Switching Systems
Private telephone switching systems are network devices that are small versions of telephone switching systems. Early key telephone switches used mechanical levers (crossbars) to interconnect lines. These were called key service units (KSUs). PBX systems use a time slot interchange (TSI) memory matrix to dynamically connect different communications paths through software control. Computer telephony and LAN telephony systems use packet switching systems to interconnect one of more telephone station with each other.
For large private telephone systems, some of the switching functions may be distributed to remote points. An example of distributed switching is the Nortel RPE that allows the Meridian PBX to remote a portion of its station interface to a remote site via a pair T1’s or E1’s.
Numbering Plan
Each extension in a private telephone system has a unique extension number. The station numbering plan for private telephone systems is controlled by the owner of the private telephone system. Many private systems have a limited range for extension numbers (e.g., 1000 -1999. This extension range is restricted due to hardware configurations.
When private telephone systems are interconnected to the public telephone network, the CCITT world numbering plan (E.164) and national numbering plans are used. PBX call processing systems are able to filter numbers to enable least cost routing (LCR). LCR is a telephone system feature that routes the connection of a call over the least expensive route available at the time the call is originated.
To allow automatic routing of incoming calls, direct inward dialing (DID), or higher-level trunk lines (e.g., T1 or E1) with advanced signaling may be used. DID connections are 2-wire trunk-side (network side) EO connections that provide additional information to the PBX to allow the automatic routing of calls within the PBX system. Although network signaling on incoming 2-wire circuits is primarily limited to one-way, incoming service, DID connections employ different supervision and address pulsing signals than dial lines. Typically, DID connections use a form of loop supervision called reverse battery, which is common for one-way trunk-side connections. Until recently, most DID trunks were equipped with either Dial Pulse (DP) or dual tone multifrequency (DTMF) address pulsing. While many carriers would have preferred to use multifrequency (MF) address pulsing, a number of LEC’s prohibited the use of MF on DID trunks.
Showing posts with label Numbering Plan. Show all posts
Showing posts with label Numbering Plan. Show all posts
Friday, April 25, 2008
Friday, March 21, 2008
PSTN: Numbering Plan
Numbering Plan
A numbering plan is a system that identifies communication points within a communications network through the structured use of numbers. The structure of the numbers is divided to indicate specific regions or groups of users. It is important that all users connected to a telephone network agree on a specific numbering plan to be able to identify and route calls from one point to another.
Telephone numbering plans throughout the world and systems vary dramatically. In some countries, it is possible to dial using 5 digits and others require 10 digits. To uniquely identify every device that is connected to public telephone networks, the Comite Consultatif Internationale de Telegraphique et Telehonique (CCITT) devised a world numbering plan that provides codes for telephone access to each country. These are called country codes. Coupled with the national telephone number assigned to each subscriber in a country, the country code telephone makes that subscribers number unique worldwide. The International Telecommunications Union (ITU) administers the World Numbering Plan standard E.164 publishes any new standards or modifications to existing standards on the Internet.
Each country defines its public telephone network numbering plans. The United States and Canada adopted the North American Numbering Plan (NANP) that allows the two countries to appear as one when dialing internally. Each country has a country code prescribed by the World
Numbering Plan so they are accessed internationally as separate entities. The NANP is based on 10 digit numbering (NXX-NXX-XXXX). The number consists of a 3-digit area code, a 3-digit central office code, and a 4-digit line number. The first three digits (NXX) are the Numbering Plan Area (NPA) or area code. It is this 3-digit code that designates one of the numbering plan areas in the North American Numbering Plan for direct distance dialing. Originally, the format was N0/1X, where N is any digit 2 through 9 and X is any digit. From 1995 on, the acceptable format is NXX.
With the massive requirement for telephone numbers generated by Internet access, fax machines, and cellular telephones, new area codes are being placed in service at an all time high rate. This is causing the telecommunications industry and standards bodies in North America to consider the implementation of “number portability”. When this occurs each subscriber will be assigned telephone numbers permanently (e.g., all subscribers in North America will dial ten digits to make a local call and take their number with them when they move.).
A numbering plan is a system that identifies communication points within a communications network through the structured use of numbers. The structure of the numbers is divided to indicate specific regions or groups of users. It is important that all users connected to a telephone network agree on a specific numbering plan to be able to identify and route calls from one point to another.
Telephone numbering plans throughout the world and systems vary dramatically. In some countries, it is possible to dial using 5 digits and others require 10 digits. To uniquely identify every device that is connected to public telephone networks, the Comite Consultatif Internationale de Telegraphique et Telehonique (CCITT) devised a world numbering plan that provides codes for telephone access to each country. These are called country codes. Coupled with the national telephone number assigned to each subscriber in a country, the country code telephone makes that subscribers number unique worldwide. The International Telecommunications Union (ITU) administers the World Numbering Plan standard E.164 publishes any new standards or modifications to existing standards on the Internet.
Each country defines its public telephone network numbering plans. The United States and Canada adopted the North American Numbering Plan (NANP) that allows the two countries to appear as one when dialing internally. Each country has a country code prescribed by the World
Numbering Plan so they are accessed internationally as separate entities. The NANP is based on 10 digit numbering (NXX-NXX-XXXX). The number consists of a 3-digit area code, a 3-digit central office code, and a 4-digit line number. The first three digits (NXX) are the Numbering Plan Area (NPA) or area code. It is this 3-digit code that designates one of the numbering plan areas in the North American Numbering Plan for direct distance dialing. Originally, the format was N0/1X, where N is any digit 2 through 9 and X is any digit. From 1995 on, the acceptable format is NXX.
With the massive requirement for telephone numbers generated by Internet access, fax machines, and cellular telephones, new area codes are being placed in service at an all time high rate. This is causing the telecommunications industry and standards bodies in North America to consider the implementation of “number portability”. When this occurs each subscriber will be assigned telephone numbers permanently (e.g., all subscribers in North America will dial ten digits to make a local call and take their number with them when they move.).
Subscribe to:
Posts (Atom)