- As Mobile Network is evolving day by day with huge business insights and budgets, we always need to fully utilize the usage of legacy as well as newer generations.
- So we MUST have the concept of Interconnectivity.
- We have some mandatory Interfaces that are used for mobility between different RATs.
SGs: Mandatory for CSFB, and connects the LTE MME with Legacy MSC. Also used for an SMS solution called SMSoS.
S3: It connects MME with SGSN to provide a signaling exchange between different 3GPP Access Technologies ( LTE & Legacy )
S4: It Connects SGW with SGSN and used for User Plane exchange between different 3GPP Access Technologies ( LTE & Legacy ). It is Also used as an anchoring interface for Inter - RAT Handover
S12: It is an MNO optional configuration, connects SGW with RNC and mainly used for Direct Tunneling.
