I-RAT Network Architecture

I-RAT Network Architecture

S3 & S4 Interfaces:

Ø  S3/S4 are Interfaces between EPC and 2G/3G packet switched core network domain.

Ø  They would allow inter-system changes between SAE and 2G/3G

Ø  The S3 is a pure signaling interface used to coordinate the inter-system change between MME  and SGSN

Ø  The S4 is the user plane interface and it is located between SGSN and serving SAE GW.

Ø  This would allow to either forward packet data from EUTRAN via serving SAE GW to SGSN (and then to GGSN) or from 2G/3G RAN to SGSN to serving SAE GW to PDN GW.

UTRAN Direct Tunnel:

Ø  S12 is the interface between EPC and 3G Radio access network

Ø  It would allow inter-system changes between SAE and 3G

Ø  The S12 is the user plane interface used for tunneling user data directly between the Serving SAE SW and the UTRAN

Ø  This would allow to forward packet data from 3G RAN to serving  SAE GW to PDN GW.

Ø  It is based on the Gn interface between the SGSN and the GGSN and so uses the GTP-U protocol.