4.1. Regulation and Organization of the PSTN
The organization of the telephone network is a complex international affair. If you're dealing with telephony of anything deeper than a superficial level, you need to understand the players.
4.1.1. The FCC
In the United States, the public telephone system falls under each state's regulatory jurisdiction. This means that, while the FCC sets the rules for interstate service, it's up to the individual states' communications agencies to enforce and further define local service standards for the PSTN (see Figure 4-1).
Figure 4-1. There are several kinds of network carriers on the PSTN
The FCC communicates with these bodies in order to make sure that the PSTN serves the public interest and is beneficial to consumers, while allowing an atmosphere of economic growth that is conducive to the involvement of private business. Though the PSTN's technologies are governed by the ITU, an international body, state governments and the FCC maintain lawful use of the PSTN in the U.S.A.
4.1.2. The International Telecommunications Union
The ITU-T (Telecommunications Standardization Sector) is the ITU's working group charged with governance of global standards for telephony practices and protocols. The ITU-T publishes recommendations that dictate the technologies used in public and private telephony. While the ITU-T has published some packet-based recommendations, like H.323, the majority of its work has focused on legacy, circuit-switched telephony networking. Its standards are categorized into groups by function. Each group is abbreviated using a letter. Here are the most relevant ones:
So Q.931 is a signaling protocol recommendation, while E.164 is a recommendation for a numbering scheme used for international dialing. V.90 is a modem communication recommendation, while H.248 is a media gateway signaling standard. A library of these standards is maintained online by the ITU-T. The service providers who are most directly affected by, and who most frequently use, all of these recommendations are the companies that operate the PSTN: RBOCs, CLECs, IXCs, and LD carriers.
4.1.3. RBOCs and CLECs
Regional Bell operating companies, or RBOCs, are the largest of the local phone service providers. These are the companies that tend to own most of the cabling infrastructure in areas that are routinely as big as an entire state. They are sometimes referred to as incumbent carriers because most of them got their start as a part of a huge, national corporation called AT&T that was once in charge of the national telephone system. In the early 1980s, that company was disbanded and broken into many smaller regional Bell operating companies.
Competitive local exchange carriers, or CLECs, are local telephone companies operating competitively within each RBOC region. Unlike RBOCs, CLECs don't tend to own much cabling or switching infrastructure. Instead, they usually share facilities with the RBOCs. CLECs rose to notoriety in the late 1990s, after the Telecommunications Act of 1996 was passed by Congress, allowing regional competition for dialtone services.
RBOCs and CLECs are also referred to simply as LECs, or local exchange carriers. Both are monitored and regulated by the FCC.
220.127.116.11 LD carriers
Long-distance carriers are service providers that provide network pathways between RBOCs' and CLECs' switches in different regions known as LATAs (local access transport areas). LD carriers route telephone calls for subscribers of the local telephone companies while billing the subscribers directly or as a part of the local phone companies' billing routines. They carry voice traffic across the country and throughout the world, so that the PSTN can extend beyond its RBOC roots. Due to deregulation of the LD carrier business in the past few years , it's now possible for RBOCs and LD carriers to offer the same services, and many do.
Interexchange carriers are network operators that provide connections between PSTN network carriers. A network connection between a dedicated LD service provider and a regional Bell operating company may pass through an IXC. Many LD carriers are considered IXCs, too.
Internet service providers, though not a part of the PSTN, are often operated by the same companies that provide PSTN services. Lots of large LD carriers, RBOCs, and CLECs are ISPs, too.