mathematics

MSISDN

MSISDN is a mathematics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand MSISDN rather than just read about it. In short: MSISDN () is a number uniquely identifying a subscription in a Global System for Mobile communications or a Universal Mobile Telecommunications System mobile network. It is the mapping of the telephone number to the subscriber identity module in a mobile or cellular phone.

Key takeaways

MSISDN belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MSISDN to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MSISDN from memory before moving on to harder problems.

Reference excerpt

MSISDN () is a number uniquely identifying a subscription in a Global System for Mobile communications or a Universal Mobile Telecommunications System mobile network. It is the mapping of the telephone number to the subscriber identity module in a mobile or cellular phone. This abbreviation has several interpretations, the most common one being "Mobile Station International Subscriber Directory Number". The MSISDN and international mobile subscriber identity (IMSI) are two important numbers used for identifying a mobile subscriber. The IMSI is stored in the SIM (the card inserted into the mobile phone), and uniquely identifies the mobile station, its home wireless network, and the home country of the home wireless network. The MSISDN is used for routing calls to the subscriber. The IMSI is often used as a key in the home location register ("subscriber database") and the MSISDN is the number normally dialed to connect a call to the mobile phone. A SIM has a unique IMSI that does not change, while the MSISDN can change in time, i.e. different MSISDNs can be associated with the SIM. The MSISDN follows the numbering plan defined in the International Telecommunication Standard Sector recommendation E.164.

Abbreviation Depending on source or standardization body, the abbreviation MSISDN can be written out in several different ways. These are today the most widespread and common in use.

MSISDN format The ITU-T recommendation E.164 limits the maximum length of an MSISDN to 15 digits. 1-3 digits are reserved for country code. Prefixes are not included (e.g., 00 prefixes an international MSISDN when dialing from Sweden). Minimum length of the MSISDN is not specified by ITU-T but is instead specified in the national numbering plans by the telecommunications regulator in each country. In GSM and its variant DCS 1800, MSISDN is built up as

MSISDN = CC + NDC + SN CC = Country Code NDC = National Destination Code, identifies one or part of a PLMN SN = Subscriber Number In the GSM variant PCS 1900, MSISDN is built up as

MSISDN = CC + NPA + SN CC = Country Code NPA = Number Planning Area SN = Subscriber Number The country code identifies a country or geographical area, and may be between 1-3 digits. The ITU defines and maintains the list of assigned country codes.

Example Example Number: +880 15 00121121 (Teletalk Hotline Number) Has the following subscription number: MSISDN=8801500121121MSISDN=CCCXXN1N2N3N4N5N6N7N8

For further information on the MSISDN format, see the ITU-T specification E.164.

See also E.164 International Mobile Equipment Identity (IMEI) International Mobile Subscriber Identity (IMSI) SIM card Mobile phone GSM HLR E.214 Mobile identification number Telephone number

References

External links http://www.3gpp.org, GSM 03.03 (see section 3.3) http://www.openmobilealliance.org http://www.itu.int, E.164, E.212, E.213, E.214 https://web.archive.org/web/20110222090438/http://www.gsmworld.com/

Illustrations

Worked examples

Example 1 — a first encounter with MSISDN

Start with the simplest possible case. Write down what MSISDN claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to MSISDN before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about MSISDN ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of MSISDN

In research: MSISDN appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses MSISDN in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: MSISDN is common in secondary-school and first-year university syllabi. It links to neighbouring topics ITU-T recommendations, Identifiers, Telephone numbers, so understanding it makes those chapters shorter.
In everyday life: Look for MSISDN outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study MSISDN in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MSISDN means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain MSISDN out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MSISDN in simple terms?

Why does MSISDN matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study MSISDN?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on MSISDN.