Comdial DXP Plus Series, Руководство пользователя

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ISDN–PRI Interface
Integrated Services Digital Network (ISDN) provides integrated voice and data over a common telephone
company facility. There are two methods of ISDN access currently available: ISDN–BRI (basic) and
ISDN–PRI (primary). ISDN–BRI provides a way for subscribers to get digital service from the telephone
company supplier for two telephones or a telephone and a data device over one special pair of wires.
ISDN–PRI provides a way for subscribers to get digital service from the telephone company supplier for
24 lines over two special pairs of wires. This latter method is the concern of this publication.
ISDN–PRI access directly connects a multiple-station, digital communications system to the telephone
company’s ISDN network through a single high-speed line. This high-speed line is commonly known as
T1 in North America and consists of 24 digitized channels. ISDN–PRI access consists of a grouping of 23
voice channels (B–channels) and one signaling or control channel (D–channel). B–channels are clear
channels suitable for voice or data transmission while the D–channel is a packet-switched link for call
set-up and signaling. When you use ISDN–PRI access with T1, one of the T1 channels serves as the
signaling channel. This arrangement is sometimes referred to as 23B+D ISDN service.
The DXPRI is a circuit card that you install on a revision B or later DXPT1 line board with
special-purpose firmware to provide ISDN–PRI access to the digital communications system. The DXPRI
card handles the D–channel signaling protocol and passes messages to the DXPT1 board. A single
DXPRI card can control multiple DXPT1 boards when you tie the boards together through board
programming action. This arrangement (known as NFAS or Network Facility Associated Signaling)
allows the system to derive 24 B–channels from all boards except the one where installers have added the
the DXPRI card. When installers do this, the DXPT1/DXPRI combination that provides the control is
designated as DXPT1–PRI; and the boards being controlled are designated as DXPT1–NFAS. The NFAS
boards do not require a DXPRI card as they are slaves to the master –PRI board. Throughout the
remainder of this publication, the term T1/PRI means a T1 board specifically configured for ISDN–PRI
operation be it either a DXPT1–PRI or a DXPT1–NFAS board.
Since central office protocols differ, the DXPRI card supports several protocol arrangements and provides
interface support for several signaling types. The programmer and the end user can select the interface
support that the system needs for a particular application. The support they choose determines how the
telephone company treats the signal.
The DXPRI card provides a calling number identification feature that provides the following services:
delivery of network provided calling numbers, calling line identification presentation (CLIP), or
automatic number identification (ANI). On originated calls, the system automatically provides the calling
number if available; otherwise, it provides the default directory number. For incoming calls, the called
station displays the calling number if available; otherwise, the display shows information determined by
station class of service programming. The system programmer can customize the caller ID parameters for
outgoing calls as site requirements dictate.
Introducing The T1/PRI Line Board
The revision B or later DXPT1 board with special-purpose firmware serves as host for the DXPRI card
and gives gives the digital communications system the capability to handle up to 24 channels of voice
and/or data transmissions over a single four-wire cable using multiplexing techniques. The DXPT1 board
includes a customer service unit (CSU) to eliminate the need for an external CSU.
Defining T1/PRI Operation
T1/PRI is the digital two-way transmission of telecommunications over a single high-speed circuit. Up to
24 separate voice or data transmissions form digital pulses that are transferred at the rate of 1.544 million
bits per second (Mbps) over the T1/PRI trunk. At the receiving end, the digital pulses are decoded into 24
separate circuits.
TAB003-PLS, page 19
DXP Plus General Description GCA40–130
Understanding The Features – 85A