Project Files
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FMU - 128 line High Reliability
Hot Swap Phone Switch
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Subscriber
Solutions had won a Bureau of Prisons contract to deliver
a high reliability modular PBX system and had eighteen months
in which to deliver a fully working system. Bolton Engineering
worked closely with Subscriber Solutions to create a detailed
system specification so that the many subsystems could be
designed and tested in parallel. Boards were designed to
be removed from or inserted into the system while the power
was running without losing ongoing calls ("hot swapped").
Redundant TDM (Time Division Multiplex) highways and control
busses were implemented to ensure that single-point failures
did not stop other system elements from working.
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Workscope
- Translated 400 page customer requirements document
into 50 page technical specification
- Designed all schematics, Programmable Logic Devices
(9 PLDs) and 5 circuit boards
- Wrote board-level firmware for three boards, and integrated
voice / tone detection and generation IP.
- Wrote specification for backplane and power supply
- Tested and qualified design
- Passed all regulatory testing on first testing: FCC
parts 15, 68, UL 1459, UL 1950, IEC 1000-4
- Controlled documentation and synchronization between
5 PCB Designs, 9 PLDs, and 3 software sets.
- Produced 70 page hyper-linked product reference guide
describing system operation
- Completed project over a fifteen month time frame
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Station Card
- Supports six phones
- Includes one spare interface that may be allocated
to any phone line in the event of a failure
- Generates dial tone, plays back voice prompts
- Detects “Yes/No” and DTMF tones
- Interfaces to backplane, supports card hot-swap
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Central Office Card
- Connects to six central office lines
- Manages all aspects of phone control
- Generates DTMF, plays back voice prompts, detects
call completion/end, detects SIT tones, times calls
for billing
- Detects “Yes/No” and DTMF tones
- Interfaces to backplane, supports card hot-swap
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Interchassis Bridge Board
- Connects two separate chassis together over high-speed
multiplexed link
- Minimizes frame “slip”
- Detects errors and reports link integrity to
CPU
- Interfaces to backplane, supports card hot-swap
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T1 / E1 Line
- Interfaces to central office T1/E1 line (48 or
64 DS0 lines)
- Manages facilities link, message channel (TCP/IP),
and diagnosticS
- Generates DTMF, plays voice prompts, detects
call completion/end, detects SIT tones, times calls
for billing
- Detects “Yes/No” and DTMF tones
- Interfaces to backplane, supports hot-swap
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Backplane (not
shown)
- Specified by Bolton Engineering, designed by vendor
- Up to 18 cards per backplane
- Up to 2 backplanes per system
- Provides breakout for I/O, station connectors,
T1/E1 wiring, and power supply cabling
- Staged backplane connector pins support card
hot swap
Power Supply (not shown)
- Specified by Bolton Engineering, designed by
vendor
- Supports card hot swap
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CPU Card (two per
system)
- Runs Linux operating system
- Manages call billing database
- Runs system diagnostics
- Controls TDM bus switching
- Includes two V.35 lines, one ethernet port, V-35,
RS-530, RS-232, RS-422 serial interfaces, IDE disk
controller
- Generates dial tone, plays voice prompts
- Interfaces to backplane, supports card hot swap
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Consumer and Computer
