A telephone call is a connection over a telephone network between the called party and the calling party.
Video Telephone call
First telephone call
The first telephone call was made on March 10, 1876 by Alexander Graham Bell. Bell demonstrated his ability to "talk with electricity" by transmitting a call to his assistant, Thomas Watson. The first words transmitted were "Mr Watson, come here. I want to see you."
This event has been called Bell's "greatest success", as it demonstrated the first successful use of the telephone. Although it was his greatest success, he refused to have one in his own home because it was something he invented by mistake and saw it as a distraction from his main studies.
Maps Telephone call
Information transmission
A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile transmission when they are using fax machines. The call may use land line, mobile phone, satellite phone or any combination thereof. When a telephone call has more than one called party it is referred to as a conference call. When two or more users of the network are sharing the same physical line, it is called a party line or Rural phone line.
If the caller's wireline phone is connected directly to the calling party, when the caller takes their telephone off-hook, the calling party's phone will ring. This is called a hot line or ringdown. Otherwise, the calling party is usually given a tone to indicate they should begin dialing the desired number. In some (now very rare) cases, if the calling party cannot dial calls directly, they will be connected to an operator who places the call for them.
Calls may be placed through a public network (such as the Public Switched Telephone Network) provided by a commercial telephone company or a private network called a PBX. In most cases a private network is connected to the public network in order to allow PBX users to dial the outside world. Incoming calls to a private network arrive at the PBX in two ways: either directly to a users phone using a DDI number or indirectly via a receptionist who will answer the call first and then manually put the caller through to the desired user on the PBX.
Most telephone calls through the PSTN are set up using ISUP signalling messages or one of its variants between telephone exchanges to establish the end to end connection. Calls through PBX networks are set up using QSIG, DPNSS or variants.
Costs
Some types of calls are not charged, such as local calls (and internal calls) dialed directly by a telephone subscriber in Canada, the United States, Hong Kong, United Kingdom, Ireland or New Zealand (Residential subscribers only). In most other areas, all telephone calls are charged a fee for the connection. Fees depend on the provider of the service, the type of service being used (a call placed from a landline or wired telephone will have one rate, and a call placed from a mobile telephone will have a different rate) and the distance between the calling and the called parties. In most circumstances, the calling party pays this fee. However, in some circumstances such as a reverse charge or collect call, the called party pays the cost of the call. In some circumstances, the caller pays a flat rate charge for the telephone connection and does not pay any additional charge for all calls made. Telecommunication liberalization has been established in several countries to allows customers to keep their local phone provider and use an alternate provider for a certain call in order to save money.
Placing a call
A typical phone call using a traditional phone is placed by picking the phone handset up off the base and holding the handset so that the hearing end is next to the user's ear and the speaking end is within range of the mouth. The caller then rotary dials or presses buttons for the phone number needed to complete the call, and the call is routed to the phone which has that number. The second phone makes a ringing noise to alert its owner, while the user of the first phone hears a ringing noise in its earpiece. If the second phone is picked up, then the operators of the two units are able to talk to one another through them. If the phone is not picked up, the operator of the first phone continues to hear a ringing noise until they hang up their own phone.
One of the main struggles for Alexander Graham Bell and his team was to prove to non-English speakers that this new phenomenon "worked in their language." It was a concept that was hard for people to understand at first.
In addition to the traditional method of placing a telephone call, new technologies allow different methods for initiating a telephone call, such as voice dialing. Voice over IP technology allows calls to be made through a PC, using a service like Skype. Other services, such as toll-free dial-around enable callers to initiate a telephone call through a third party without exchanging phone numbers. Originally, no phone calls could be made without first talking to the Switchboard operator. Using 21st century mobile phones does not require the use of an operator to complete a phone call.
The use of headsets is becoming more common for placing or receiving a call. Headsets can either come with a cord or be wireless.
A special number can be dialed for operator assistance, which may be different for local vs. long-distance or international calls.
Tones
Preceding, during, and after a traditional telephone call is placed, certain tones signify the progress and status of the telephone call:
- a dial tone signifying that the system is ready to accept a telephone number and connect the call
- either:
- a ringing tone signifying that the called party has yet to answer the telephone
- a busy signal (or engaged tone) signifying that the called party's telephone is being used in a telephone call to another person (or is "off the hook" though no number has been dialled, i.e. the customer does not want to be disturbed)
- a fast busy signal (also called reorder tone or overflow busy tone) signifying that there is congestion in the telephone network, or possibly that the calling subscriber has delayed too long in dialling all the necessary digits. The fast busy signal is generally twice as fast as the normal busy signal.
- status tones such as STD notification tones (to inform the caller that the telephone call is being trunk dialled at a greater cost to the calling party), minute minder beeps (to inform the caller of the relative duration of the telephone call on calls that are charged on a time basis), and others
- a tone (sometimes the busy signal, often the dial tone) to signify that the called party has hung up.
- tones used by earlier inband telephone switching systems were simulated by a Red box or a blue box used by "phone phreaks" to illegally make or receive free trunk/toll calls.
- off-hook tone if the phone has been picked up but no number dialed for an extended period of time.
Cell phones generally do not use dial tones, because the technology used to transmit the dialed number is different from a landline.
Unwanted calls
Unsolicited telephone calls are a modern nuisance. Common kinds of unwanted calls include prank calls, telemarketing calls, and obscene phone calls.
Caller ID provides some protection against unwanted calls, but can still be turned off by the calling party. Even where end-user Caller ID is not available, calls are still logged, both in billing records at the originating telco and via automatic number identification, so the perpetrator's phone number can still be discovered in many cases. However, this does not provide complete protection: harassers can use payphones, in some cases, automatic number identification itself can be spoofed or blocked, and mobile telephone abusers can (at some cost) use "throwaway" phones or SIMs.
Patents
- Rabinow, J., U.S. Patent 2,813,154 -- "Telephone call indicator"--November 12, 1957
See also
- Call completion
- Call processing
- Emergency telephone number
- Pocket dialing
- Telephone phobia
- Teletraffic engineering
References
Source of the article : Wikipedia
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