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D-channel handler
Introduction
PRI differs from other common channel signaling protocols; it does not use
external assistance (such as MSB7 or LIU7) to cope with the call control
messages. All signaling functions transport from the external peripheral
module up to the computing module by means of the ISDN signaling
processor (ISP).
Hardware configuration
The D-channel handler (DCH) consists of two processors:
Functionality
The DTCI master processor communicates with the ISP through shared
memory. Figure 3-1 illustrates the relationship between the D-channel
handler environment and the various ISDN layers.
master processor (MP)—performs high-level processing for the
D-channel such as link access procedure on the D-channel (LAPD)
ISDN signaling preprocessor—used by the ISDN digital trunk controller
(DTCI) for D-channel signaling; supports up to 32 D-channels on a
single DTCI
— eliminates the need to provision signaling terminal cards for
D-channel signaling
— controls the transmission and reception of high-level data link
control (HDLC) frames
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
3-1
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