Software Overview; General; Physicallayer; Schedulinglayer - Mitel SX-200 Practices

5
' SOFTWARE OVERVIEW
General
5.1
The SX-200 DIGITAL PABX software is divided into two separate sections, one to
run the Main Control processor and one to run the Peripheral Control processors.
Upon power-up, Call Processing and Maintenance routines are downl,oaded from the
disk to the Main Controller Memory using Direct Memory Access (DMA). The Main
Controller executes the Maintenance routines and logs all major occurrences to the
disk, non-volatile random access memory, Main Control Card 7-segment displays,
and the maintenance terminal (if equipped).
When the system is functional, the software relevant to the peripheral systems is
downloaded from the Main Controller Memory to each Peripheral Controller's Memory.
The transfer is accomplished via the Message Subsystem link, using a single 64 kilobit
per second channel in each direction, for each Peripheral Controller (Peripheral
Control Card or Bay Control Card).
Each software section has its own layers to carry out system functions.The layers
defined below apply to both controllers unless otherwise specified.
Physical layer
5.2 The physical layer consists of the operating hardware such as the microprocessor, its
associated memory, and input/output devices.
Scheduling layer
5.3 This layer provides for scheduling of the different events to be handled.
Communications layer
5.4
This layer takes care of the Message Subsystem software. The messages between
the processors are sent in HDLC formatted packets. The formatting, sending,
receiving, and unpacking of these messages is handled by the Message Subsystem
software. Messages are transmitted using a single 64 kb/s channel in each direction.
If required, the transmission rate can be increased to 128 kb/s by using two
channels.
Message Subsystem
5.5
The Message Subsystem is used as a communication link between the Main
Controller and the Peripheral Controllers. Initially the Message Subsystem is used to
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