MSISDN
The Mobile Station International Subscriber Directory Number (MSISDN) is a unique telephone number assigned to a mobile subscription in cellular networks, such as those based on GSM, UMTS, LTE, and 5G standards, serving as the primary public identifier for routing voice calls, short message service (SMS), and other telecommunication services to the subscriber's device.[1] Structured according to the ITU-T E.164 international numbering plan, an MSISDN consists of a country code (CC), followed by a national significant number that includes a national destination code (NDC) and a subscriber number (SN), with a maximum length of 15 digits to ensure global uniqueness and compatibility.[1][2] Unlike the internal International Mobile Subscriber Identity (IMSI), which is a private network identifier composed of a mobile country code (MCC), mobile network code (MNC), and mobile subscriber identification number (MSIN), the MSISDN is publicly visible and linked to the IMSI in the Home Location Register (HLR) or Home Subscriber Server (HSS) for service provisioning and authentication.[1] This linkage allows for features like number portability, where the MSISDN can remain associated with a subscriber even if the IMSI changes, and supports multiple MSISDNs per IMSI for advanced services such as multi-numbering.[1] MSISDNs are mandatory for most Public Land Mobile Network (PLMN) subscribers accessing circuit-switched domain services but may be optional for packet-switched-only subscriptions, playing a critical role in roaming, emergency calling, and integration with IP Multimedia Subsystem (IMS) for multimedia communications.[1]Definition
Abbreviation and Meaning
MSISDN stands for Mobile Station International Subscriber Directory Number. This term encapsulates a unique identifier in mobile telecommunications, formally defined in standards developed for global mobile networks.[3] The core concept of an MSISDN is that it serves as the unique, dialable telephone number assigned to a mobile subscriber, enabling identification and routing within public telecommunication networks. It functions as the primary directory number for reaching a subscriber's mobile station from external networks, such as the public switched telephone network (PSTN).[3] Etymologically, "Mobile Station" refers to the user's mobile equipment or device in the network; "International" denotes its adherence to a global numbering plan with worldwide scope; and "Subscriber Directory Number" aligns with ITU standards for directory-accessible numbers used in subscriber services, structured according to Recommendation E.164. This breakdown reflects the identifier's role in integrating mobile users into international directory and routing systems.[2][3] MSISDN was introduced as part of the adaptations of Integrated Services Digital Network (ISDN) principles for mobile telephony, specifically within the framework of the Global System for Mobile communications (GSM) to support digital mobile subscriber numbering.[3][2]Purpose in Telecommunications
The MSISDN, or Mobile Station International Subscriber Directory Number, primarily functions as the unique telephone number assigned to a mobile subscriber, enabling the routing of incoming voice calls and short message service (SMS) messages to the appropriate device within the network.[3] In mobile network operations, when an incoming call or SMS is directed to an MSISDN, the gateway mobile switching center (GMSC) queries the home location register (HLR) to obtain routing information, such as the mobile station roaming number (MSRN), ensuring delivery to the subscriber's current location. This process relies on the signaling system No. 7 (SS7) protocol, specifically the mobile application part (MAP), for call setup and location updates, allowing the network to track and connect the subscriber dynamically. Beyond routing, the MSISDN serves as the external identifier for essential network services, including billing, roaming, and directory inquiries. Operators use it to generate charging data records (CDRs) that associate usage—such as call duration, data volume, or SMS counts—with the subscriber for accurate invoicing. In roaming scenarios, the MSISDN identifies the subscriber across visited networks, enabling seamless connectivity and settlement between home and foreign operators through standardized protocols. Unlike internal identifiers like the IMSI, which remain hidden for security, the MSISDN is publicly known and directly used by end-users to initiate or receive communications.[3] As an E.164-compliant number, the MSISDN promotes global interoperability among mobile networks, allowing users to maintain consistent numbering and service access worldwide.[2] It also underpins value-added services by providing a reliable endpoint for SMS-based applications, such as one-time password (OTP) delivery for authentication in mobile banking or secure transactions. This utility extends to directory services, where the MSISDN links subscriber profiles for features like caller ID or contact resolution, enhancing overall network efficiency and user experience.Structure
Format and Components
The Mobile Station International Subscriber Directory Number (MSISDN) follows the international public telecommunication numbering plan outlined in ITU-T Recommendation E.164, which specifies a maximum length of 15 digits for global uniqueness and routability in public networks.[2] This format ensures compatibility with integrated services digital network (ISDN) and public switched telephone network (PSTN) systems, treating MSISDN as a standard E.164 telephone number assigned to mobile subscribers.[4] The MSISDN is composed of three primary components: the country code (CC), the national destination code (NDC), and the subscriber number (SN). The country code is a 1- to 3-digit prefix identifying the country of registration, such as 1 for the United States or 49 for Germany.[4][2] The national destination code, which varies by country from 1 to 4 or more digits, follows the CC and identifies the mobile network operator or service area within the country, with multiple NDCs possible per public land mobile network (PLMN) in some regions.[4] The subscriber number, comprising the remaining digits to fit within the national plan (often 6 to 9 digits but varying), uniquely identifies the individual subscriber within that operator's network and may incorporate additional routing digits if needed.[4] Parsing an MSISDN adheres to strict rules defined in E.164 to maintain international consistency. In the international format, the number begins with a plus sign (+) followed by the CC without leading zeros, and the total digit count excludes any optional sub-address (up to 20 octets) that might be appended for further addressing.[2] National lengths vary by country due to differing numbering plans; for instance, the United States uses a 10-digit national number (CC + 10 digits total), while Germany employs a 10-digit national significant number for mobile (CC + 10 digits total).[2] These variations ensure the overall structure remains within the 15-digit limit while accommodating local requirements.[4]International Standardization
