Full Address Based Resolution overview

Full Address Based Resolution (FABR) is a routing application that enables network operators to resolve the designated Diameter server (IMS HSS, LTE HSS, MTC HSS, PCRF, OCS, OFCS, AAA) addresses based on Diameter Application ID, Command Code, Routing Entity Type, and Routing Entity Addresses, and then routes the Diameter Request to the resolved destination.

The FABR application validates the ingress Diameter Request message, retrieves the Application ID and Command Code from it, and determines the desired Routing Entity Type to decode 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 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 replaces the Destination-Host and/or Destination-Realm AVP in the ingress Request message with the corresponding values of the resolved Destination, and forwards the message to the Diameter Relay Agent for egress routing into the network.

A Routing Entity can be any of the following:

• International Mobile Subscriber Identity (IMSI)
• Mobile Subscriber Integrated Services Digital Network (Number) (MSISDN)
• IP Multimedia Private Identity (IMPI)
• IP Multimedia Public Identity (IMPU)
• External Identifier

FABR Functions

FABR provides the following functions:

• Routing based on IMSI/MSISDN Prefix Lookup performs prefix-based lookups after completion of the full address lookup. The prefix and range based lookup are only 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.

  Populates the Destination-Host AVP and/or the Destination-Realm AVP based on the resolved destination if a match is found in the prefix database.

  Performs the No Address Match Found routing exception handling procedure if there is not a match in the prefix database.

  The IMSI/MSISDN Prefix and Range lookup can be enabled or disabled on system wide.

• DP Query Bundling enhances the FABR-to-DP interface by supporting the bundling of multiple queries into a single bundled query stack event when enabled.

  When the DP receives a bundled query, the corresponding bundled response have responses to all the queries that constitute the bundled query.

• Reserved MCC Ranges are reserved for future Mobile Country Code (MCC) ranges and 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 are NOT used for further address resolution. FABR continues decoding the digits using other AVP instances or next Priority AVP (if provisioned), or next Routing Entity (if provisioned).
• Identifying IMSI, MSISDN, and External Identifier 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 plus sign before the digits, the Routing Entity Type is IMPU, and decoded digits fall within MSISDN and IMSI overlap range. Configured MCC+MNC combinations can be compared to the first 5 or 6 digits of the User Identity. The User Identity is considered as an IMSI and used for IMSI lookup if a match occurs. The User Identity considered as a MSISDN and used for MSISDN lookup if a match does not occur.

  Identifying IMSIs and MSISDNs provides more information about identifying IMSIs and MSISDNs using digit string lengths and MCC+MNC combinations.

• Application Chaining allows FABR and the DM-IWF applications to process the same Diameter Request message by configuring application routing rules.