Telephony is the field of technology involving the development, application, and deployment
of telecommunication services for the purpose of electronic transmission of voice, fax,
or data, between distant parties. The history of telephony is intimately linked to the invention
and development of the telephone. Telephony is commonly referred to as the construction
or operation of telephones and telephonic systems and as a system of telecommunications
in which telephonic equipment is employed in the transmission of speech or other sound
between points, with or without the use of wires. The term is also used frequently to
refer to computer hardware, software, and computer network systems, that perform functions
traditionally performed by telephone equipment. In this context the technology is specifically
referred to as Internet telephony, or voice over Internet Protocol.
Overview The first telephones were connected directly
in pairs. Each user had a separate telephone wired to the locations he might wish to reach.
This quickly became inconvenient and unmanageable when people wanted to communicate with more
than a few people. The inventions of the telephone exchange provided the solution for establishing
telephone connections with any other telephone in service in the local area. Each telephone
was connected to the exchange via one wire pair, the local loop. Nearby exchanges in
other service areas were connected with trunk lines and long distance service could be established
by relaying the calls through multiple exchanges. In modern times, most telephones are plugged
into telephone jacks. The jacks are connected by inside wiring to a drop wire which connects
the building to a cable. Cables usually bring a large number of drop wires from all over
a district access network to one wire center or telephone exchange. When a telephone user
wants to make a telephone call, equipment at the exchange examines the dialed telephone
number and connects that telephone line to another in the same wire center, or to a trunk
to a distant exchange. Most of the exchanges in the world are interconnected through a
system of larger switching systems, forming the public switched telephone network.
After the middle of the 20th century, fax and data became important secondary users
of the network created to carry voices, and late in the century, parts of the network
were upgraded with ISDN and DSL to improve handling of such traffic.
Today, telephony uses digital technology in the provisioning of telephone services and
systems. Telephone calls can be provided digitally, but may be restricted to cases in which the
last mile is digital, or where the conversion between digital and analog signals takes place
inside the telephone. This advancement has reduced costs in communication, and improved
the quality of voice services. The first implementation of this was that permitted all data transport
from end-to-end speedily over telephone lines. This service was later made much less important
due to the ability to provide digital services based on the IP protocol.
Since the advent of personal computer technology in the 1980s, computer telephony integration
has progressively provided more sophisticated telephony services, initiated and controlled
by the computer, such as making and receiving voice, fax, and data calls with telephone
directory services and caller identification. The integration of telephony software and
computer systems is a major development in the evolution of the automated office. The
term is used in describing the computerized services of call centers, such as those that
direct your phone call to the right department at a business you're calling. It's also sometimes
used to describe the ability to use your personal computer to initiate and manage phone calls.
CTI is not a new concept and has been used in the past in large telephone networks, but
only dedicated call centers could justify the costs of the required equipment installation.
Primary telephone service providers are offering information services such as automatic number
identification, which is a telephone service architecture that separates CTI services from
call switching and will make it easier to add new services. Dialed Number Identification
Service on a scale is wide enough for its implementation to bring real value to business
or residential telephone usage. A new generation of applications is being developed as a result
of standardization and availability of low cost computer telephony links.
Recent developments The term's scope has been broadened with the
advent of the different new communication technologies. In its broadest sense, the terms
encompasses phone communication, Internet calling, mobile communication, faxing, voicemail
and video conferencing. Telephony's initial idea returns to POTS, technically called the
PSTN. This system is being fiercely challenged by
and to a great extent yielding to Voice over IP technology, which is also commonly referred
to as IP Telephony and Internet Telephony. IP telephony is a modern form of telephony
which uses the TCP/IP protocol popularized by the Internet to transmit digitized voice
data. Also, unlike traditional phone service, IP telephony service is relatively unregulated
by government. In the United States, the Federal Communications Commission regulates phone-to-phone
connections, but says they do not plan to regulate connections between a phone user
and an IP telephony service provider.Using the Internet, calls travel as packets of data
on shared lines, avoiding the tolls of the PSTN. The challenge in IP telephony is to
deliver the voice, fax, or video packets in a dependable flow to the user. Much of IP
telephony focuses on that challenge. Digital telephony
Starting with the introduction of the transistor, invented in 1947 by Bell Laboratories, to
amplification and switching circuits in the 1950s, and through development of computer-based
electronic switching systems, the public switched telephone network has gradually evolved towards
automation and digitization of signaling and audio transmissions.
