On numbering plan for one network in one country, there 3 ways that usually used, that is:
- Opened numbering
- Closed numbering
- Combination numbering
On opened numbering system, area code only used when to perform long distance connection (trunk), event though to build connection with the local customer, just to dial the customer number destination. This numbering system usually used by country that:
- Large area
- Comparison the local connection is more higher then toll/trunk connection.
- Local area limits that one with other is clear.
The example of country that using opened numbering system is Indonesia, which to perform long distance call, the caller first to dial digit “0”, then followed area code and ended with destination customer number.
Example A that living in Bandung want to call B that stay in Jakarta with telephone number 8602345. The number that dialed by A is 021-8602345, where first digit “0” to represent prefix trunk and digit “ 21” is area code Jakarta.
On closed numbering system, area code is direct (joined) combined with customer telephone number. So that on this system there is no different between local connection and trunk, because every call must always to dial code area (without trunk prefix), then followed with customer telephone number. Closed numbering usually used by country that small area so that no need the trunk connection. Example, the country that using this system is Singapore.
