Implicit Routing Rules
Certain network element functions require routing rules to be configured along with the function. These routing rules are called Implicit routing rules. For instance, when you assign the HSS function to a Diameter Remote Network Element, you need to specify which subscribers are served by the HSS. This is done by assigning the HSS function and configuring the implicit routing in the function configuration.
Implicit routing is usually based on subscriber identity or realm. In 3GPP WLAN networks, the subscriber identity is the IMSI (International Mobile Subscriber Identity) of the mobile device (WLAN UE).
The functions that require you to configure implicit routing include the Downstream server function (supported in both RADIUS and Diameter) and the HSS, CDF and WAG (Diameter) functions.
For a complete discussion of implicit routing rules and how to configure them, see Implicit Routing Rules.