--- title: "National and international numbering plans" subject: "Telecommunications" chapter: 7 key: "semester_8/telecommunications:numbering-plan-national-international" source: https://www.bctengineer.com/q/semester_8/telecommunications/numbering-plan-national-international site: BCT Engineering --- # National and international numbering plans Telecommunications · Chapter 7: Telecommunication Regulation - Asked in: 2081 Baisakh, 2+6 marks; 2076 Chaitra, 8 marks; 2073 Chaitra, 8 marks (asked 3 times) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/numbering-plan-national-international - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-7 ## Question What is numbering plan? Explain national and international numbering plan with different types and examples in detail. ## Short answer A numbering plan allocates unique numbers for routing; types include open (variable length, trunk prefix) and closed (fixed length, no trunk prefix). National numbers use trunk prefix, area code, and subscriber number; international E.164 numbers have country code plus national significant number, max 15 digits, e.g. Nepal +977 1 4412345. ## Answer A **numbering plan** is a scheme for allocating unique numbers to subscribers, exchanges, areas and countries, so that every telephone in the world can be reached and the switches can route a call from the dialled digits. It also fixes the number length, prefixes and special codes. #### Requirements of a good numbering plan - A unique number for every subscriber. - Easy for users to remember and dial. - Allows routing and charging from the digits. - Room for future growth without renumbering. - Follows ITU-T recommendation **E.164**. #### Types of numbering plan 1. **Open numbering plan.** Number length varies; a trunk prefix is dialled for calls outside the local area (e.g. 0 + area code). Used in Nepal, the UK and India. 2. **Closed numbering plan.** All numbers in the country have the same length and the full number is always dialled; there is no trunk prefix. Examples: USA/Canada (NANP, 10 digits), Singapore (8 digits). 3. **Uniform numbering:** all subscribers have the same number length. 4. **Non-uniform numbering:** different areas use different subscriber number lengths. #### National numbering plan A national number consists of ```text [Trunk prefix] [Area/trunk code] [Exchange code] [Line no.] 0 1 44 12345 ``` - **Trunk prefix (0):** tells the exchange that a long-distance call follows. - **Area (trunk) code:** identifies the numbering area. - **Subscriber number:** exchange code + line number. - **National significant number (NSN)** = area code + subscriber number. Examples in Nepal: Kathmandu 01-4XXXXXX, Pokhara 061-5XXXXX, Biratnagar 021-XXXXXX; mobile numbers have 10 digits, e.g. 984XXXXXXX (Nepal Telecom), 980XXXXXXX (Ncell); special codes 100 (police), 101 (fire), 102 (ambulance). #### International numbering plan (ITU-T E.164) ```text [International prefix] [CC] [National significant number] 00 977 1 4412345 ``` - **International prefix:** dialled to leave the country (00 in Nepal and most countries, 011 in North America; written as "+"). - **Country code (CC):** 1 to 3 digits; the first digit gives the world zone. - **NSN:** area code + subscriber number, without the trunk prefix. - The maximum length of the international number (CC + NSN) is **15 digits**. World numbering zones: | Zone | Region | Example | |---|---|---| | 1 | North America (NANP) | +1 USA | | 2 | Africa | +27 South Africa | | 3, 4 | Europe | +44 UK | | 5 | South/Central America | +55 Brazil | | 6 | Southeast Asia and Oceania | +61 Australia | | 7 | Russia, Kazakhstan | +7 | | 8 | East Asia, special services | +81 Japan | | 9 | West, Central and South Asia, Middle East | +91 India, +977 Nepal | **Example:** a Kathmandu number 01-4412345 called from abroad is dialled as 00-977-1-4412345 (written +977 1 4412345); from Pokhara it is dialled 01-4412345; from within Kathmandu, just 4412345. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main purpose of a numbering plan? A. To allocate frequencies to operators B. To fix tariffs for calls C. To give every subscriber a unique number so calls can be routed and charged from the digits D. To measure traffic in erlang Answer: C. A numbering plan allocates unique numbers so exchanges can route and charge from dialled digits. (Key point: Numbering plan purpose) 2. Which describes a closed numbering plan? A. Variable number length with trunk prefix, as in Nepal B. All numbers have the same length and the full number is always dialled, as in USA/Canada C. Numbers only for international calls D. Numbers using only emergency codes Answer: B. Closed plans have fixed length and no trunk prefix; open plans use varying lengths and a trunk prefix. (Key point: Open vs closed plan) 3. The maximum length of an international number under E.164 (CC + NSN) is: A. 10 digits B. 12 digits C. 15 digits D. 20 digits Answer: C. E.164 limits CC plus NSN to 15 digits. (Key point: E.164 length) 4. A Kathmandu number 01-4412345 is dialled from abroad as: A. 00-977-1-4412345 (trunk 0 dropped) B. 00-977-01-4412345 C. 977-01-4412345 without prefix D. 01-977-4412345 Answer: A. Use the international prefix and country code 977, and drop the national trunk prefix 0. (Key point: International dialling) ## Related in Telecommunications - [ITU roles and numbering plans](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aitu-roles-numbering-plan) — Telecommunications, chapter 7 - [Traffic intensity, GOS and national numbering](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Atraffic-intensity-gos-numbering) — Telecommunications, chapter 6 - [NTA's role and ITU numbering plan](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Anta-role-itu-numbering) — Telecommunications, chapter 7 - [Short note: Telephone numbering in PSTN](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Ashort-note-pstn-numbering) — Telecommunications, chapter 7, asked 2× - [GOS vs blocking probability; E.164 plan](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Agos-vs-blocking-e164) — Telecommunications, chapter 6 ## Related in other subjects - [National parks, forests and climate resilience](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Anational-parks-climate-resilience) — Technology, Environment and Society, chapter 6