Hello,
The GSM network architecture consists of different elements including Base Station Subsystem BSS that includes the GBTS and BSC, core network (CN), and terminal device. The interfaces between particular elements of the system are defined and they determine rules for cooperation between devices.

LTE has a flat architecture which stems from the system architecture of the previous generation, namely from UMTS. The Evolved Packet Core (EPC) LTE architecture has the following core elements: eNB (E-UTRAN Node B), SGSN, HSS, MME (Mobile Management Entity), and UE.

Detail
https://forum.huawei.com/enterprise/en/difference-between-lte-and-gsm/thread/551989-100305
Thanks