The circuit-switched network gets organized

As circuit-switched networks continued to evolve, other technologies were developed that  helped the carriers manage their  telephony operations. Carriers began  offering more  types of POTS access and POTS carrier services.

The early  forms of local and  long-distance carrier services had  to be rede- fined according to where the  carrier company had  facilities to terminate the  circuits and  transport lines,  as well as where they  might  install their facilities. In addition, government regulation of telecommunications picked up. The concept of a local access and transport area, or LATA, as a geographical desig- nation was defined. Eventually, the  entire map  of the United  States would  be developed into thousands of LATAs. You can usually identify a particular
LATA by the  area  code associated with a telephone number.

The big advance with LATA was that it helped carriers get organized in a manner that would  let them offer other types of carrier services, including those outside the  circuit-switched services of the  PSTN. For example, a num- bering plan  was developed that identified any circuit or access transport by its area  code and  the  prefix of the  main telephone number. The area  code became known  as the  NPA, for numbering plan area,  and  the  prefix became known  as the  NXX, for number exchange. For example, the  NPA-NXX 412-882 is the  area  code and  prefix for the Pittsburgh 412 LATA and  switch 882, located in the  South Hills of the Pittsburgh 412 LATA.
What does the  NPA-NXX number have  to do with VoIP? In Chapter 7, I discuss dedicated networks that have  proven to be the  highest quality of service (QoS) network type  for VoIP networks. All carrier lines  for a dedicated VoIP network are priced using  the  NPA-NXX of each location included in the  network.

Following  the  development of digital  services, the  corporate sector began demanding more  bandwidth from carriers to support their networks. It didn’t  take  long for carrier companies to develop digital,  high-bandwidth transport lines  that could meet the  diverse needs of the  corporate sector.

These newer transport lines  would  be digital  all the  way from a customer’s location A to the  same customer’s location B, regardless of how many  miles were in between. These customer demands led to the development of trans- port services that multiplied exponentially the amount of available digital  bandwidth that could be offered  to the corporate sector.

These newer ultrahigh-bandwidth transports were not  the  same kinds  of wires  as those in the  POTS network. They  were usually a thicker-gauge wire or fiber-optic cables. When installed, they  connected two or more locations of a customer’s company in a point-to-point fashion versus the circuit-  switched method of the  PSTN.

These developments contributed to the  emergence of private dedicated net- works, which in turn ensured that VoIP would  be here  to stay. (As you find out  in later chapters, VoIP becomes a viable  option for companies only when  used over  dedicated networks.) Eventually, on-net VoIP over  dedicated net- works  will replace expensive circuit-switched calling  over  the  PSTN.