What is a mobile subscriber ISDN number (MSISDN)?

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A Mobile Subscriber ISDN Number (MSISDN) is essentially what most people recognize as their "phone number" – the unique identifier used to directly call or send an SMS message to a mobile subscriber in a telecommunication network. While the abbreviation has several interpretations, the most common and widely accepted is "Mobile Station International Subscriber Directory Number."


The MSISDN is a crucial component in ensuring seamless communication within a mobile network and across global telecommunications. It adheres to the ITU-T Recommendation E.164 numbering plan, which specifies the structure and maximum length of international telephone numbers. An MSISDN can have a maximum length of 15 digits.



Components of an MSISDN:
An MSISDN is composed of three main parts:

Country Code (CC): This is the first part of the number, typically 1 to 3 digits long, which identifies the country of the mobile subscriber. For example, 880 for Bangladesh, 1 for the USA and Canada, or 44 for the United Kingdom. These codes are assigned by the ITU.

National Destination Code (NDC): This part identifies the specific mobile dentist phone number list network operator or a geographical area within a country. It varies in length depending on the national numbering plan. In Bangladesh, for instance, codes like 017 (for Grameenphone) or 018 (for Robi) are NDCs within the 880 country code (when dialing nationally, the 0 is typically used as a national prefix before the NDC, but the MSISDN itself includes the 880 and then the NDC).
Subscriber Number (SN): This is the unique part of the number that identifies the individual subscriber within the specific network identified by the NDC. Its length depends on the country's numbering plan and the NDC's length, ensuring the total MSISDN does not exceed 15 digits.
So, the format is typically: MSISDN = CC + NDC + SN.

MSISDN vs. IMSI:
It's important to distinguish the MSISDN from another crucial identifier, the International Mobile Subscriber Identity (IMSI):

MSISDN: This is the public number that users dial to reach a subscriber. It's the number you give to friends, family, and businesses. A single SIM card can, in some cases, be associated with multiple MSISDNs (e.g., if a user has multiple numbers on one SIM), or an MSISDN can be transferred between SIMs (e.g., through mobile number portability).
IMSI: This is a technical, internal identifier stored on the SIM card itself. It uniquely identifies the subscriber within the network and is used by network operators for authentication, routing, and network management. You cannot dial an IMSI. The IMSI consists of the Mobile Country Code (MCC), Mobile Network Code (MNC), and Mobile Subscriber Identification Number (MSIN). While the IMSI is tied to the SIM, the MSISDN is tied to the subscription and can be ported.


Purpose and Usage:
The MSISDN serves several critical purposes in mobile communications:

Call and SMS Routing: Its primary function is to act as the unique address for routing voice calls and SMS messages to the correct mobile device.
Subscriber Identification: It identifies a mobile subscriber on a network for billing, service provisioning, and customer support.
Customer Interaction: It's the number customers use to interact with an organization, whether for support, sales, or other services.
IoT Devices: In the context of the Internet of Things (IoT), MSISDNs are assigned to connected devices (like smart meters or telematics units) that require cellular connectivity, enabling them to communicate within the network.
In essence, the MSISDN is the user-facing phone number that facilitates communication, while the IMSI is the network's internal way of identifying the specific SIM and, by extension, the subscriber for technical operations.