In LTE networks, there are three main SMS delivery solutions:
1) SMS over IP (SIP): Uses Session Initiation Protocol (SIP) to send SMS over IP networks. SMS is encapsulated in SIP and sent through the IMS core network, efficiently leveraging existing IMS infrastructure. IP-SM-GW is required to ensure interoperability between the IP-based LTE network and the legacy 2G/3G circuit-switched networks.
2) SMS over SGs (SGs-AP): Utilizes SGs interface for SMS delivery between LTE and legacy 2G/3G networks. Connects LTE's MME to 2G/3G MSC for SMS exchange using SGs-AP protocol.
3) SMS over SGd (Diameter): Uses SGd interface and Diameter protocol for SMS delivery in LTE without relying on legacy networks. Connects LTE's MME to legacy SMSC/SMGW, employing Diameter for signaling and SMS transport.
