The Network Hierarchy (Post 1984)
After 1984 the network took a dramatic turn, with the separation of the Bell Operating Companies (BOCs) from AT&T. Many users screamed that things would fall apart, with service being affected. None of this came true, however. This doesn’t mean that there was not a lot of confusion, there certainly was. However, things just kept humming along for the most part and calls were completed through this series of interconnecting points called the network.
The hierarchy of the network introduced a new set of terms and connections. The BOCs were classified the same as independent telephone companies. They are all called local exchange carriers (LECs). The seven spin-off companies formed as a result of the divestiture became Regional Bell Holding Companies (RBHC), which had regulated arms called the Regional Bell Operating Companies (RBOC). Each RBOC had the Bell Operating Companies in its geographical area. Additionally, the RBHCs also had an unregulated side of the business, where new ventures could be entered into (such as equipment sales, finance, real estate, etc.).
Equal access, or the ability of every interexchange carrier (IEC or IXC) to connect to the Bell operating companies for long-distance service became a reality. Equal access was designed to allow the same access to other long-distance competitors that AT&T had always enjoyed prior to divestiture. Prior to divestiture, a customer attempting to use an alternative long-distance supplier would have to dial a 7- or 10-digit telephone number to get to this supplier’s switch. Then, upon completion of this connection, a computer would answer the call and place a tone on the line. From there, the caller would have to enter a 7- to 11-digit authorization code. This code identified the caller by telephone number, caller name and address, and the billing arrangements. Only after the computer (switch) verified this information would it then send dial tone to the caller’s ear. The caller would then have to dial the 10-digit telephone number of the requested party. This could involve very lengthy and frustrating call set-up times—especially when the called number was busy.
Users chose not to use these alternative carriers because of the time, the number of digits required, and the frustration of busy call attempts. That is, unless the organization forced the user to dial across the carriers’ networks. The reason for all of the digits was simple. The telephone company did not pass on the caller information to the alternate carrier (MCI, Sprint, ITT, etc.) that they did to AT&T. Thus, the choice of many callers was AT&T because it was simpler. Now the caller information is passed on in an equal basis, hence the access is equal.
However, some of the independents and BOCs who haven’t yet upgraded their offices do not connect to these IECs. These are called nonconforming end offices. The point of presence (POP) is the point where the IEC and the LEG are interconnected. This usually refers to AT&T, MCI, Sprint, and other carrier’s offices. This name is now starting to change to the point of interface (POI) as opposed to POP. The main reason is that a POP implies that a switching system is at the location, which is not always true. The point of interface is where the two parties, Bell or independent, and the carrier connect. This can be a closet in a basement or hotel, connected to a dedicated trunk to another part of the country. All of this should be transparent to the end user, however.
This introduction is meant to teach you about the functions and technology of a Central Office.
Analog to Digital Bandwidth
The Telephone Network
A Topology of Connection
Network Hierarchy (pre 1984)
Network Hierarchy (post 1984)
North American Numbering Plan
The Subscriber Extension
Local Access and Transport Areas
Wiring Connections: Hooking Things Up
Types of Communication
Lines Vs. Trunks
Foreign Exchange Signal