2.3 Request Message Validation

The RBAR application processes the diameter request message based on the configuration, to extract the user identity addresses.

When RBAR receives a diameter request message, the following validation is performed:

• Determine whether the Application ID in the message header is defined in the configuration.

  If a valid Application ID cannot be found, the message is not processed. An answer response with a Result code AVP for DIAMETER_APPLICATION_UNSUPPORTED is returned.

• If a valid (configured) Application ID is received in a diameter request message, validate whether the pair (Application ID, command code) received in the message is defined in the configuration.

  If the pair cannot be found in the configuration, the appropriate routing exception handling procedure is invoked.

• If the pair is configured, search for a valid routing entity address in the message based on the highest priority routing entity type (Primary routing entity type in address resolution configuration) assigned to the pair.
• Search for a valid routing entity address in the message based on a prioritized set of AVPs assigned to the triplet.

  If a valid routing entity address cannot be found in searching the configured routing entity types assigned to the pair, the routing exception handling procedure is invoked that is assigned to the Application ID and this routing entity type.

Routing Exception Handling

When an ingress RBAR request message cannot be resolved to a destination (no address matched, no valid digits decoded, or any other error returns), RBAR invokes a routing exception handling procedure based on user-defined configuration.

Routing exception handling procedures result in one for the following configured actions:

• Forward the message unchanged
• Forward the message using a user-defined default destination
• Send answer response with a user-defined result-code AVP value and error message AVP
• Send answer response with user-defined experimental-code AVP values and error message AVP
• Abandon request (discard the ingress diameter request message)

The routing exceptions support the following:

• Unknown command code
• Valid address not found
• Valid address was found and did not match a configured address or address range

Supported AVPs

RBAR supports the AVPs associated with a user identity type (IMSI, MSISDN, IMPI, IMPU) as defined in Table 2-1.

Table 2-1 RBAR Supported AVPs

For a User Identity Type (IMSI, MSISDN, IMPI, IMPU) AVPs	Vendor ID and AVP Code	AVP Type	AVP Reference
User-Name	Vendor-ID: none AVP code: 1	UTF8String	Section 8.14 of RFC 3588bis
Service-Information [Subscription-ID]	Vendor-ID: 10415 (3GPP) AVP code: 873	Grouped	Section 7.2.192 of 3GPP 32.299
Subscription-ID [Subscription-ID-Data]	Vendor-ID: none AVP code: 443	Grouped	Section 8.46 of RFC 4006
Subscription-ID-Data	Vendor-ID: none AVP code: 444	UTF8String	Section 8.48 of RFC 4006
Public-Identity	Vendor-ID: 10145 (3GPP) AVP code: 601	UTF8String	Section 6.3.2 of 3GPP 29.229
MSISDN	Vendor-ID: 10415 (3GPP) AVP code: 701	OctetString	Section 6.3.2 of 3GPP 29.329
User-Identity: [Public-Identity] [MSISDN]	Vendor-ID: 10415 (3GPP) AVP code: 700	Grouped	Section 6.3.1 of 3GPP 29.329
Public-Identity	Vendor-ID: 10145 (3GPP) AVP code: 601	UTF8String	Section 6.3.2 of 3GPP 29.229
MSISDN	Vendor-ID: 10415 (3GPP) AVP code: 701	OctetString	Section 6.3.2 of 3GPP 29.329
User-Identifier: [User-Name] [MSISDN]	Vendor-ID: none AVP code: 3102	Grouped	Section 6.4.2 of 3GPP 29.336
User-Name	Vendor-ID: none AVP code: 1	UTF8String	Section 8.14 of RFC 3588bis
MSISDN	Vendor-ID: 10415 (3GPP) AVP code: 701	OctetString	Section 6.3.2 of 3GPP 29.329
For a Routing Entity Type IPv4 Address
Framed-IP-Address	Vendor-ID: none AVP code: 8	OctetString	Section 6.11.1 of RFC 4005
For a Routing Entity Type IPv6 Prefix Address
Framed-IPv6-Prefix	Vendor-ID: none AVP code: 97	OctetString	Section 6.11.6 of RFC 4005

Each of the configured user identity types supported in RBAR is associated with certain AVPs that contain the user identity type as defined by various diameter application standards. Table 2-2 presents all possible combinations of the user identity types and the associated AVPs.

