Telephone Call

A telephone call is a connection over a telephone network between the calling party and the called party.

Information transmission
A telephone call may consist of an ordinary voice transmission using a telephone, a data transmission when the calling party and called party are using modems, or a facsimile transmission when the two parties are using fax machines. Where a telephone call has more than one called party it is referred to as a conference call.

Calls are usually placed through a network (such as the Public Switched Telephone Network) provided by a commercial telephone company. If the caller's wireline phone is directly connected 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, the calling party cannot dial calls directly, and is connected to an operator who places the call for them.

Most telephone calls in the world are set up using ISUP messages or one of its variants between telephone exchanges to establish the end to end connection.


[edit] Costs
Some types of calls are not charged, such as local calls dialed directly by a telephone subscriber in Canada, the United States, Hong Kong, 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.


[edit] Tones
A typical phone call is placed by picking the phone handset up off the base and holding the handset so that the hearing end is next to the users ear and the speaking end is within range of the mouth. Headsets are becoming more and more common, especially in car headsets, thus changing the way that people are conducting telephone calls in modern times. Preceding, during, and after a telephone call is placed, certain tones signify the progress and status of the telephone call:

a dial tone signifying that the call is ready to be placed
either:
a ringing tone signifying that the calling party has yet to answer the telephone
a busy signal (or engaged tone) signifying that the calling party's telephone is being used in a telephone call to another person (or is "off the hook" though no number has been dialled, ie the customer does not want to be disturbed)
a busy signal (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
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) to signify that the called party has hung up.
tones used by earlier inband telephone switching systems were simulated by a Black box or a Blue box used by "phone phreaks" to illegally make or receive free trunk/toll calls, see Blue box.