A security gateway (SEG) is a high-performance IPsec tunneling gateway that connects the service provider’s Evolved Packet Core (EPC) to base stations (eNodeBs and gNodeBs) on the S1/NG interface and handles connections between base stations on the X2/Xn interface.
Security gateway IPsec functionality can protect traffic as it traverses mobile backhaul by establishing an encrypted, protected connection between the service provider’s base station and EPC network. The security gateway simplifies the provisioning burden for S1-MME and S1-U (NG-C and NG-U for 5G) traffic by being a central point of IPsec concentration. (See 5G Security Strategy Considerations to learn why a security gateway is important in 5G network deployments.)