Information Technology Reference
In-Depth Information
dedicated line connecting two telephone switches within a single organization. The fol-
lowing is a list of trunk types:
Interoffice trunk
connects two CO switches. Also called a PSTN switch trunk.
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Ta n de m t r u n k
connects central offices within a geographic area.
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To l l - c o n n e c t i n g t r u n k
connects the CO to the long-distance office.
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Intertoll trunk
connects two long-distance offices.
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Tie trunk
connects two PBXs. Also called a private trunk.
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PBX-to-CO trunk or CO-to-PBX business line
connects the CO switch to the enter-
prise PBX.
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Figure 14-2 shows an example of the PSTN. All phones connect to their local CO via the
local loop. Calls between Phones 1 and 2 and between Phones 4 and 5 go through interof-
fice trunks. Calls between Phones 2 and 3 go through tandem trunks within a region.
When you place calls between Texas and Massachusetts, they are forwarded to the long-
distance toll provider via a toll-connecting trunk and are routed through intertoll trunks.
Ta n d e m
Trunks
Local Loop
CO
CO
Phone 1
Houston, TX
Ta n d e m
Interoffice
Trunk
Phone 4
Boston, MA
CO
CO
Phone 2
Houston, TX
Phone 5
Boston, MA
CO
To l l
To l l
To l l C o n n e c t i n g
Trunk
Phone 3
Pearland, TX
Intertoll
Trunk
(AT&T, Verizon, Sprint)
To l l C o n n e c t i n g
Trunk
Local Loop
Figure 14-2
Local Loops and Trunks
Ports
Yo u c a n u s e s e v e r a l p o r t s t o c o n n e c t t o v o i c e e n d s t a t i o n s ( p h o n e s ) a n d p r i v a t e v o i c e
switches:
Key
To p i c
Foreign Exchange Station (FXS)
endpoint device such as traditional telephones or fax machines. It provides line
power, dial tone, and ring voltage.
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