MT90220
Serial
Streams
Transmitter
Cell RAM
ATM In
UTOPIA L2 Interface
Cell_In_Control
FIFO Link 0
(see Note 1)
ICP Cell Modifier and
Cell Scrambling
Link 0
Link 1
P/S
P/S
ICP Cell Modifier and
Cell Scrambling
FIFO Link 1
(see Note 1)
FIFO Link 7
(see Note 1)
ICP Cell Modifier and
Cell Scrambling
Link 7
P/S
TX Utopia FIFO
Group 0
from IDCR Generator
Round Robin Scheduler
and FIFO Selection
and Adaptive Shaper
(1 of 4)
TX Utopia FIFO
Group 3
Filler Cell
to Cell_In_Control
IDCR Generator
(1 of 4)
Idle Cell
ICP Cell Group 1
ICP Cell Group 2
ICP Cell Group 3
ICP Cell Group 4
Transmitter
Reference
Link Timing
ICP Cell Handler
ICP Cell Buffer RAM
Next ICP Cell Group 1
Next ICP Cell Group 2
Next ICP Cell Group 3
Next ICP Cell Group 4
Note 1: This FIFO is the
TX UTOPIA FIFO when
the link is configured in
UNI Mode and it is the
TX LINK FIFO when it is
configured in IMA Mode.
Micro I/F
Figure 3 - Functional Block Diagram -Transmitter in IMA Mode
2.2 The ATM Transmission Convergence
with the IMA transmit protocol) for transmission over
the PCM Interface.
The Transmit Convergence (TC) function is common
for both the IMA and UNI modes. It integrates the
circuitry to support ATM cell payload scrambling,
HEC generation and the generation of Idle/Filler/ICP
cells for use with the T1 and/or E1 trunks. Each of
the eight MT90220 ATM TC circuits can use the
In cases where the TC block requests a cell to be
transferred to any of the PCM Interfaces and the TX
UTOPIA FIFO has no cell ready for transmission,
then the TC block will automatically send an IDLE
cell (in UNI) or a Filler cell (in IMA mode) to the line.
The default values for the Idle and the Filler cells
comply with the ATM IMA Specification and are pre-
loaded in the MT90220 following a reset. The TX
Cell RAM Control register can be used to re-
initialize the TX Cell RAM.
43
polynomial X + 1 to scramble the ATM cell payload
field. The MT90220 ATM cell payload scrambling
function can be disabled.
8
2
The ITU I.432 polynomial X + X + X + 1 is used to
generate the HEC field of the ATM cell. By default,
6
4
2
the ATM Forum polynomial X + X + X + 1 is added
to the calculated HEC octet. The addition of the ATM
Forum polynomial can be disabled.
2.2.1 TX Cell Ram and TX FIFO Length
The internal TX Cell Ram can hold up to 64 cells.
The following six cells are reserved for MT90220
operation:
The resulting calculation is then over-written on the
HEC field and the ATM cell is ready (i.e., complies
•
one ICP cell for each IMA Group for a total of
four cells
10
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