ipLDK-60 SERVICE MANUAL
DIGITAL KEY TELEPHONE SYSTEM
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2.2 Switching
2.2.1 Back plane Architecture
ipLDK-60 system has PCM highway called MPX bus to interface voice CODECs on the MBU and Option boards to main
switching device ACT2.
For extension boards and expansion KSU on which additional PCM highway is needed, system back plane architecture
called ISC highway provides interfacing custom blocks such as DBID and GSL12 in ACT2 on the MBU.
The ACT2 has the DBID block and the two GSL12 blocks that provide a MPX bus and 15 pairs of ISC highways. A MPX
bus is composed of 36 PCM time slots that are assigned to basic voice CODECs on the MBU and voice CODECs on
the CO ports.
Expansion MBU also has custom back plane interface blocks such as DBID and GSL12 to transmit and receive “B” and
“D” channels information for stations and circuits
A. EXP_ISC Highways
EXP_Inter-System Communication (EXP_ISC) Highways are buses on the back plane that distribute digitized voice and
signaling data, and carry out board level communication throughout the system connector(s). These highways are
provided in transmitting/receiving pairs and there are a total of 3 highway pairs in ACT2. Communication on each
highway is at 8.192Mbits per second in a time division multiplexed format. Time division multiplexing creates “channels”,
or time slots, that carries digitized voice, signaling data, and High-Level Data Link Control (HDLC) protocol information.
Voice (“B”) channels carry digitized voice signals. Signaling (“D”) channels are employed for channel specific signaling
implementation.
B. Channel Allocation
The Main Board Unit (MBU) determines which time slot on which ISC highway will be used to transmit and receive “B”
and “D” channels information for all stations and circuits. The DBID or GSL12 block in ACT2 the “B” and “D” data onto
the system highway at the appropriate time slot. Any port can be assigned to transmit on any transmit “B” channel and
receive on any receive “B” channel. The “D” channels can also be flexibly assigned and controlled independently of the
“B” channels. The HDLC inter-board communication channel on each highway is also controlled by the main processor
on the MBU and placed on the highway by the DBID on peripheral board.
C. Voice Channels
PCM signals received from the digital instrument are placed on a back plane highway transmit “B” channel and sent to
the MBU where gain modification and/or conference summations take place. The output is placed on a back plane
highway receive “B” channel for the receiving port. All voice channels are fully 64Kbps digital time slots.
2.2.2 Signaling Channels
The “D” channels are 16Kbps channels designed to carry channel specific signaling information and low-speed user
data.
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