What is MSISDN Mobile Station International Subscriber Directory Number

Technical details of the Mobile Station International Subscriber Directory Number (MSISDN).

1. Definition:
   • The MSISDN is a unique identifier used in mobile networks to represent a mobile phone user.
   • It consists of three main components:
     • Country Code (CC): A numerical code that identifies the country or geographical area.
     • National Destination Code (NDC): Part of the number that characterizes the subscriber’s operator within the country.
     • Subscriber Number (SN): The specific number assigned to an individual mobile user.
   • Together, these components globally distinguish a specific mobile subscriber.
2. Purpose and Usage:
   • The MSISDN serves several critical purposes:
     • Routing Calls: When someone dials a phone number, the MSISDN is used to route the call to the correct mobile phone.
     • Subscriber Identification: It uniquely identifies a subscription in a Global System for Mobile Communications (GSM) or Universal Mobile Telecommunications System (UMTS) network.
     • Mapping to SIM: The MSISDN maps to the subscriber identity module (SIM) in a mobile phone.
3. Interpretations:
   • The abbreviation “MSISDN” has several interpretations, with the most common one being “Mobile Station International Subscriber Directory Number.”
   • It is also known as the “Mobile Subscriber ISDN Number.”
4. Format:
   • The ITU-T recommendation E.164 defines the maximum length of an MSISDN as 15 digits.
   • The format includes:
     • Country Code: 1-3 digits reserved for the country code.
     • National Destination Code: Identifies the operator within the country.
     • Subscriber Number: The unique number assigned to the mobile user.
   • Example MSISDN: +880 15 00121121 (Teletalk Hotline Number)
     • MSISDN = 8801500121121
     • CC = 880 (Bangladesh country code)
     • NDC = 15 (Teletalk operator code)
     • SN = 00121121
5. Changeability:
   • A SIM has a unique IMSI (International Mobile Subscriber Identity) that remains constant.
   • However, the MSISDN can change over time, meaning different MSISDNs can be associated with the same SIM.