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Routing Rule Evaluation and Rule Priorities

This section describes how the IMS AAA Server determines how to route requests and the routing rule priorities.

When a request is received, the IMS AAA Server identifies the request type and then evaluates the associated routing rules. First, the server evaluates any explicit routing rules defined for the request type. The order in which explicit routing rules are evaluated is user-defined. If no match is found, the server evaluates the implicit routing rules defined for the request type.

When a match is found, the IMS AAA Server processes the request by routing it to the specified destination. In some cases this may mean simply forwarding the request to the destination. In other cases, for example if the HSS is listed as the destination, the IMS AAA Server would consult the HSS for the subscriber credentials and then take the appropriate action.

If no routing rule match is found, the IMS AAA Server takes the appropriate action according to the respective RFC. For example, if the request is from a RADIUS based device, no response is provided, the request is simply discarded. If the request is Diameter based, a response with an appropriate result code is sent to the requestor.

Note that both implicit and explicit routing rules can use the realm portion of the NAI decoration (user name) for determining how to route requests. If the request does not contain an NAI, the Destination-Realm in the request is used; this applies to Diameter requests only. However, if the realm to which the request is to be routed is listed in the Local Network Element > Identification > Self Names field, the realm is ignored and the request is treated as if it contained no realm. If no realm is present in either the NAI or the Destination-Realm, the request is considered to be local.

NOTE: For convenience, the IMS AAA Server Administrator displays routing rules in the order in which they are evaluated.


Table 23 summarizes the priorities and routing rules for authentication requests. Authentication requests are applicable to the HSS function and the Downstream (server) function (both RADIUS and Diameter). These rules apply to RADIUS authentication/authorization requests and Diameter authentication requests.

Table 23: Summary of Routing Rule Priorities for Authentication Requests  
Priority
Rule
                  Functions
HSS
Downstream RADIUS or Diameter Server

1

Explicit

2

Implicit-IMSI Prefix

Not applicable.

3

Implicit-Realm

4

Implicit-Default IMSI

Not applicable.

5

Implicit-Default Realm


Table 24 summarizes the priorities and routing rules for authorization requests. Authorization requests are applicable only to the Downstream (server) function for Diameter.

Table 24: Summary of Routing Rule Priorities for Authorization Requests  
Priority
Rule
Downstream Diameter Server

1

Explicit

2

Implicit-Realm

3

Implicit-Default Realm


Table 25 summarizes the priorities and routing rules for accounting requests. Accounting requests are applicable only to the CDF function for Diameter.

Table 25: Summary of Routing Rule Priorities for Accounting Requests  
Priority
Rule
CDF

1

Explicit

2

Implicit-IMSI Prefix

3

Implicit-Realm

4

Implicit-Default IMSI

5

Implicit-Default Realm


Table 26 summarizes the priorities and routing rules for WAG requests (Diameter only).

Table 26: Summary of Routing Rule Priorities for WAG Requests  
Priority
Rule
WAG

1

Explicit

2

Implicit: Origin-Host

3

Implicit: Origin-Realm

4

Implicit: Default Origin-Host

5

Implicit: Default Origin-Realm



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