Table 2-2 Combinations of User Identity Types and Associated AVPs

User Identity Types/AVPs	IMSI	MSISDN	IMPI	IMPU
MSISDN		Applicable		Applicable
User-Identity: MSISDN		Applicable		Applicable
Public-Identity	Applicable	Applicable	Applicable	Applicable
User-Identity: Public-Identity	Applicable	Applicable	Applicable	Applicable
User-Name	Applicable	Applicable	Applicable	Applicable
User-Identifier: User-Name	Applicable		Applicable
User-Identifier: MSISDN		Applicable		Applicable
Subscription-ID-Data (0-E.164)		Applicable		Applicable
Service-Information: Subscription-ID-Data (0-E.164)		Applicable		Applicable
Subscription-ID-Data (1-IMSI)	Applicable		Applicable
Service-Information: Subscription-ID-Data (1-IMSI)	Applicable		Applicable
Subscription-ID-Data (2-SIP URI)	Applicable	Applicable	Applicable	Applicable
Service-Information: Subscription-ID-Data (2-SIP URI)	Applicable	Applicable	Applicable	Applicable
Subscription-ID-Data (3-NAI)	Applicable	Applicable	Applicable	Applicable
Service-Information: Subscription-ID-Data (3-NAI)	Applicable	Applicable	Applicable	Applicable
Subscription-ID-Data (4-Private)	Applicable	Applicable	Applicable	Applicable
Service -Information: Subscription-ID-Data (4-Private)	Applicable	Applicable	Applicable	Applicable
Wildcarded-Public-Identity				Applicable

A user identity type can be associated with one or more data formats that is examined when deriving the user identity address from the associated AVPs. The relation between user identity types and the corresponding data formats to be encountered in the ingress diameter request message are listed in Table 2-3.

Table 2-3 Relation between Configured User Identity Types and Data Formats

Configurable User Identity Types/User Identity Formats in Messages	IMSI	MSISDN	IMPI	IMPU
IMSI Format: ASCII Example: 311480123456789	Applicable		Applicable
MSISDN Format: ASCII and TBCD Example: 19194605500		Applicable		Applicable
SIP URI with IMSI Format: ASCII	Applicable		Applicable
Examples: sip:[e-mail] sip:[e-mail] sip:[e-mail] sip: [e-mail]
SIP URI with MSISDN Format: ASCII Examples: sip:[e-mail];user=phone sip:[e-mail]		Applicable		Applicable
SIP URI with NAI Format: ASCII Example: sip:[e-mail]			Applicable	Applicable
TEL URI with MSISDN FORMAT: ASCII		Applicable		Applicable
Examples: tel:[phone]; phone-context=example.com tel:[phone] tel:[phone]
NAI with IMSI/MSISDN Format: ASCII	Applicable	Applicable	Applicable	Applicable
Examples: [e-mail] 123456789012345 [e-mail] [e-mail] [e-mail]
NAI Format: ASCII Example: [e-mail]			Applicable	Applicable

Routing Based on IMSI/MSISDN Prefix Lookup

If configured, RBAR performs prefix-based lookups after the full address lookup is performed. The prefix and range based lookup is 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.

If a match is found in the prefix database, that RBAR application populates 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 RBAR performs 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.

Identifying IMSIs and MSISDNs

In certain diameter messages over the Cx interface (and possibly over the Sh interface), certain AVPs that typically carry an IMSI sometimes can carry an MSISDN.

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.

Most of the time, these applications can clearly categorize the decoded user identity based on:

• The configured routing entity type
• The contents of the AVP

  For instance, if the user identity has been decoded from a SIP URI that has a plus sign before the digits (such as sig:[e-mail]), it can be directly categorized as an MSISDN.

• The number of digits in the user identity

In certain cases, none of these methods allow a clear categorization (for example, if the number of digits needs to be used and the received number of digits are applicable to both IMSIs and MSISDNs, and thus leads to an ambiguous determination; or if there is no plus sign before the digits).

If RBAR has been configured to decode an IMPU/MSISDN from a user identity (digit string), but cannot determine whether the user identity is an IMSI or an MSISDN based on digit analysis, a tie-breaker is needed to properly categorize the user identity.

If the routing entity type is IMPU, the user identity extracted results in only digits and the length of the digits in the user identity falls within an overlap digits range of MSISDN and IMSI. As shown in Figure 2-1, if the user identity is an IMSI or MSISDN the logic is determined as follows:

• RBAR extracts the first 5 or 6 digits of the user identity and compares them against a list of configured 5- or 6-digit MCC-MNC combinations.

  The Diameter Common, and then Network Identifiers, and then MCCMNC pages can be used to configure up to 2500 distinct combinations of Mobile Country Code (MCC) and Mobile Network Code (MNC). (Refer to the Diameter Common User's Guide and Help for procedures to configure MCC-MNC combinations.)

• If a match occurs, the user identity is considered as an IMSI. RBAR bypasses the AVP, since RBAR does not support decoding an IMSI form a routing entity IMPU or MSISDN.
• If a match does not occur, the user identity is considered as a MSISDN and used for MSISDN lookup.

Figure 2-1 IMSI/MSISDN Overlap Range Scenario