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| Trunk Type | Description |
| Loop Start | An analog circuit intended primarily for key systems and older PBXs. This is the type of circuit used in most residences and small businesses, and it supports Caller ID. Loop start trunks can present problems when used with PBXs. |
| Ground Start | An analog circuit preferred for use with PBXs because the signaling prevents “glare” (an incoming and outgoing call seizing a trunk simultaneously), supports Caller ID, and provides positive disconnect once a caller hangs up. |
| Tie | A private circuit that directly connects two systems. Can be analog or digital. Using a
tie trunk, a user on one system can call an extension on another system by dialing the
extension number, or an access code and then the extension number. Tandem tie circuits—analog E&M tie line, T1 emulated E&M, or a PRI tie line—can be used for networking if the system is in Hybrid/PBX mode. The user dials only the nonlocal extension number; no access code is required. |
| Direct Inward Dial (DID) | An analog or digital circuit that allows incoming calls to be routed directly to an extension or Calling Group without the assistance of the company’s receptionist. DID circuits provide inbound calling only. |
| T1 | A digital trunk that provides 24 circuits over a single copper wire pair. Can be used for
voice and/or data. In voice operation, a T1 trunk can be programmed through the system to emulate a ground-start, loop-start, tie, or DID trunk. T1 operation also gives customers access to special services, such as inbound 800 or WATS for incoming, toll-free service. T1 data operation allows high-speed data communications over the public switched network (Switched 56 service)— provided by the INAP board. It also provides data tie lines to connect one MERLIN MAGIX system to another, or to a DEFINITY system. |
| Primary Rate Interface (PRI) | A digital trunk that provides 24 circuits over a single copper wire pair. Can be used for
voice and/or data. Primary Rate Interface is a standard offering of ISDN (Integrated Services Digital Network). PRI has a special signaling channel that allows a variety of advanced services such as Automatic Number Identification (ANI) and Dialed Number Identification Service (DNIS). These are particularly useful in call centers. |
| Basic Rate Interface (BRI) | A digital trunk that provides three circuits (two for transmitting information, one for signaling)
over a single copper wire pair. Can be used for voice and/or data. Basic Rate Interface is a standard offering of ISDN (Integrated Services Digital Network). BRI has a special signaling channel that allows a variety of advanced services such as Automatic Number Identification (ANI) and Dialed Number Identification Service (DNIS). These are particularly useful in call centers. |
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