This section explains the components of the Sentinel Authentication Gateway and how they implement 3GPP GAA.

The 3GPP Generic Authentication Architecture provides a standard way for User Equipment (UEs) to securely access Network Application Functions (NAFs) or application servers.

Note This section assumes some familiarity with GAA roles. See Introduction to 3GPP GAA for background information.

Sentinel Authentication Gateway's 3GPP GAA implementation

Sentinel Authentication Gateway implements the BSF and NAF roles in 3GPP GAA. The UE talks to these components over the Ub and Ua interfaces, as shown in the network model below, reproduced from 3GPP TS 33.220:

GAA network model
Figure 1. Simple GAA network model (3GPP TS 33.220 §5.1)

In Sentinel Authentication Gateway, the BSF Server component implements the BSF role, and is implemented as a SLEE service deployed on OpenCloud Rhino. The UE communicates with the BSF using the Ub (bootstrapping) interface over HTTP on port 80.

The NAF role is implemented by the NAF Authentication Filter, which is deployed as a servlet filter layer in front of the Sentinel VoLTE XCAP web application, and a Proxy Servlet which is able to forward requests on to other external web applications. The UE communicates with Sentinel VoLTE XCAP or the Proxy Servlet using the Ut interface over HTTP or HTTPS. The NAF Authentication Filter intercepts these requests to authenticate the user (Ua interface), before passing them to the XCAP server or other web application.

Both components share state using a Cassandra database. This is functionally equivalent to the Zn interface in the model above. Sharing state in a database allows the BSF and NAF nodes to be stateless, and to easily scale out horizontally.

The diagram below shows the relationship between Sentinel Authentication Gateway components, the UE, the Sh Cache Microservice and the HSS.

Sentinel Authentication Gateway Architecture
Figure 2. Sentinel Authentication Gateway architecture

The following sections explain the architecture of the BSF Server and NAF Authentication Filter by following a typical authentication and bootstrapping process as a client attempts to access a NAF resource.

Compliance Notes

Zn interface

Sentinel Authentication Gateway currently does not support third-party BSFs or NAFs, because it uses a database to implement NAF to BSF communication instead of the Diameter or HTTP-based Zn interface (3GPP TS 29.109). A future Sentinel Authentication Gateway release may remove this limitation.

Authentication schemes

The BSF Server supports the Digest-AKAv1-MD5 and GBA_Digest authentication schemes.

The NAF Authentication Filter supports the MD5 and SHA256 digest algorithms.

Additional variants may be supported in future Sentinel Authentication Gateway releases.

Bootstrapping procedures

The BSF Server currently supports the GBA (or GBA_ME), and GBA_Digest bootstrapping procedures. A future release will support GBA_U, UICC enhancements to Generic Bootstrapping Architecture (3GPP TS 33.220 §5).

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