    





    HO~ IT WORKS
    
    There are two basic types of telephone offices thru
    which all calls are swiLched. The first is the CO,
    or Central Office. The wires from your telephone go
    to your local CO. From there your call is switched
    to another telephone in the same CO, meaning a local
    call, or it is switched to a toll office. A toll of-
    fice, for our purposes, is an ~inter-office" office.
    The toll office connects different CO's to each'
    other.
    When you dial a call from your phone, and suppose it
    happens to be long distance, the digits ycu dial,
    whether t},ey are tauchtone or dia! type pulses, are
    sent directly to your central office. t10st CO's have
    CAMA, Certralized automatic message accalnting. The
    CAMA machire in the CO records your nuTber, the date
    and ti~e, and the number you dialed. The record is
    a purched paper tape. The CO then relays the area
    code and nu~ber to the toll office. The toll office
    contains a sender, which sends by whatever route is
    easiest a series of MF,cr multifrequency pulses to
    another toll office in the area you called. These
    are picked up by an incoming sendec, which translaces
    and connects you to the CO dialed. The C0 then itself
    translates the remaining digits and connects you to
    the lire you dialed. When tbat line answers, a signal
    is returned all the way down the line to your CO to
    say that the call is completed. The punched paper
    tspe records this. When you or your friend hang up,
    a signal is returned to end billing, and this goes
    on tape too, along wich the date and time and both
    numbers, ~curs and theirs. At this point the CAMA
    machine sends the billing details of th~ call to
    the real heart of the C~MA, in the Toll `.. =.
    
    Ncm the ~ay the phone company sends si~nals ~n
    their lines is wiCh frequencie~. When an inter-toll
    line, or t-~`nk, is idle, it has present on it a tone
    of 2CC~ Cycles. This tore tells senders who are
    searching for idle tru~ks tbat this one is aK to use
    Wnen the line is seized and used, the tone is not
    present.
    
    Control of ycur telephone line is done by
    you. W~er, you hang up, the CC relays tbat to
    the senders and incoming senders on the trunk
    and then they disconnect.
    
    I ~ cwe;er, you were to send a 2630 cycle
    tone dcwn your line, your CO ~ould not do a
    tning because it ~sr,'t desigred to re~ct to a
    26-0 cycl- tone. But the intertoll trunis would
    think you Pung up, because 2600 cycles means tre
    line is dle. So they wouid disconnect you from
    the CO ct the end of the chain. When you release
    the 2600 tore, the ircomin~ sender would now be-
    lieve the line has been seized, and will wait for
    the ME digits.
    
    Mea-;while, back at the CO(you~s3 the CAMA is
    billing you for th-e initial call you made. If it
    was for inforration, the rate is zero ½~minute.
    However, ir.formation calls don't take too lor`g so
    the pe~ple w~o go over the pa~er tape at the end
    of the month may spot something fishy. 800 nu~hers
    are a differer.t story, but they'd better be valid.
    The MF disits and 26CO cycles are passin~ thrJ th.e
    CO ur~otic~d all this ti~e.
    
    When ycu ser.d MF digits, the incoming sender ~t
    the far end translates the~ and routes you to the
    correct C0, if its in tbat area code. If it is, and
    you send t-~ area code along with the other dig~s
    the machine will overload ard the call won't go
    thru. If you h~d dialed infor~ation or a wats line
    based in a different area from the desired nu~ber,
    the sender will reraute you to that area anl then
    to that nu~ber. Most boxers call information in a
    differeht city fron wLere they war.t to call and then
    send are~ c~de with digits to reroute.
    
    Since all calls are sh~wn on t~e paper tape, a
    pay phone is the only safe way to go. And be sure
    to change phones too.
    
    tos 4 - EtES
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