Lucent Technologies 5 manual Issue

MERLIN LEGEND Communications System Release 5.0	Issue 1
System Manager’s Guide 555-650-118	June 1997

2About the System

Incoming Trunks Page 2-14

The types of trunks are:

■Loop-Start Lines (Incoming and Outgoing Calls). Provide incoming and outgoing calls and are intended primarily for single-line telephones and older PBXs. They are the simplest (often the least expensive) and most common facilities in the nationwide telephone network. Although they are not appropriate for some situations, they are necessary for others (for example, some caller identification services).

■Ground-Start Trunks (Incoming and Outgoing Calls). Provide a signal at the beginning and end of incoming and outgoing calls to determine the availability of a trunk before the CO routes an incoming call on it. Also, when either the caller or the called party hangs up, the entire circuit is disconnected and dropped. These trunks were introduced to solve the problems that PBXs encounter on loop-start trunks (namely, glare and unreliable disconnect), as described in the Introduction booklet.

■Tie Trunks. Private lines that directly connect two communications systems. Using a tie trunk, a user on one system can call an extension on another system by dialing an access code and the extension number or simply the extension number.

In more complex tie trunk configurations, a person can tie into another system and use a trunk that does not exist on his or her own system. For example, in a company with locations in New York, Chicago, and Los Angeles (with tie trunks between New York and Chicago, and Chicago and Los Angeles), users in New York can access a Los Angeles trunk and make a local call as if they were in Los Angeles themselves.

■Direct Inward Dial (DID) Trunks (Incoming Calls Only). Provide fast access to specific individuals; incoming DID calls can be routed directly to an extension or calling group without system operator assistance.

■Digital Facilities. MERLIN LEGEND supports two different types of digital facilities: Digital Signal 1 (DS1) and, in Release 4.0 and later systems, National Integrated Services Digital Network 1 Basic Rate Interface (abbreviated NI-1 BRI) facilities. T1, PRI, and BRI are the system’s interfaces to these Integrated Services Digital Network (ISDN) facilities, which provide end-to-end digital connectivity and switched connections to other networks. All three interfaces allow high-speed data transfer.

—National Integrated Services Digital Network 1 Basic Rate Interface (Incoming and Outgoing Calls). One NI-1 BRI facility carries the equivalent of three “lines.” Two are called B-channelsand provide voice and data communications services. A third D-channel controls signaling and maintains operations on the B-channels.

—Digital Signal 1 Facility Programmed for Either T1 or Primary Rate Interface Operation (Incoming and Outgoing Calls). One Digital Signal 1 (DS1) facility provides the equivalent of 24 lines, called channels. In Release 4.0 and later systems, the DS1 facility can be programmed to operate in one of three ways: