Full Address Based Resolution (FABR) is a DSR enhanced routing application that enables network operators to resolve the designated Diameter server (IMS HSS, LTE HSS, PCRF, OCS, OFCS, and AAA) addresses based on Diameter Application ID, Command Code, Routing Entity Type, and Routing Entity Addresses, and route the Diameter Request to the resolved destination.
The FABR DSR Application validates the ingress Diameter Request message, retrieves the Application ID and Command Code from it, and determines the desired Routing Entity Type to be decoded from the message, based on the configuration. The FABR application extracts the Routing Entity Address from user-configured Attribute-Value Pairs (AVPs) in the ingress message and sends the Routing Entity Address, if extracted successfully, to an off-board DP that is running the Subscriber Database Server (SDS) for destination address resolution.
The resolved Destination address can be any combination of a Realm and Fully Qualified Domain Name (FQDN); Realm-only, FQDN-only, or Realm and FQDN.
FABR will replace the Destination-Host and/or Destination-Realm AVP in the ingress Request message with the corresponding values of the resolved Destination, and forward the message to the Diameter Relay Agent for egress routing into the network.
FABR provides the following functions:
Routing Based on IMSI/MSISDN Prefix Lookup
If configured, FABR will perform prefix based lookups after the full address lookup is performed. The prefix and range based lookup will only be performed if the full address lookup does not find a match, and can be enabled by the operator for a combination of Application-Id, Command-Code and Routing Entity Type.
If a match is found in the prefix database, that FABR application will populate the Destination-Host AVP and/or the Destination-Realm AVP based on the resolved destination
If a match is not found in the prefix database, then FABR will perform the "No Address Match Found" routing exception handling procedure.
The IMSI/MSISDN Prefix and Range lookup can be enabled or disabled on a system wide basis.
DP Query Bundling
FABR DP Query Bundling enhances the FABR-to-DP interface by supporting the bundling of multiple queries into a single "bundled query" stack event if bundling is enabled.
When "bundled query" is received by the DP, the corresponding "bundled response" will have responses to all the queries that constitute the "bundled query".
Reserved MCC Ranges
Mobile Country Code (MCC) ranges that are reserved for future use are defined in a system-wide MCC Ranges table. If the MCC digits portion of decoded IMSI digits fall within one of the ranges designated in the MCC Ranges table, the IMSI digits will NOT be used for further Address Resolution. FABR will continue decoding the digits using other AVP instances, or next PriorityAVP (if provisioned), or next Routing Entity (if provisioned).
Identifying IMSIs and MSISDNs
Address resolution applications like Full Address Based Resolution (FABR) and Range Based Address Resolution (RBAR) need to categorize User Identities (digit strings) decoded from the Diameter Request AVPs as either MSISDN or IMSI, to allow looking up the User Identity in the appropriate lookup table.
If there is no ""+" sign before the digits, the Routing Entity Type is IMPU, and decoded digits falls within MSISDN and IMSI overlap range, configured MCC+MNC combinations can be compared to the first 5 or 6 digits of the User Identity. If a match occurs, the User Identity is considered as an IMSI and used for IMSI lookup. If a match does not occur, the User Identity is considered as a MSISDN and used for MSISDN lookup.
See Identifying IMSIs and MSISDNs for more information about identifying IMSIs and MSISDNs using digit string lengths and MCC+MNC combinations.
Application Chaining
Application Routing Rules can be configured so that FABR and the DM-IWF applications can both process the same Diameter Request message. See Request Routing with Chained DSR Applications.