Request Routing with Chained DSR Applications

Application Chaining is a method for invoking multiple DSR Applications in sequence on the same DSR.

Figure 1 shows an example of Request processing for two DSR Applications executing in sequence. The Application Route Table in this example is executed three times:

When the Request enters the system at (1)
When DSR Application 1 sends the Request back to the Diameter Routing Function at (3)
when DSR Application 2 sends the Request back to the Diameter Routing Function at (5)
At (5) there is no matching Application Routing Rule for the Request, the Request is routed to Peer Route Table processing.

Request Processing with Multiple DSR Applications

Application Route Table (ART)
Application Route Tables are used for routing Request messages to DSR Applications. An ART contains a prioritized list of user-configurable Application Routing Rules. Each Application Routing Rule associates Request message content with a DSR Application.

An ART is searched when a Request message is received from a Peer Node or a DSR Application. Searching an ART when a Request message is received from a DSR Application allows the operator to route the ingress Diameter transaction to multiple DSR Applications in sequence. The operator can create multiple ARTs to assign an ART to a Request message based upon a set of user-defined criteria.
Application Routing Rules
An Application Route Table (ART) consists of a set of prioritized Application Routing Rules that the Diameter Routing Function searches with the content of a Request message, to determine whether the message should be forwarded to a DSR Application for processing.

One ART is searched each time a Request message is received from a Peer Node or a DSR Application. This method allows forwarding a Diameter transaction to one or more DSR Applications for processing.

However, the Diameter Routing Function does not allow a DSR Application to process a Diameter transaction more than once. (The Diameter Routing Function internally keeps track of which DSR Applications have already processed the message.) When the Diameter Routing Function is searching an ART and encounters an Application Routing Rule that is associated with a DSR Application that has already processed the transaction, that Application Routing Rule will be bypassed.

The system always contains a Default ART that cannot be removed using the configuration GUI. The user can create additional ARTs and then define, through configuration, which ART will be searched based on ART precedence selection rules.

Each time that a Request message is received from a Peer Node or DSR Application, the Diameter Routing Function selects an ART to search based on the following ART precedence selection rules (highest to lowest priority):

The ART provided by the DSR Application, if it exists (applies only when the Request message was received from a DSR Application)
The ART assigned to the ingress Peer Node from which the Request message was received, if it exists
The ART assigned to the Diameter Application ID in the Request message header, if it exists
The Default ART

The order of DSR Applications which can process an ingress Request message is determined by operator configuration of one or more Application Route Tables.

Each time the Diameter Routing Function receives a Request message from a Peer Node or DSR Application, it searches the Application Route Tables to determine where to forward the message.
The highest priority Application Routing Rule matched defines where to forward the message.
If no Application Routing Rule match is found, the Diameter Routing Function begins Relay Agent routing to an upstream Peer Node.

When FABR and the Diameter-MAP Interworking (DM-IWF) applications run in the same DA-MP, the same Diameter Request message can be processed by both applications.

For a Diameter-to-MAP Request message received from a Diameter Peer that needs to be processed by FABR followed by DM-IWF, two Application Routing Rules are needed; one for routing the message first to FABR and the second one to route the message to DM-IWF after FABR processing is completed

After the Request is received from the Peer, the Diameter Routing Function searches the Application Routing Rules for the highest priority matching rule. This rule contains the FABR application name, and will result in the Request being routed to FABR.
FABR processes the message and returns it to the Diameter Routing Function.
The Diameter Routing Function searches the Application Routing Rules for the highest priority matching rule (excluding all rules that would result in routing of the Request to FABR again).This rule contains the DM-IWF application name, and will result in the Request being routed to DM-IWF.
DM-IWF processes the message and sends it to an MD-IWF application (SS7-MP).

For a MAP-to-Diameter Request message received by DM-IWF from an MD-IWF application (SS7-MP) that needs to be processed by FABR after DM-IWF processing, a single Application Routing Rule is needed for routing the message to FABR after DM-IWF processing is completed.

DM-IWF processes the message and sends it to the Diameter Routing Function.
The Diameter Routing Function searches the Application Routing Rule for the highest priority matching rule (excluding all rules that would cause routing of the Request to DM-IWF again). This rule contains the FABR application name, and will result in the Request being routed to FABR for processing.
FABR returns the message to the Diameter Routing Function to complete the routing process.