Number range holder network of the B subscriber

Description

The NPLMN (Number range holder PLMN) is a specific type of Public Land Mobile Network (PLMN) identifier used in telecommunication routing and billing logic. It does not identify the network where a subscriber is currently roaming or being served; instead, it identifies the network that originally owned or was assigned the block of Mobile Subscriber ISDN Numbers (MSISDNs) to which the called party's (B-subscriber's) number belongs. This concept becomes critically important in the context of Mobile Number Portability (MNP), where a subscriber can change service providers while retaining their old phone number.

Architecturally, the NPLMN is a data point stored in network databases, notably in Number Portability databases (NPDBs) or as an attribute within the Home Location Register (HLR). When a call is made to a ported number, the originating network's Gateway MSC (GMSC) performs a number portability query. The response includes routing information (the recipient network's PLMN, or RNPLMN) and often the NPLMN for billing and settlement purposes. The NPLMN is typically represented as a Mobile Country Code (MCC) and Mobile Network Code (MNC), just like a standard PLMN ID.

In the call flow, the GMSC uses the RNPLMN to route the call to the network currently serving the B-subscriber. However, the NPLMN is used in the generation of Call Detail Records (CDRs) for inter-operator billing and settlement. Since the calling party's network may have different tariff agreements with the number range holder (NPLMN) versus the actual service provider (RNPLMN), correctly identifying both is essential for accurate financial transactions. The NPLMN ensures that revenue for calls to ported numbers can be appropriately distributed between the ported-to operator (who provides service) and the range-holder operator (who may provide interconnection or other services). Its role is purely in the administrative and business layers of network operation, ensuring the economic model of number portability functions correctly.

Purpose & Motivation

The NPLMN concept was created specifically to address the business and operational challenges introduced by Mobile Number Portability (MNP). Before MNP, a subscriber's MSISDN was permanently tied to their service provider's network (the HPLMN). Routing and billing were straightforward: the MSISDN's numbering range directly indicated the home network. MNP broke this direct link, allowing a subscriber to take their number to a different operator. This created a problem: how does the industry track which operator originally owned the number for purposes like interconnection fee settlements, billing, and regulatory reporting?

The NPLMN solves this by permanently associating a number with the PLMN that was initially allocated that number range by the national numbering authority. This provides a fixed, immutable reference point in the ecosystem. Without the NPLMN, there would be no consistent way to determine the "original" operator for a ported number, complicating financial settlements and making it difficult to administer numbering resources. It allows the industry to separate the concepts of "service provision" (handled by the RNPLMN) and "number range ownership/responsibility" (handled by the NPLMN).

This distinction is crucial for fair compensation. Interconnection fees or termination rates might be contractually agreed based on the identity of the number range holder. The NPLMN enables accurate CDR generation so that these agreements can be honored even after a number ports. It also aids in fraud detection and regulatory oversight, as it provides a trail back to the entity initially responsible for the number. In essence, the NPLMN is a key enabler for the sustainable commercial and regulatory framework that makes widespread number portability feasible.

Key Features

• Identifies the PLMN that holds the original MSISDN numbering range for a subscriber
• A critical data element for operations under Mobile Number Portability (MNP)
• Used primarily for inter-operator billing, settlement, and CDR generation
• Distinct from the Recipient Network PLMN (RNPLMN) which is used for call routing
• Stored in Number Portability Databases (NPDB) and used in portability query responses
• Represented as a standard PLMN ID (MCC+MNC)

Evolution Across Releases

Defining Specifications