How Long Distance Works
Basic information on how local and long distance phone companies work - call waiting, call forwarding, call transfer and conferencing, caller id, and voicemail.
Cell Phone No Contract
Phone Bill Review
Local Central Office
Somewhere near to you is your
local phone company's "central office", or "wire
center". All of the telephone lines (wires) in your
home or office connect directly to this office. The
central office contains a "switch" - this is a term which
refers to the devices which route, or switch, telephone traffic
from one destination to another.
Local Telephone Calls
Local telephone calls within a
municipal area are often completed within a single central
office; that is, if the call is destined for a telephone
which is served by the same central office that serves the
calling telephone, the central office simply switches the call
from the incoming line to the destination line as defined by
the called number. The central office does this by
analyzing the dialed numbers.
Switched Long Distance
When you make a long distance
phone call, your local central office again analyzes the number you
have dialed. If the dialed number is inside of your LATA
- the geographical area in which your local telephone company
is legally permitted to carry long distance toll calls, it
again directs the call to another local central office, often
operated by the same local phone company, which completes the call.
If the dialed long distance phone
is destined outside of your LATA, your local central office
queries its database of PIC (Primary
Interexchange Carrier - simply means primary long distance
company) codes, to see which long distance phone company you have
selected for the line making the call. It then switches
the call to lines connected directly to the long distance
phone company's nearest switch, or POP (point-of-presence). The
long distance company switch again analyzes the dialed number, and
routes the call across the long distance network to the POP
nearest to the called number. That POP in turn routes the
call back to the local central office nearest the destination
telephone, and the local central office completes the call.
Dedicated Long Distance
The switched long distance phone calling described above is so named because the originating phone call must be switched from the local central office to the long distance carrier's POP. Dedicated long distance does not require this switching. Instead, the customer has installed a dedicated circuit between the customer's premises and the long distance phone carrier's POP. The dedicated circuit is typically called a "T1", which provides 24 channels for long distance calls. Just think of a T1 as 24 phone lines in one.
The local phone company is not involved in switching the call to the dedicated long distance carrier. Normally, the customer's telephone system switches the call to the dedicated line at the customer's facility. The customer will enjoy significantly lower per minute toll charges from the long distance company for dedicated service, but must pay a monthly fee (typically $300 and up) for the dedicated lines, and must, in general, sign a term contract for long distance service. There is also special equipment required at the customers site to connect to the dedicated service. In general, dedicated service is used only by customers who routinely use 20,000 - 30,000 minutes per month of long distance service.