How A Phone Call Works: Then And Now

HOW A PHONE CALL WORKS: THEN AND NOW A lot has changed since Alexander Graham Bell's historic first phone call-to his assistant, in the next room-on March 10, 1876. We think he'd be proud of how his little invention took off. Here's how the process worked, from the ivory-handled "bell box" wall phones of yesteryear to today's untethered smartphones. 2 At the processing center, your incoming signal would buzz a buzzer or light a light to let the operator know you wanted to make a call. She 5 Armed with marching orders, the operator sent a low electrical pulse signal down the wire to the phone in the Smiths' house, where it activated a solenoid-a copper-wire coiled around an iron bar, inducing an alternating magnetic field that shuttled the bar back and forth between fixed 000ol00000 ... The operator kept the I connection alive and plugged in-and the Smiths kept hearing that ringing sound- until either they picked up land she would When you lifted the old-timey receiver off the tilting switch (the 'hook') to call your friends the Smiths, it completed a hard-wired circuit, sending electricity humming between your house along telephone poles in the street to the ..opoo00000000. would plug her headset's jack into your line, completing a circuit with you so you could speak to one another. 4 The operator's head- phone held speakers wired to reconvert your electrical signal back to audio waves. The connect or "tie" the bells, producing a then- familiar ringing sound, and startling the Smiths from their supper (generally pot roast). lines together and then disconnect her headset for privacy) or the operator tired of waiting and disconnected the call. waveform represent- ing "Hi Mabel.Dial up the Smiths for me, will ya?" moved through an electromagnetic coil, alternately magnetizing and demagnetizing its iron core, vibrating a speaker diaphragm so as to produce an audio wave her ear could detect and that "Number, please?" CARBON GRAINS phone company's local station's switchboard/ processing center. MAGNET DIAPHRAGM You spoke into the phone's mouthpiece (originally a separate unit, later connected to the earpiece), where a flexible diaphragm "Hi Mabel...." converted the sound corresponded to your original voice tones. 1895 "Hi Mabel..." DRY CELLS waves of your voice into an electrical signal, by moving a conductive copper coil closer to, or further from, a magnet. The resulting electrical waveform, or "signal," would travel out along the line toward the 45+ seconds to call your neighbor. operator's headset. 1 Pressing the touchscreen of your Ismartphone-a virtual "Call" button, for example, or a link representing a phone number-activates your phone's touchscreen sensor system (the mechanics vary) to create a binary string representing the relevant phone number (say, your |friend Paolo in Italy) stored in your phone's hard drive. 3 The wave moves through the air on FCC-approved frequencies in the elec- tromagnetic spectrum. (The "97.5" of your "Hot 97.5" radio station is 7 Paolo's phone (which, Iwhen on, is always pinging the nearest cell-towers looking for incoming calls) receives the signal, and activates his Justin 2014 4 The first intermediary, as Iyou place the call, is the nearest cell tower.one of Paolo that in megahertz; for cellphones the FCC has reserved frequencies in the range of 700 MHz- 2.6 GHz.) equency ador Timberlake ringtone. When he presses his some five million worldwide These towers are spaced so as to form a "grid" of hexag- onal cells, which is why your phone's called a cellphone. If you are calling from a moving train, the call may be handled by a succession of cell towers. 5 seconds to call 5 The cell tower is essentially a giant, I sophisticated antenna, which is always 'on' and monitoring approved frequencies for incoming calls. It receives your signal, decodes the intended path, and relays it (via hard- wire) to other towers and base stations. As this call's going to Italy, your signal will be sent to one of the many undersea fiber-optic cables crisscrossing the Atlantic Ocean (About 1 out of every 100 calls will be uplinked to a communications satellite-once the workhorse of touchscreen button to accept the call, the relevant towers pass the information along, keeping the two-way communication going. anyone in the world. 6 After passing through the Iundersea cable, your call is relayed to the nearest cell tower to the local phone number you're trying to call (actually, the unique ID number Paolo's telecom provider associates with his phone number). 1010101010101010 01 1101011011010101010 10101101011001010 0101101011010110110 “Buon giorno!" 2 The telephone function of your Ismartphone is best thought of as a two-way radio, with transmitters and receivers in your phone and Paolo's passing radio waves back and forth, with help from various intermediaries. The intended call's destination "number" is convert- 8 "Buon giorno!" As you I and Paulo speak at last, your phones' tiny micro- phones and speakers use microprocessors to turn audio waves into digital data streams that are then encrypted (for privacy), packetized (for efficiency), and transmitted...then reverse-processed at the other end, where tiny speakers convert the pro- cessed digital stream back into an audio wave ears can 101011011 1010 os0101010101010 0101101011 telecommunications, but much slower compared to fiber-optics). ed to an efficient binary packet, expressed as a radio wave your phone's transmitter can broadcast. “Buon giorno!" understand. ((