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3-2 D-channel handler
Figure 3-1
D-channel handler and ISDN layer comparison
Layer 3 messages destined for the PBX are packaged into layer 2 frames by
the ISP. These frames are transmitted by the high-level data link control
(HDLC) circuitry (resident in the ISP) onto a DS-1 channel. The DS-1 is a
24-channel (64 kbit/s each channel) carrier that provides the medium of
communication between the DMS-250 switch and the PBX.
The ISP card, located in slot 16 of the DTCI shelf, provides the capability to
do ISDN-specific front-end processing for PRI applications. The ISP is
essentially the layer 1 termination point for DTCI D-channels. The ISP
contains a host processor (68020), HDLC circuitry, and a LAPD state
machine. These entities provide layer 1 and layer 2 protocol handling for an
ISDN PRI.
HDLC circuitry is used to send and receive ISDN LAPD frames. The
circuitry terminates up to 32 data channels, and each channel supports up to
64 kbit/s.
The DTCI peripheral has the same configuration as a digital trunk controller
(DTC), but the DTCI requires an ISP card in each unit. The special tone
receiver card is not supported with a DTCI.
Installation
The PRADCH-level of the MAP terminal posts and maintains the DCH in
the DTCI. To reach the PRADCH level from the command interpreter level
of the MAP terminal enter the following command:
>MAPCI;MTC;TRKS;TTP;PRADCH
297-2521-106 Standard 23.01 March 2001
ISDN architecture
Layer 3
Layer 2
Layer 1
D-channel handler environment
DTCI master processor
Shared memory
ISDN signaling preprocessor
High level data link
control circuit
DS-1 channel
Rx
D-channel
handler
Tx
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