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12-12 Issue 5 January 1998
Stratum 3 clock is an optional external hardware adjunct for DEFINITY ECS that is
more accurate than standard systems. Stratum 3 clock has a maximum of 2.5
minutes of allowable error per year. The standard clock used in DEFINITY ECS
and many switch systems is a stratum 4E clock, which allows approximately 17
minutes of error per year.
ISDN
Lucent’s DEFINITY ECS provides complete ISDN support for small systems with
20 telephones up to large systems with 25,000 telephones. Demonstrating its
role as a leader in making ISDN a universal reality, Lucent Technologies makes it
possible for anyone connected to DEFINITY ECS to benefit from ISDN capabili-
ties and features.
ISDN eliminates the need for multiple, separate access arrangements for voice,
data, facsimile, and video services and networks. Using the same pair of wires
that now carry simple telephone calls, ISDN can deliver voice, data, and video
services in digital format.
ISDN is a global access standard established by the Consultative Committee for
International Telephone and Telegraph designed to help you move and manage
information with unprecedented ease and productivity — anywhere in the world.
ISDN uses a layered protocol that conforms to layers one, two, and three (physi-
cal, link, and network layers) of the seven-layer Open Systems Interconnect Ref-
erence Model of the International Standards Organization.
DEFINITY ECS supports the two major interfaces specified in the ISDN standards
— Primary Rate Interface and Basic Rate Interface.
■ Primary Rate Interface is used for connecting premises equipment such
as switches to the network, and acts as a powerful interface between
intelligent equipment such as switches and computers.
■ Basic Rate Interface is used for connecting telephones, computers,
personal computers, and other desktop devices to higher-order
equipment such as a switch. BRI can also be used as a trunk interface, for
example, connecting a Central Office to a PBX.
Both Primary Rate Interface and Basic Rate Interface are based on the same
common building blocks — the use of a common interface to a transmission path
that is divided into channels. Both Primary Rate Interface and Basic Rate Inter-
face use two types of channels for communication:
■ Bearer channels are the communications links in ISDN. They provide
64-kbps digital communications service for voice, data, video, and other
information transmission.
■ Delta channels, sometimes known as data channels, are the signaling
links in ISDN. They carry call-control and call-related information, such as
caller ID, between ISDN endpoints.