In recent years, the mobile networks have evolved from a circuit switched approach to a complete packet switched one. The LTE-EPS network (Long Term Evolution - Evolved Packet Core) offers high bandwidth, low latency and improved spectrum efficiency. It provides IP connectivity but does not support valuable legacy services such as the SMS (Short Message Service) in Release 8 to 10. 3GPP is currently specifying two architectures for SMS transmission over LTE in Release 11. The objective of this report is to describe and analyze these architectures with a particular focus on the new gateway called IP-SM-GW (IP Short Message Gateway). Two complementary scenarios are proposed by 3GPP , depending on the type of LTE device used. When an SMS-capable LTE device communicates to a GSM device, the gateway realizes transport level interworking. However, if the LTE user is unable to create or read SMSs, the IP-SM-GW performs service level interworking. The implementation of an IP-SM-GW is transparent to the end user, and does not imply any changes in the 2G/3G architecture. This solution is necessary for an operator since it offers his subscribers a higher level of trust and a better acceptance of the implementation of LTE.
