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System architecture 17
Firmware
-
This portion of the memory is a non-volatile Read
Only Memory (ROM) used for storage of all system fiiware.
The ROM is programmed during manufacture and the instructions
are permanent and indestructible. It stores the basic rules of
operation necessary to initialize the system
and
bring it into a
working state. A recovery or “trap sequence” is included in
fiiware which is automatically invoked in response to power-on,
system reset, or when certain faults are detected.
Overlay
-
This portion of the memory may be loaded with
various non-resident programs as required during automatic
diagnostics, service order change, traffic measurement, or
maintenance.
Software
-
The remainder of this memory page is reserved for all
of the system software such as the call processing and optional
programs. Additional software storage capability is provided by
the incremental addition of more memory pages within this
category.
Input
/
Output Addresses
-
There are no RAM modules utilized
for this page. Instead the address range is reserved for
Input/Output (I/O) device addresses. These devices include
._
signaling for peripheral equipment along with magnetic tape and
terminal assignments.
Network equipment
Network equipment consists of network circuit cards which perform the
digital switching of voice and data signals, peripheral signalling cards which
perform scanning and signal distribution. , and service circuit cards, such as
tone and digit switches, which provide call progress tones and outpulsing as
instructed by the CPU. Network circuits employ Pulse Code Modulation
(PCM) and Time Division Multiplexing (TDM) to perform the switching
function.
Loops and Superloops
Network equipment interfaces with peripheral equipment via digital
multiplexed loops. A loop is a bidirectional path between Network
equipment (NET) and Peripheral equipment (PE) for voice, data and
signalling information. Upon commands from the CE, the network
establishes a path, linking a specific input to a specific output.
System overview 553-3001-l 00