Digital telephony is the use of digital electronics in the operation and provisioning of telephony
systems and services. Since the 1960s a digital core network has replaced the traditional
analog transmission and signaling systems, and much of the access network has also been
digitized. Digital telephony has dramatically improved
the capacity, quality, and cost of the network. End-to-end analog telephone networks were
first modified in the early 1960s by upgrading transmission networks with Digital Signal
1 carrier systems, designed to support the basic 3 kHz voice channel by sampling the
bandwidth-limited analog voice signal and encoding using PCM. While digitization allows
wideband voice on the same channel, the improved quality of a wider analog voice channel did
not find a large market in the PSTN. Later transmission methods such as SONET and
fiber optic transmission further advanced digital transmission. Although analog carrier
systems existed that multiplexed multiple analog voice channels onto a single transmission
medium, digital transmission allowed lower cost and more channels multiplexed on the
transmission medium. Today the end instrument often remains analog but the analog signals
are typically converted to digital signals at the serving area interface, central office,
or other aggregation point. Digital loop carriers place the digital network ever closer to the
customer premises, relegating the analog local loop to legacy status.
Milestones in digital telephony early experiments with pulse code modulation
in telephony the 8-bit, 8 kHz standard is developed; Nyquist's
theorem and the standard 3.5 kHz telephony bandwidth
DS0 as the basic digital telephony bitstream standard
non-linear quantization: A-law vs. μ-law, and transcoding between the two
bit error rate and intelligibility first practical digital telephone systems
put into service the U.S. T-carrier system and the European
E-carrier system developed to carry digital telephony
introduction of space-time switching in fully digital electronic switching systems
replacement of tone signaling with digital signaling for trunks
in-band signaling vs. out-of-band signaling the problem of bit-robbing
development of SS7 emergence of fiber optic networking allows
greater reliability and call capacity transition from plesiochronous transmission
to synchronous systems like SONET/SDH optical self-healing ring networks further
increase reliability digital/optical systems revolutionize international
long-distance networks, particularly undersea cables
digital telephone exchanges eliminate moving parts, make exchange equipment much smaller
and more reliable separation of exchange and concentrator functions
roll-out of digital systems throughout the PSTN
provision of intelligent network services digital speech coding and compression
speech compression on international digital trunks
phone tapping in the digital environment introduction of digital mobile telephony,
specialized compression algorithms for high bit error rates
direct digital termination to customers via ISDN; PRI catches on, BRI mostly does not,
except in Germany the effects of digital telephony, and digital
termination at the ISP, on modem performance voice over IP as a carrier strategy
emergence of ADSL leads to voice over IP becoming a consumer product, and the slow demise of
dial-up Internet access expected convergence of VoIP, mobile telephony,
etc. flattening of telephony tariffs, increasing
moves towards flat rate pricing as the marginal cost of telephony drops further and further.
IP telephony
A specialization of digital telephony, Internet Protocol telephony involves the application
of digital networking technology that were the foundation to the Internet to create,
transmit, and receive telecommunications sessions over computer networks. Internet telephony
is commonly known as voice over Internet Protocol, reflecting the principle, but it has been
referred with many other terms. VoIP has proven to be a disruptive technology that is rapidly
replacing traditional telephone infrastructure technologies. As of January 2005, up to 10%
of telephone subscribers in Japan and South Korea have switched to this digital telephone
service. A January 2005 Newsweek article suggested that Internet telephony may be "the next big
thing." As of 2006 many VoIP companies offer service to consumers and businesses.
IP telephony uses an Internet connection and hardware IP Phones, analog telephone adapters,
or softphone computer applications to transmit conversations encoded as data packets. In
addition to replacing plain old telephone service, IP telephony services are also competing
with mobile phone services by offering free or lower cost connections via WiFi hotspots.
VoIP is also used on private networks which may or may not have a connection to the global
telephone network.
Social impact research Direct person-to-person communication includes
non-verbal cues expressed in facial and other bodily articulation, that cannot be transmitted
in traditional voice telephony. Video telephony restores such interactions to varying degrees.
Social Context Cues Theory is a model to measure the success of different types of communication
in maintaining the non-verbal cues present in face-to-face interactions. The research
examines many different cues, such as the physical context, different facial expressions,
body movements, tone of voice, touch and smell. Various communication cues are lost with the
usage of the telephone. The communicating parties are not able to identify the body
movements, and lack touch and smell. Although this diminished ability to identify social
cues is well known, Wiesenfeld, Raghuram, and Garud point out that there is a value
and efficiency to the type of communication for different tasks. They examine work places
in which different types of communication, such as the telephone, are more useful than
face-to-face interaction. The expansion of communication to mobile telephone
service has created a different filter of the social cues than the land-line telephone.
The use of instant messaging, such as texting, on mobile telephones has created a sense of
community. In The Social Construction of Mobile Telephony it is suggested that each phone
call and text message is more than an attempt to converse. Instead, it is a gesture which
maintains the social network between family and friends. Although there is a loss of certain
social cues through telephones, mobile phones bring new forms of expression of different
cues that are understood by different audiences. New language additives attempt to compensate
for the inherent lack of non-physical interaction. See also
List of telephony terminology History of the telephone
Invention of the telephone References