In telecommunication, telephony encompasses the general use of equipment to provide voice communication over distances, specifically by connecting telephones to each other. Telephones originally were connected directly together in pairs. Each user had separate telephones wired to the various places he might wish to reach. This became inconvenient when people wanted to talk to many other telephones, so the telephone exchange was invented. Each telephone could then be connected to other local ones, thus inventing the local loop and the telephone call. Soon, nearby exchanges were connected together by trunk lines, and eventually far away ones were.

Outside Influences
Agencies like the FCC help regulate and standardize the telephone industry. For example: The FCC has adopted detailed “slamming” rules to prevent telephone companies from switching subscribers from one preferred telephone company to another without authorization.

Public Switched Telephone Network
The public switched telephone network (PSTN) is the network of the world's public circuit-switched telephone networks, in much the same way that the Internet is the network of the world's public IP-based packet-switched networks. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital, and now includes mobile as well as fixed telephones.

The PSTN was the earliest example of traffic engineering to deliver Quality of Service (QoS) guarantees. A.K. Erlang (1878–1929) is credited with establishing the mathematical foundations of methods required to determine the amount and configuration of equipment and the number of personnel required to deliver a specific level of service.

In the 1970s the telecommunications industry conceived that digital services would follow much the same pattern as voice services, and conceived a vision of end-to-end circuit switched services, known as the Broadband Integrated Services Digital Network (B-ISDN). The B-ISDN vision has been overtaken by the disruptive technology of the Internet. Only the oldest parts of the telephone network still use analog technology for anything other than the last mile loop to the end user, and in recent years digital services have been increasingly rolled out to end users using services such as DSL, ISDN, FTTP and cable modem systems.

Many observers believe that the long term future of the PSTN is to be just one application of the Internet - however, the Internet has some way to go before this transition can be made. The QoS guarantee is one aspect that needs to be improved in the Voice over IP (VoIP) technology.

There are a number of large private telephone networks which are not linked to the PSTN, usually for military purposes. There are also private networks run by large companies which are linked to the PSTN only through limited gateways, like a large private branch exchange (PBX).

The PSTN is largely governed by technical standards created by the ITU-T, and uses E.163/E.164 addresses (known more commonly as telephone numbers) for addressing.

Central Office
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls. A central office is the physical building used to house inside plant equipment including telephone switches, which make phone calls "work" in the sense of making connections and relaying the speech information.

The term exchange can also be used to refer to an area served by a particular switch (typically known as a wire center in the US telecommunications industry). More narrowly, in some areas it can refer to the first three digits of the local number. In the three-digit sense of the word, other obsolete Bell System terms include office code and NXX. In the United States, the word exchange can also have the legal meaning of a local access and transport area under the Modification of Final Judgment (MFJ).

Local Loop
In telephony, the local loop (also referred to as a subscriber line) is the physical link or circuit, that connects from the demarcation point of the customer premises to the edge of the carrier, or telecommunications service provider, network. At the edge of the carrier network in a traditional PSTN (Public Switched Telephone Network) scenario, the local loop terminates in a circuit switch housed in an ILEC (Incumbent Local Exchange Carrier) CO (Central Office). Traditionally, the local loop was wireline in nature from customer to central office, specifically in the form of an electrical circuit (i.e., loop) provisioned as a single twisted pair in support of voice communications. However, modern implementations may include a digital loop carrier system segment or fiber optic transmission system known as fiber-in-the-loop.

The local loop may terminate at a circuit switch owned by a CLEC (Competitive LEC) and housed in a POP, which typically is either an ILEC CO or a "carrier hotel".

A local loop may be provisioned to support data communications applications, or combined voice and data such as digital subscriber line (DSL).

Local loop connections can be used to carry a range of services, including:

• Analog voice and signaling used in traditional POTS
• Integrated Services Digital Network (ISDN)
• Variants of Digital Subscriber Line (DSL)

Many owners of local loops are public utilities that hold a natural monopoly. To prevent the owner from using this natural monopoly to monopolize other fields of trade, some jurisdictions require utilities to unbundle the local loop, that is, make the local loop available to their competitors.

The term "local loop" is sometimes used for any "last mile" connection to the customer, regardless of technology or intended purpose. Hence the phrase "wireless local loop".

Internet Engineering Task Force
The Internet Engineering Task Force (IETF) is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual. The IETF Mission Statement is documented in RFC 3935.

The actual technical work of the IETF is done in its working groups, which are organized by topic into several areas (e.g., routing, transport, security, etc.). Much of the work is handled via mailing lists. The IETF holds meetings three times per year.

The Internet Engineering Task Force (IETF) develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standard bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite. It is an open standards organization, with no formal membership or membership requirements. All participants and leaders are volunteers, though their work is usually funded by their employers or sponsors; for instance, the current chairperson is funded by VeriSign and the U.S. government's National Security Agency.

It is organized into a large number of working groups and informal discussion groups (BoF)s, each dealing with a specific topic. Each group is intended to complete work on that topic and then shut down. Each working group has an appointed chair (or sometimes several co-chairs), along with a charter that describes its focus, and what and when it is expected to produce.

References
The Internet Engineering Task Force http://www.ietf.org/

WikiPedia http://en.wikipedia.org/wiki/Main_Page