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7.0 OAM Functions
7.4 PM Processing
RS8234
Datasheet for RS8234 xBR ServiceSAR
N8234DS1B
7.4.3.1 Generation of
Forward Monitoring PM
Cells
The segmentation coprocessor generates a forward monitoring PM cell at the end
of each PM block, as defined by the BLOCK_SIZE field in the SEG_PM table
for any PM_INDEX. It determines the point to generate a forward monitoring cell
by following these processes:
At the point of initialization of PM processing or when a forward monitor-
ing cell is sent, the Seg coprocessor sets the BLOCK_COUNT field to
zero. It also increments Monitoring Cell Sequence Number (MSN), and re-
initializes the BIP field to zero.
As each data cell is segmented, the Seg coprocessor increments the
BLOCK_COUNT number and updates the BIP field.
When the BLOCK_COUNT number reaches the block size specified by
the BLOCK_SIZE field, signifying the end of the PM block, the Seg
coprocessor generates a new forward monitoring PM cell and starts these
processes again.
7.4.3.2 Reassembly of
Forward Monitoring PM
Cells
When the RS8234 receives a forward monitoring PM cell, the Rsm coprocessor
reads the RSM_PM table word pointed to by the PM_INDEX field in the Rsm
VCC Table entry. The location of the RSM_PM Table is above the LECID Table.
The BIPV, TRCC0, and TRCC0+1 fields are written to a special RSM-PM for-
ward monitoring status queue entry. The TUC0 and TUC0+1 fields can be
extracted directly from the RSM_PM cell payload.
When a new buffer is needed, the reassembly coprocessor uses the global
OAM buffer queue if RSM_CTRL1(OAM_QU_EN) is a logic high. Otherwise, it
uses the BFR0 pool identification number in the Rsm VCC Table to point to the
appropriate free buffer queue.
A Rsm status entry is written for each OAM cell reassembled.
The reassembly coprocessor uses the global OAM status queue if the
RSM_CTRL1(OAM_QU_EN) bit is a logic high. Otherwise, it uses the STAT
field in the Rsm VCC Table to determine which status queue to use for that chan-
nel.
7.4.3.3 Reassembly of
Backward Reporting PM
Cells
Backward reporting cells are reassembled in the same manner as non-PM OAM
cells.
7.4.3.4 Turnaround and
Segmentation of
Backward Reporting PM
Cells
For each forward monitoring cell received, the RS8234 also writes the BIPV,
TRCC0, TRCC0+1, TUC0, and TUC0+1 fields to the RS_Queue, for further pro-
cessing by the segmentation coprocessor. The segmentation coprocessor gener-
ates a backward reporting cell.
7.4.3.5 Turnaround of
Backward Reporting PM
Cells ONLY
To enable turnaround of backward reporting PM cells without generation of for-
ward monitoring PM cells, set the segmentation PM_EN bit in the Seg VCC Table
entry to a logic high, set the PM_INDEX, and set the FWD_MON field to zero.
7.4.4 Error Conditions During PM Processing
If OAM cells are not using the global reassembly OAM buffer pool, then the cells
are treated as Single Segment Messages (SSMs) for purposes of the firewall pro-
tection. OAM cells using the global OAM buffer pool do not have per channel
protection.