
RS8234
7.0 OAM Functions
ATM ServiceSAR Plus with xBR Traffic Management
7.4 PM Processing
N8234DSC
PRELIMINARY
7-11
7.4.3 PM Operation
PM processing operates automatically on any channel until stopped by clearing
the PM_EN fields in the Seg VCC Table entry and the Rsm VCC Table entry.
PM-OAM cells are not included in the NRM cell count, as part of ER
processing. See Chapter 6 for details.
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
forward 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
channel.
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
processing by the segmentation coprocessor. The segmentation coprocessor
generates 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
forward 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.