What is MSISDN Mobile Subscriber Integrated Services Digital Network Number

Technical details of the MSISDN (Mobile Subscriber Integrated Services Digital Network Number):

1. Definition:
   • The MSISDN is a unique identifier assigned to a mobile phone user within a mobile network.
   • It serves as a mapping between the telephone number and the subscriber identity module (SIM) in a mobile or cellular phone.
2. Interpretation:
   • The abbreviation MSISDN can be expanded in different ways, but the most common interpretation is “Mobile Station International Subscriber Directory Number.”
   • It plays a crucial role in routing calls to the subscriber.
3. Components:
   • The MSISDN consists of the following components:
     • Country Code (CC): A numerical code representing the country or geographical area.
     • National Destination Code (NDC): Identifies a specific part of a Public Land Mobile Network (PLMN).
     • Subscriber Number (SN): The individual phone number assigned to the user.
4. Format:
   • The ITU-T recommendation E.164 defines the maximum length of an MSISDN as 15 digits.
   • The format varies slightly depending on the mobile network technology:
     • In GSM and its variant DCS 1800, the MSISDN is built as:MSISDN = 88 + 017 + SN CC = Country Code (e.g., 88) NDC = National Destination Code (e.g., 017) SN = Subscriber Number
     • In the GSM variant PCS 1900, the MSISDN is built similarly:MSISDN = 88 + 017 + SN CC = Country Code NPA = Number Planning Area (e.g., 017) SN = Subscriber Number
5. Uniqueness:
   • The IMSI (International Mobile Subscriber Identity) is another important number used for identifying a mobile subscriber. However, unlike the IMSI, which is stored in the SIM and remains constant, the MSISDN can change over time.
   • Different MSISDNs can be associated with the same SIM.
6. Role:
   • The MSISDN is used for connecting calls to the mobile phone.
   • It is often used as a key in the Home Location Register (HLR) or subscriber database.