Administrator's Guide

Trunks and trunk groups
Issue 5 October 2002 1905555-233-506
CO — Central Office
CO trunks transmit dialed digits for outgoing calls but not for incoming calls. Use
CO trunks when you want all incoming calls go to the same destination, such as
an attendant or a voice menu system. Individual users can place outgoing calls
without attendant assistance. CO trunks typically connect your switch to the local
central office, but they can also connect adjuncts such as external paging systems
and data modules.
CPE — Customer-Provided Equipment
Use CPE trunks to connect adjuncts, such as paging systems and announcement or
music sources, to the switch.
NOTE:
You can connect some types of equipment to the switch by trunks without
administering a CPE trunk group. For example, trunk port interfaces can be
assigned on system screens for Music-on-Hold Access (Feature-Related
System Parameters screen) or voice and chime paging (Loudspeaker Paging
and Code Calling Access screen).
DID — Direct Inward Dialing
DID trunks carry incoming calls directly from the local central office to your
switch. These trunks transmit the digits your switch needs to route incoming calls
to specific extensions. Use DID trunks when you want people calling your
organization to dial individual users directly without going through an attendant
or some other central point.
DIOD — Direct Inward/Outward Dialing
DIOD trunks are two-way trunks that transmit dialed digits in both directions.
Thus, use DIOD trunks when you want a two-way trunk group with the
convenience of direct inward dialing for incoming calls. DIOD trunks are used
mostly outside North America, and typically they connect the switch to a local
central office.
In North America, use tie trunks for applications that require two-way
transmission of dialed digits. In the U.S., trunks that transmit digits in both
directions are sometimes called “smart trunks” and are administered as T1 tie
trunks.