Bootstrapping Server function (BSF) is part of Generic Authentication Scheme (GBA Generic Bootstrapping Architecture) or Generic Authentication Architecture (GAA) which consists of following elements.
- User Equipment (UE)
- Application Server (NAF: Network Application Function), e. g. for mobile TV; provides the service
- BSF (Bootstrapping Server Function); arranges security relation between UE and NAF
- mobile network operator's Home Subscriber Server (HSS) which hosts user profiles
Now coming to the LTE network, BSF queries the Subscriber Locator Function (SLF) over Zh interface (Diameter based) to get the name of the HSS containing the required subscriber specific data.
Above is the message flow between various entities, BSF mutually authenticate UE and server that host a service using the service key i.e. B-TID. BSF generates the session key (B-TID) and pass it to UE, after receiving B-TID UE access services using B-TID from NAF.