MT90840
Preliminary Information
2-236
Functional Description
The MT90840 Distributed Hyperchannel Switch is a
large switching, multiplexing, and rate-adapting
device. The MT90840 bridges serial-bus telecom
components, using the Mitel ST-BUS or other
industry-standard serial buses, onto a higher speed
“backbone”. Mixed data, voice and video signals can
be time-interchanged or multiplexed from serial Time
Division Multiplexed (TDM) streams onto a high
speed parallel bus. The parallel bus can be used for
interconnect, or an external framer can be connected
to the parallel bus to access serial isochronous
backbones operating at up to 155 Mbps SONET
rates (STS-3).
The MT90840 Distributed Hyperchannel Switch
supports real-time multimedia applications through
constant delay switching. Multimedia data at N x 64
kbps rates uses N bytes (“time slots”, or “channels”)
per 125
µ
sec frame. This is also referred to as
hyperchannel data. To ensure the integrity of data at
N x 64 kbps rates, the network must ensure that the
N bytes in a given input frame remain together as a
frame, and arrive at the destination as a frame. The
MT90840 supports this requirement by providing
constant delay (frame integrity) which ensures that
the multiple time slots of associated data remain in
the intended order.
Total TDM channel capacity of the MT90840 at
maximum data rates is:
• 512 serial input time slots,
• 512 serial output time slots,
• 2430 parallel input time slots, and
• 2430 parallel output time slots.
The number of time slots available is dependent
upon the selected data rates, and is reduced at lower
data rates.
Figure 1 shows the MT90840 functional block
diagram. The figure shows the TDM data paths and
the device interfaces.
The MT90840 has three main TDM data paths:
• Transmit Path: serial port input (STi) to parallel port
output (PDo),
• Receive Path: parallel port input (PDi) to serial port
output (STo),
• Bypass and Parallel-Switching: PDi to PDo.
In addition, Mitel Message Mode capabilities allow
the user to force data on TDM output time slots and
to monitor TDM input time slots through the
microprocessor port.
The MT90840 has four main interfaces:
• the serial TDM bus interface (STi, STo and timing),
• the parallel TDM bus interface (PDi, PDo and
timing) with programmable control outputs (CTo),
• the microprocessor (CPU) interface,
• the test interface (JTAG).
The MT90840 supports four major timing/switching
modes:
• TM1/Ring Master: PDo timing slaved to STi/o
timing, PDi timing elastic;
• TM2/Ring Slave: PDo and STi/o timing slaved to
PDi;
• TM3/Bus Slave: PDo and PDi timing tied together,
STi/o timing slaved to parallel bus;
• TM4/Parallel Switching: parallel channel switching
from PDi to PDo.
Other features of the MT90840 are programmable for
individual TDM channels on the serial and parallel
ports (per-channel features):
• Mitel Message Mode,
• Per-channel output enable,
• Per-channel bypass (parallel bus),
• Programmable CTo control outputs (parallel bus),
• Per-channel direction control (serial bus).
Device Operation
Time Slot Interchange Operation (Switching)
The MT90840 provides access and time slot
interchange (switching) functions between the serial
and parallel TDM data ports. Switching is provided
on three paths: transmit (serial input to parallel
output), receive (parallel input to serial output) and
bypass/parallel-switching (parallel input to parallel
output). Switching functions between serial data
streams are not provided.
The MT90840 guarantees wideband or
hyper-channel data integrity through the switch by
using constant delay switching. This is done by
storing a full frame (125
µ
sec) of data at the input
rate and then, under control of the Connection
Memory for that path, reading the frame at the output
data rate (frame integrity). Therefore the Transmit
Path and the Receive Path each have separate Data
and Connection Memories.
Switching in a given data path is controlled by
programming the Connection Memory for that path.
Each output time slot has a control-address in the
path’s Connection Memory. Each input time slot has
Содержание MT90840
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