Understanding PLMN: Public Land Mobile Network

Understanding PLMN: Public Land Mobile Network

A Public Land Mobile Network (PLMN) is the complete infrastructure operated by a single mobile network operator to provide terrestrial mobile telecommunications services. More commonly, the term PLMN is used to refer to the unique identifier assigned to each mobile network operator's network.

PLMN Identifier Structure

The PLMN identifier is a combination of two components:

PLMN = MCC + MNC

Where:

• MCC (Mobile Country Code): A three-digit code identifying the country
• MNC (Mobile Network Code): A two or three-digit code identifying the specific network operator

For example, the PLMN identifier 310410 breaks down as:

• 310: MCC for the United States
• 410: MNC for AT&T

PLMN in Network Operations

PLMNs serve several critical functions in mobile telecommunications:

1. Network Identification and Selection

• Mobile devices use PLMN identifiers to distinguish between different networks
• The device compares available PLMNs against its preferred PLMN list stored on the SIM
• This determines which network the device attempts to connect to first

2. Roaming Management

• When a subscriber roams internationally, the visited network identifies the home network using the PLMN
• Roaming agreements between operators are established based on PLMN identifiers
• Authentication and billing information is exchanged between networks using PLMNs as reference

3. Interconnection

• PLMNs identify networks for interconnection purposes
• Call routing between different mobile networks relies on PLMN identification
• Inter-operator billing and settlements use PLMNs for accounting

PLMN Broadcasting and Discovery

Mobile networks broadcast their PLMN identifiers to enable device connection:

Cell Broadcast Information

• Base stations continuously broadcast their PLMN identifier
• This allows mobile devices to identify which networks are available
• Signal strength measurements are associated with specific PLMNs

Network Scanning

• When a mobile device performs a network scan, it detects available PLMNs
• The device displays these as available networks to the user
• In automatic mode, the device selects the appropriate PLMN based on preferences

PLMN in Different Network Technologies

The use of PLMN identifiers has evolved across generations of mobile technology:

2G (GSM) Networks

• PLMNs were first standardized with GSM technology
• Simple PLMN-based network selection
• Limited to voice and basic data services

3G and 4G Networks

• Enhanced PLMN selection algorithms
• Support for multiple radio access technologies under the same PLMN
• More sophisticated preferred PLMN lists with technology preferences

5G Networks

• Continued use of PLMN identifiers for network identification
• Support for network slicing within a single PLMN
• Enhanced security for PLMN selection to prevent spoofing

PLMN in Network Sharing Scenarios

As operators increasingly share infrastructure, PLMN handling has become more complex:

Multi-Operator Core Networks (MOCN)

• Multiple operators share radio access network (RAN) infrastructure
• Each operator maintains its own distinct PLMN
• The shared RAN broadcasts multiple PLMN identifiers

Multi-Operator Radio Access Network (MORAN)

• Operators share physical infrastructure but maintain separate radio carriers
• Each carrier broadcasts its own PLMN
• Devices connect to the appropriate carrier based on PLMN

National Roaming

• One operator's subscribers use another operator's network in specific regions
• The device connects to a different PLMN than its home PLMN
• Special configurations enable this domestic roaming capability

Regulatory Aspects of PLMNs

PLMNs are subject to regulatory oversight:

• National regulatory authorities assign MNCs within their country
• Regulations may govern PLMN selection to ensure fair competition
• Emergency call handling may override normal PLMN selection rules
• Some countries require registration of all PLMNs operating within their territory

PLMN in Consumer Experience

From a user perspective, PLMNs typically appear as:

• Network names displayed on the device (e.g., "AT&T", "Vodafone")
• These display names are mapped to PLMNs in the device's software
• When selecting networks manually, users choose from a list of available PLMNs
• Network signal indicators show connection status to the current PLMN