Purchase this or other Telephone Domains
Staying Connected:
Connectivity refers to the use of computer networks to link to people and resources. A computer network is a group of interconnected computers.
Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories
and presents the basic components of a network. You can link or connect to large computers and the Internet
providing access to world-wide information resources just by sitting in front of and clicking on your computer. On a larger, collective scale
connectivity may refer to the internet bandwidth coming into and going out of a country, and the quality of the infrastructure within the country
for linking to the internet.
With respect to Global Telephone Connectivity, the Internet has taken this a whole step further with Public Telephone Networks.
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 is largely governed by technical standards created by the ITU-T, and uses E.163/E.164 addresses (more commonly known as telephone numbers)
for addressing.
Global Telephone Network Architecture and context:
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).
Early history:
The first telephones had no network but were in private use, wired together in pairs. Users who wanted to talk to different people had as many
telephones as necessary for the purpose. A user who wished to speak, whistled into the transmitter until the other party heard. Soon, however, a
bell was added for signalling, and then a switchhook, and telephones took advantage of the exchange principle already employed in telegraph networks.
Each telephone was wired to a local telephone exchange, and the exchanges were wired together with trunks. Networks were connected together in a
hierarchical manner until they spanned cities, countries, continents and oceans. This was the beginning of the PSTN, though the term was unknown for
many decades.
Automation introduced pulse dialing between the phone and the exchange, and then among exchanges, followed by more sophisticated address signaling
including multi-frequency, culminating in the SS7 network that connected most exchanges by the end of the 20th century.
