81
5.0 Reassembly Coprocessor
5.3 CPCS-PDU Processing
RS8234
Datasheet for RS8234 xBR ServiceSAR
N8234DS1B
5.3.2.2 AAL3/4
Additional BOM/SSM
Processing
The RS8234 performs the following additional checks and functions on each
BOM or SSM cell received:
When a BOM cell is received for an AAL3/4 CPCS-PDU (i.e., with ST
field set to b10), the RS8234 checks if the CPI_EN bit in the Rsm AAL3/4
Head VCC table entry is set to a logic high. If so, the CPI field in the
received cell is checked for a zero value. If not a zero value, the RS8234
treats this as an error condition and discards the cell, terminates the current
CPCS-PDU, writes a status queue entry with the CPI_ERROR bit set, and
the CPCS_LENGTH and BD_PNTR fields set to zero. Cells up to and
including the next EOM are discarded.
The RS8234 also checks if the BAH_EN bit in the Rsm AAL3/4 Head
entry is set to a logic high. If so, it checks if the BASIZE field in the
CPCS-PDU header is less than 37 octets, and if so, the RS8234 discards
the current cell, terminates the current CPCS-PDU, and writes a status
queue entry with the BA_ERROR bit set, and the CPCS_LENGTH and
BD_PNTR fields set to zero. Cells up to and including the next EOM are
discarded.
If the CPI and BASIZE fields are correct in the BOM cell, the RS8234
copies the BASIZE and BTAG fields into the VCC table entry for that
MID, and sets the NEXT_ST and NEXT_SN values in the VCC table
entry. It also writes the CPCS-PDU header into the data buffer.
If the LI field in the SAR-PDU > (BASIZE+7), the SAR discards the cell,
terminates the CPCS-PDU, and writes a status queue entry with the
LEN_ERROR bit set and CPCS_LENGTH = zero.
5.3.2.3 AAL3/4
Additional COM
Processing
The RS8234 performs the following additional checks and functions on each
COM cell received:
The RS8234 checks if the sum of the LI fields for the CPCS-PDU are
greater than (BASIZE + 7). If so, the RS8234 discards the cell, terminates
the CPCS-PDU, and writes a status queue entry with the LEN_ERROR bit
set high, CPCS_LENGTH set to zero, and BD_PNTR pointing to the par-
tially reassembled PDU.
5.3.2.4 AAL3/4
Additional EOM/SSM
Processing
Upon termination of a CPCS-PDU, the RS8234 performs the following additional
checks and functions on each EOM or SSM cell received:
The
Length field
in
the CPCS-PDU trailer is written to the
CPCS_LENGTH field of a Rsm status queue entry written for the VCC.
The RS8234 performs a Pad length check to see if the sum of all LIs for
the CPCS-PDU - LENGTH - 8 = [0 to 3] octets. If in error, it sets the
PAD_ERROR bit in the status queue entry.
The RS8234 performs a modulo 32 bit check. If the sum of all LIs for the
CPCS-PDU is not modulo 32 bit, the SAR sets the MOD_ERROR bit in
the status queue entry.
If the Alignment (AL) field in the CPCS-PDU trailer is not all zeros, it sets
the AL_ERROR bit in the status queue entry.
If the BTAG field in the Rsm VCC table entry does not match the ETAG
field in the CPCS-PDU trailer, it sets the TAG_ERROR bit in the status
queue entry.
The RS8234 checks the BAT_EN bit in the AAL3/4 Head VCC table
entry. If BAT_EN is high, it compares the BASIZE field to the Length