Numbering Plan Administration (NPA)
In order for any telephone to connect to any other telephone in the world, there must be in place a carefully developed and administered numbering plan. or logical addressing scheme. The ITU-T is responsible for numbering plan administration at the international level, with each nation or region having similar responsibility within its domain. For instance, Bellcore is responsible for the North American Numbering Plan (NANP), which was established in 1947 as a means of integrating the area code and central office exchange codes in the United States, Canada, and the Caribbean. Within each state in the United States, the dominant LEC (Local Exchange Carrier) read “BOC” administers the NANP [6-3].
The current international NPA convention specifies 12 digits, although the number of digits required for calling within a nation varies. In many cases, numbering schemes vary within the same country-for instance, six- and seven-digit telephone numbers co-exist in Australia during the period of transition to a full seven-digit convention. The ITU-T plans to implement a 15-digit international dialing scheme in 1996.
When dialing a telephone number, the user, in effect, is instructing the network to establish a connection between two physical addresses based on a logical address. Using a familiar example, the following logical addressing convention is followed establishing a connection originating from a physical address in Australia and terminating at another associated with this author’s business, The Context Corporation at 1500A East College Way, Suite 443, Mt. Vernon, WA, 98273 USA, at 0015.1.360.336.3448:
- 0015: 00 indicates that the call is international; 15 is the country code for the U.S.
- 1+ usually indicates that the call is crossing a Numbering Plan Area (NPA), or Area Code, boundary
- 360 indicates the NPA, or Area Code, which is a physical location-specifically, the area of western Washington surrounding the Greater Seattle metropolitan area and which happens to be in LATA 674.
- 336 indicates a specific Mt. Vernon central office exchange. These three digits are associated with an exchange which resides in a wire center, which may house several such exchanges.
- 3448 indicates the port and circuit ID, which is associated with a local loop, which, in turn, is associated with terminal equipment at The Context Corporation.
Through such a series of dialing steps, the logical address of The Context Corporation is translated, in steps, by the network in order to route the call to the intended party. Changes in the dialing scheme require changes in switch logic (COs and PABXs) in order that the switches can recognize the dialing pattern to be legitimate. The Context Corporation also has an 800 number, which the network translates into 360.336.3448 in order to route domestic calls on a toll-free basis.
Demand for telephone numbers has increased over the past few years as a result of the popularity of cellular telephones, fax machines, pagers and computer modems for access to the Internet-all of which require telephone numbers. As a result, the NPA has come under extreme pressure in the United States and internationally; hence the expansion of the international NPA dialing convention and the addition of 640 new area codes approved by the FCC in 1995 for use in the United States. The FCC currently expects another 88 existing area codes to be exhausted within the next ten years [6-4], [6-5], [6-6], [6-7], [6-8], [6-9], and [6-10]. The changes in the NPA have impacted the network to a considerable extent, as all network switches must be reprogrammed to recognize and honor dialing instructions under the new conventions.
In order to understand the implications of NPA changes, the difference between the old and new conventions must be understood. Traditionally, a U.S. area code was a three-digit, NNX number. In other words, the first and second digits were limited, while the third digit was not. Specifically, the first digit could be any number other than 1 or 0. Use of a 1 or 0 would confuse the network, which would interpret it as an instruction to provide access to an operator, connect a call across an area code boundary, or connect an international call. The second digit was required to be a 1 or 0, and the third digit could be any number. As the existing area codes were exhausted, the FCC opened the second position. Hence, The Context Corporation found itself removed from the Seattle 206 area code and established in the new 360 area code. For callers to reach the company, it was necessary that all involved switching devices be reprogrammed to recognize the validity of the new area code; thereby being able to process the call, rather than reject it. As a result, end users were required to make software changes in their CPE (PBX systems); the carriers also had to make software changes to all network switches. Not only were such software enhancements expensive, but some older switches could not be upgraded, thereby either denying access to the new number or requiring system replacements or peripheral equipment to be added to effect compatibility. The addition of 888 numbers to the In-WATS dialing convention will cause similar difficulties, as well as confusion for callers.
Domains
Perhaps the most effective initial means of examining the network is to consider the concept of domains, or spheres of influence. Specifically, the traditional voice network can be examined in terms of functional, regulatory, and carrier domains.
Functional Domains
Functional domains address the various functions performed in the PSTN. Customer premise equipment, switches, and transmission facilities all are physical elements of the PSTN, each performing specific functions, and all supported by a signaling and control system. At a higher level, the PSTN can be viewed in terms of its providing the functions of network access, transport, and service delivery.
Customer Premise Equipment (CPE)
CPE is the term used for send and receive equipment in the voice world. CPE generally is owned by the user, rather than rented from the telephone company, as was the case until the late 1960s. CPE includes voice terminals (telephone sets), key equipment, and PABXs.
Inside Wire and Cable
This includes all wires and cables inside the customer premise. Such wires and cables extend from the terminal equipment to the common equipment, such as a PBX or a Key Service Unit (KSU) in a Key System environment. Inside wire and cable extends to the demarcation point (demarc), which is the point of delineation between the customer premise and the carrier network.
- Antarnisti.com : Internet Marketing, Promotion and Brand Building Specialist
- Makassar Today : Everything You Need To Know About Insurances, Credits and Loans
- Masterbiznet.com : Masternya Bisnis Internet
- CKnol.com : The Center of Knowledges