Both HSG (HotSpot Gateway) and HSA (HotSpot Access) can be used for providing hotspot access (Captive Portal, AAA, user control etc).

HSG supports any brands or models of  wireless infrastructure for connecting to user devices. As long as the user traffic passes through mbox, it can enforce the required access control. HSG is primarily used for large organizations, as a gateway for central access control and user management. It is designed for two profiles of environmentswhere there’re existing wireless or wired infrastructures. Use HSG as a gateway to gain additional access control and offer new services on top of existing Wi-Fi infrastructure

• • Greenfield implementation for large networks, such as campus, shopping center and malls, hotels/hostels/dormitories, hospitals, cinemas, and large enterprise offices, etc. Use HSG together with any other Wi-Fi solution to offer guest Wi-Fi services.

HSA can act as a "mini" HSG for smaller hotspot network, but it has no built-in RADIUS and Captive Portal, and is designed to work with central HSG or mfusion (where RADIUS and CP are hosted) to provide hotspot solutions for smaller venues, eg. F&B, retails outlets, motels etc. 

Please refer to sections below for different design scenarios.