A CDE Definition
The state of a telephone line that allows dialing and transmission but prohibits incoming calls from being answered. The phone is off-hook when the handset is lifted off the base of a stationary phone or when Talk is pressed on a portable phone.
The term stems from the days when the handset rested on an actual hook. When it was removed, a spring caused contacts to press together, closing the circuit from the telephone to the switchboard in the central office (CO). When a handset is placed back on the base, it is said to be "on-hook," and the phone can receive a call. See central office.
There Really Was a Hook
A local telephone company switching center. There are two types of central offices (COs). The first is called an "end office" (EO) or "local exchange" (LE) and connects directly to the outside plant, which is the feeder and distribution system to homes and offices. The end office (often called a "Class 5 office") provides customer services such as call waiting and call forwarding.
The second type is the tandem office (also toll office or tandem/toll office), which is a central office that does not connect directly to the customer. Toll call record generation and accounting used to be handled in the tandem offices. Today, the billing is mostly done in the end offices. There are more than 25,000 central offices in the U.S. See LEC, IXC and LATA.
High-Tech Switching in the 19th Century
Before/After Your Search Term
|OEM Service Release 2||off-premise extension|
|Oersted||off-site data protection|
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