Instruction manual

GLOSSARY
Foreign Exchange (FX)
A central office other than the one providing local access to the public telephone
network.
Foreign Exchange Trunk
A telecommunications channel that directly connects the system to a central office
other than its local central office.
Foreign Numbering Plan Area Code (FNPA)
Frame
An area code other than the local area code; also known as the “other area code.”
The foreign area code must be dialed to call outside the local geographical area.
Slip
A slip is the deletion or repetition of a frame. Slips are caused by differences in clock
frequencies. Generally, a slip involving the synchronization will result in most or all
spans experiencing misframes. Slips are not caused by noise on the transmission
line.
Framing
Framing is the process of segmenting and identifying the information carried on a
digital facility.
Ground-Start Trunk
On outgoing calls, System 25 transmits a request for services to the distant switching
system by grounding the trunk ring lead. When the distant system is ready to receive
the digits of the called number, that system grounds the trunk tip lead. When the
System 25 detects this ground,
the digits are sent. (Tip and ring are common
nomenclature to differentiate between ground-start trunk leads.) On incoming calls,
detection of ground on the tip lead is sufficient to cause the call to route to a
predetermined destination,
normally the system attendant group. No digits are
received.
HFAI: (Hands-Free Answer on Intercom)
Home Numbering Plan Area Code (HNPA)
The local area code; also known as the “home area code.” The local area code does
not have to be dialed to call numbers within the local geographical area.
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