through the 3G Direct Tunnel and another part is going through the SGSN. There are counters for traffic in IuPS interface which still show there is data traffic in the SGSN. The greater part of the traffic is going through the Direct Tunnel, but not all. The Iu user plane traffic should go through the Direct tunnel and the Iu control plane traffic should go to the SGSN. And counters still show user pane traffic going through the SGSN. There must be a reason for this.

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3 Answers 3


Yes, there is a reason to it.

Be advised that even if the 3GDT is set up between RNC and GGSN, the "2G non home public" users , ie "2G roamer users" only use IuPS on your picture, and don't use 3GDT.

We both know that 2G users can access 3G Core network depending on the policy of authorization mode based on IMSI or based on algorithm mode in SGSN.

The SGSN does not enable 3GDT for 2G Data user: for 2G data subscriber, the SGSN sends a RAB message request information containing user-plane IP address and TEID of the SGSN, not GGSN to the RNC.

To do:

Please export the number of 2G Data Subscriber in your network and export also the number of 2G PDP Context, there are chances they will correspond.


SGSN does have data traffic on IuPS interface with 3GDT implemented . This payload is 3G inroamer subscriber , as inroamer subscriber would go to thier home ggsn and not visited plmn ggsn (if vplmn not allowed) .


I think 2G Data user(Home subscriber) also can use 3GDT, For BSC-------lu-u------GGSN (for 3GDT) BSC--------Gb----SGSN-----Gn/Gp-----GGSN (For Non-3GDT)

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