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Circuit Switching and Packet Switching
Published in Vikas Kumar Jha, Bishwajeet Pandey, Ciro Rodriguez Rodriguez, Network Evolution and Applications, 2023
Vikas Kumar Jha, Bishwajeet Pandey, Ciro Rodriguez Rodriguez
Common battery service is mostly provided by the urban exchanges, where the central office has to provide the power for operation of the transmitter and automatic dials signaling to the subscriber telephone circuits. The wires used to connect subscriber’s telephone with the exchange contain a nominal 48V DC potential across the conductors from the telephone service provider end in a common battery system. The circuit connection of a telephone system is such that it represents an open circuit when the telephone is on-hook or idle. The moment a subscriber’s phone is off-hook or removed from its idle position, the circuit connection of the telephone system faces an electrical resistance across the line causing the current to flow through the wires connecting the telephone toward the central office. This current flows through a relay coil in a manually operated switchboard and actuates a buzzer or a lamp on the operator’s switchboard to signal the operator for switching action.
Distribution of audio signals
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2013
David M. Davidson, Bev Marks, Francis Rumsey
To set up a connection through the network from one telephone to the other there must be a means of identifying individual telephone lines: the directory number. Thus every telephone throughout the world must have a unique number. From the directory number of the calling and the called number it must be possible for the exchange equipment to determine a route for the call via the network of telephone exchanges. When a caller lifts the handset this action signals to the exchange that the caller wishes to set up a call. The exchange signals to the caller that it is ready to receive instructions by returning the dial tone. The caller signals the desired destination telephone by dialling the directory number of the distant telephone. The exchange then decodes this directory number and translates it into routing information to set the connection up through the switches within the exchange or exchanges. When the distant telephone�s status has been determined, i.e. busy or free, this is signalled back to the caller. If the distant party is free the equipment will apply a ringing signal to the called telephone to alert the telephone. When the called telephone handset is taken off the hook this signals to the exchange that the call has been answered and the ringing should be removed from the line, the line placed into the busy state as far as other callers are concerned and the call connection established for end-to-end voice communication. When the caller or the called party concludes the conversation, either will replace the telephone handset and this will signal to the exchange that the call has terminated and the equipment used in setting up the call should be released and both telephone lines returned to the idle condition to await the next call.
Digital Switching Systems
Published in Goff Hill, The Cable and Telecommunications Professionals' Reference, 2012
To indicate calling and clearing conditions, a contact is provided to interrupt the line current. This contact is open in the idle state and closes (makes) when a call is originated or answered. Because in many instruments it is operated by the weight of the handset, it is known as the gravity switch. But in much modern equipment, it is operated by a push button on the handset or terminal. It is also known as a “switch hook” contact and the terms “off-hook” and “on-hook” are often used to describe signaling conditions corresponding to the contact closed or open, respectively.
Concurrent Solar-Illumination and Power Line Voice Communication for Indian Underground Coal Mines – An Experimental Study
Published in IETE Journal of Research, 2022
R. N. Raul, T. Maity, S. Palit
The load end voltages in case of both the modes indicate the voltage drops in the circuits. The impedance of a telephone, when off-hook, will drop the voltage from supply to the recorded level across the telephone line. In the experimental model two telephone sets are considered to fulfil the minimum number required to establish any voice communication. These sets may be placed at two end locations in the system. Initially there is no current through the communication path. A small current of around 0.04 A flows through during the working of telephone sets in talking state. This results in a small hike in the line current as compared to the idle state, which marginally increases the power consumption as well.