| |
Telephony and Telegraphy
Telephony is the technology of transmitting speech over a distance by converting sound into electrical signals and back again. A telephone contains a microphone that turns the speaker's voice into a varying electrical signal and an earpiece that reconverts a received signal into sound. The traditional telephone line carries this signal and supplies power from the exchange, so that basic telephones can operate even during a local power failure. Telegraphy, the earlier technology, transmitted coded messages such as Morse code rather than voice.
Connecting calls requires signalling between the telephone and the exchange. To request a call, the telephone goes off-hook and receives a dial tone indicating the exchange is ready. The number is then sent, historically by pulse dialling and later by dual-tone multi-frequency (DTMF) signalling, in which each digit is represented by a unique pair of audible tones. The exchange interprets these signals, routes the call across the network and applies a ringing current to alert the called party. A private branch exchange (PBX) provides similar switching within an organisation.
The behaviour of a telephone network under load is studied through traffic theory, which uses the erlang as a unit of traffic intensity to describe how busy circuits are and how many lines are needed to keep the probability of blocking acceptably low. The familiar tones and signals heard on a line, such as dial tone, ringing tone and busy tone, are standardised so that callers can recognise the state of a call.
Frequently asked questions
- What is DTMF dialling?
- Dual-tone multi-frequency dialling represents each key as a unique pair of audible tones, which the exchange decodes to determine the dialled digit.
- How does a telephone alert the called party?
- The exchange applies a ringing current to the called line, which operates the ringer or generates an alerting tone in the telephone.
- What is an erlang?
- It is a unit of telephone traffic intensity used to describe how heavily circuits are used and to size the number of lines a network needs.
|
|
Telephony
overview 
related topic:
Digital audio,
GSM, Modems,
VoIP - internet,
Speech technology,
Telephone
technology circuits |
|
Alexander
Graham Bell's path to the telephone |
|
Basic Telephones
The Transmitter and Receiver, The EE-8 Telephone, The Switchboard |
| Caller ID FAQ
the service provided by many telephone companies that allows one to see the number of the person who is ringing you |
|
Caractéristiques d'une ligne téléphonique en Français |
|
Cordless phone frequencies
old 10 channel cordless phone frequencies, 46/49MHz Cordless Phone frequencies,
900MHz Cordless Phone Frequencies, 2.4GHz Cordless Phone Frequencies |
|
Cordless phone frequencies
Cordless phone frequencies, Cordless Phone Information |
|
Cordless
Telephone Frequencies 46MHz Cordless Phone Frequencies, 900 MHz Cordless
Phones |
|
Cordless
Telephone Frequencies 30MHz Cordless Phone Frequencies, 46MHz Cordless Phone
Frequencies, 900 MHz Cordless Phones |
|
Cyclopedia of
Telephony & Telegraphy |
|
Home phone wiring Add a Jack, Wire 2nd Line, Wire DSL, Wire Colors, Wiring
Block Techniques and Tips, Safety Cautions, Color Codes, Network Interface,
Jacks/Adapters, 2 Line Jacks, Cable Routing, Tools, DSL Splitter, DSL Splitter
at the Router, DSL Splitter and Alarm Systems |
|
How cordless
phone works How cordless phone works, A cordless telephone or portable telephone is a telephone with a
wireless handset which communicates with a base station connected to a fixed
telephone landline (POTS) via radio waves and can only be operated close to
(typically less than 100 meters of) its base station, such as in and around the
house, ... |
|
ISDN ISDN is an
abbreviation for Integrated Services Digital Network |
|
ISDN
Access Interfaces, ISDN Reference Configurations, Your house's network (S/T
reference points), Talking to the phone company (U reference point), Signaling,
Switching, Bearer Services, Rate Adaption, Inverse Multiplexing |
| ISDN tutorial
ISDN, which stands for Integrated Services Digital Network, is a system of digital phone connections which has been
available for over a decade. This system allows voice and data to be transmitted simultaneously across the world using end-to-end digital connectivity |
|
Phone dialing pulse, loop disconnect, or rotary, Dual Tone Multi-Frequency (DTMF) or Multi-Frequency (MF) in Europe. In the U.S. MF means single tones used
for system control |
| Radio interference to
telephones |
|
Rotary dial Rotary dial system, The rotary dial is a device mounted on or in
a telephone or switchboard that is designed to send interrupted electrical
pulses, known as pulse dialing, corresponding to the number dialed, ...,
Educypedia |
|
Signals and Circuit Conditions of USA and Canadian Telephone Systems |
|
Telephone how
telephone works |
|
Telephone
Basic Telephone System, Telephone Dialing System, Polytonic Tone Sweep |
|
Telephone pulse dialing, DTMF dialing,
part of Telecom corner |
|
Telephone en Français, pdf file |
|
Telephone exchanges |
| Telephone: how it works when you pick up the phone, the switch senses the completion of your loop and it plays a dial tone sound so you know the switch and your
phone is working. The dial tone sound is simply a combination of 350 hertz tone and a 440 hertz tone, busy signal, ringing current |
|
Telephone line audio interface circuits How telephone works, Network
Interface in telephone, Telecom hybrid circuits for other equipments than
telephones, Audio interfaces to telephone lines, ... |
| Telephone
plug types by country |
| Telephone phone
wiring conventions in the United States, Pin-outs for telephone wiring |
|
Telephone
System ppt file |
|
The Splitter in
DSL Applications The Splitter in DSL Applications, pdf file |
|
Timeline of
Telecommunications |
|
Transatlantic telephone cable A transatlantic telephone cable is a submarine
communications cable that carries telephone traffic under the Atlantic Ocean
between North America and Europe, ... |
|
UK telephone wiring |
|
Understanding telephones The phone line, The speech network, The Dial,
pulse, loop disconnect, or rotary, DTMF dials, The ringing cadence |
| Why is the keypad
arrangement different for a telephone and a calculator |
| World telephone guide |
| |
|
Switching Networks |
|
ATM SWITCHING OPERATIONS
The purpose of this document is to provide an overview of the ATM technology and
to describe its switching functions, architecture, and techniques,
pdf file |
|
|
|
Telephone circuits |
| go to Telephone
technology circuits |
|
|
Home
|
Site Map
|
Email: support[at]karadimov.info
Last updated on:
2026-06-24
|
Copyright © 2011-2021 Educypedia.
https://educypedia.org
|
| |
|
|
