Mobile Packet Core

Gb Interface

• Gb interface is the interface between the BSC and the SGSN, and it uses the BSSGP protocol.
• BSSGP refers to 'BSS GPRS Protocol', and it provides routing,  and QoS related information between the BSC and the SGSN.

Iu-PS interface

The Iu-PS interface is the interface between the RNC and the SGSN. This interface uses different protocols in control plane and user plane.

Iu-PS interface in control plane

• The IuPS interface in control plane uses RANAP protocol.
• RANAP protocol handles signalling messages like 'RAB establishment' between the RNC and the SGSN.

Iu-PS interface in user plane

• The Iu-PS interface in user plane uses GTP-U protocol.
• The protocol stack of the IuPS interface in user plan, is the same as the Gn interface.

• This is because when using Direct Tunnel, the RNC will communicate directly with the GGSN in the user plane, instead of the SGSN. Therefore, the protocol stack between them should be the same.