The international standardization of the Mobile Station International Subscriber Directory Number (MSISDN) is overseen by the International Telecommunication Union - Telecommunication Standardization Sector (ITU-T), a specialized agency of the United Nations responsible for developing global telecommunication standards.[2] The ITU-T defines MSISDN within its Recommendation E.164, titled "The international public telecommunication numbering plan," which establishes a uniform framework for international telephone numbering, including MSISDN as a subset of international Integrated Services Digital Network (ISDN) numbers.[2] This recommendation ensures that MSISDNs adhere to a consistent global structure, facilitating seamless communication across diverse networks and borders.[2] Under E.164, the allocation process begins with the ITU-T assigning country codes (typically 1 to 3 digits) to individual countries, geographic regions, or global services, creating a hierarchical system that prevents overlaps and supports international dialing.[5] National Destination Codes (NDCs) and subscriber numbers are then managed by national regulatory authorities within each country, which oversee the distribution to mobile network operators while complying with ITU-T guidelines.[6] For instance, in the United States, the Federal Communications Commission (FCC) administers the allocation of these national components under the North American Numbering Plan, ensuring efficient use and availability of numbers for mobile services.[6] This standardization framework guarantees the uniqueness of MSISDNs worldwide and promotes interoperability among international telecommunication systems, enabling reliable routing of calls, messages, and data services.[2] E.164 has undergone periodic updates to address evolving technologies and demands; the latest major revision was published in June 2020, with Amendment 1 issued in June 2011 to clarify aspects such as number structure and functionality, and ongoing supplements handle specific applications like number portability.[2]Examples
To illustrate the MSISDN structure in practice, consider the format used in the United States, where the country code is +1, followed by a 3-digit national destination code (NDC) for mobile networks, such as 201, and a 7-digit subscriber number, resulting in an example like +1 201 123 4567.[2] In the United Kingdom, the MSISDN begins with the country code +44, a mobile NDC like 7911 (4 digits), and a 6-digit subscriber number, as in +44 7911 123456.[2] For India, the country code +91 precedes a 2-digit mobile NDC such as 98, followed by an 8-digit subscriber number, forming a full international MSISDN like +91 98XXX XXXXXX; nationally, this corresponds to a 10-digit number without the leading zero.[2] Variations in formatting often involve handling leading zeros in national numbers: for instance, in Germany, a national mobile number starting with 0151 (including the trunk zero) becomes +49 151 123 4567 internationally, dropping the internal zero while retaining the 3-digit NDC 151 and 7-digit subscriber number.[2]Relation to Other Identifiers
Comparison with IMSI
The International Mobile Subscriber Identity (IMSI) is a unique identifier allocated to each mobile subscriber in GSM, UMTS, EPS, and 5GS networks, consisting of up to 15 decimal digits and stored on the SIM card for authentication and network access purposes.[7] Unlike the MSISDN, which serves as a public, dialable telephone number for routing calls and messages in the public switched telephone network (PSTN), the IMSI functions as a private, internal identifier solely for network operations such as subscriber management, roaming, and access control, and is not directly accessible or dialable by end users.[7] A primary distinction lies in their visibility and usage: the MSISDN is externally visible and routable, enabling public communication to a subscriber, whereas the IMSI remains concealed within the network to protect subscriber privacy and is used exclusively for internal processes like authentication without exposure to external entities.[7] This separation ensures that while the MSISDN facilitates user-facing services, the IMSI supports secure, backend network functions without compromising anonymity in public interactions.[7] In terms of structure, the IMSI comprises a Mobile Country Code (MCC, 3 digits), Mobile Network Code (MNC, 2 or 3 digits), and Mobile Subscriber Identification Number (MSIN, the remaining 9 or 10 digits), forming a fixed, globally unique code tied to the subscriber's identity across networks.[7] By contrast, the MSISDN follows the ITU-T E.164 international public telecommunication numbering plan, structured as a country code (CC, 1-3 digits), national destination code (NDC, variable), and subscriber number (SN, variable), up to 15 digits total, optimized for public dialing rather than internal network coding.[7] There is no fixed one-to-one mapping between the two; instead, they are linked dynamically through the subscriber's profile in the network's home location register (HLR) or equivalent database.[7] Notably, a single IMSI can be associated with multiple MSISDNs, allowing one subscriber to maintain several public numbers—such as for multi-SIM setups, virtual numbering services, or distinct profiles for voice, data, or supplementary services—while the IMSI remains the unchanging core identifier for the subscription.[7] This flexibility supports advanced subscriber management without altering the fundamental authentication identity.[7]| Aspect | MSISDN | IMSI |
|---|---|---|
| Primary Role | Public routing and dialing for calls/SMS | Internal authentication and subscriber management |
| Visibility | External and user-facing | Network-internal and private |
| Dialability | Yes, follows E.164 plan | No |
| Structure | CC (1-3) + NDC + SN (up to 15 digits total) | MCC (3) + MNC (2-3) + MSIN (9-10) |
| Mapping | Multiple per IMSI possible | One per subscriber, fixed |