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3.0 Functional Description
3.5 Reassembly Coprocessor
Bt8230
ATM Segmentation and Reassembly Controller—SAR
N8230DS1F
3.5.12 AAL3/4 CPCS Processing
AAL3/4 processing is used when the AAL_TYPE field in the hash bucket indi-
cates AAL3/4. CPCS header, payload, and trailer are written to memory. The fol-
lowing checks occur before the cell is accepted for further processing:
If the CRC10_EN bit is set to one in the hash bucket, the CRC10 field is
checked. If in error, the cell is discarded and the CRC10_ERR counter at
the top of the hash table is incremented. The CRC polynomial is:
x
10
+ x
9
+ x
5
+ x
4
+ x
1
+ 1.
The MID field value is checked against the number of active MID bits
specified by the MID_BITS field in the hash bucket. If invalid bits are set,
the cell is discarded and the MID_ERR counter at the top the hash bucket
is incremented.
If the ST_EN bit is set to one in the hash bucket, the ST field is checked.
The NEXT_ST field in the VCC table is used for this check. A value of 1
in NEXT_ST field indicates expecting BOM/SSM. A 00 value indicates
expecting Continuation of Message (COM)/EOM. The following errors
are detected:
a.Receive BOM expecting COM/EOM—The current CPCS-PDU is
terminated. A status entry is sent with the ST_ERROR bit set,
CPCS_LENGTH = 0 and the BOM_EOM_ERR counter at the top of the
hash table is incremented. A new CPCS-PDU is started with the current
BOM.
b.Receive SSM expecting COM/EOM—The current CPCS-PDU is ter-
minated. A status entry is sent with the ST_ERROR bit set and
CPCS_LENGTH = 0. The current SSM is processed as a valid CPCS-
PDU. The SSM_COM_ERR counter at the top of the hash table is incre-
mented.
c.Receive COM expecting BOM/SSM—The cell is discarded and the
SSM_COM_ERR counter at the top of the hash table is incremented.
d.Receive EOM expecting BOM/SSM—The cell is discarded and the
BOM_EOM_ERR counter at the top of the hash table is incremented.
If EOM and LI = 63, a status entry is sent with ABORT set and
CPCS_LENGTH = 0.
If the LI_EN bit in the hash bucket is set to one, the LI field is checked.
The following errors are detected:
a.Receive BOM and LI
≠ 44—The cell is discarded and the LI_ERR
counter at the top of the hash table is incremented.
b.Receive COM and LI
≠ 44—The cell is discarded and the current
CPCS-PDU is terminated. A status entry is sent with the LI_ERROR bit
set, CPCS_LENGTH = 0 and the LI_ERR counter at the top of the hash
table is incremented.
c.Receive EOM and (LI < 4) or (LI > 44—The cell is discarded and the
current CPCS-PDU is terminated. A status entry is sent with the
LI_ERROR bit set, CPCS_LENGTH = 0 and the LI_ERR counter at the
top of the hash table is incremented.
d.Receive SSM and (LI < 8) or (LI > 44)—The cell is discarded and the
LI_ERR counter at the top of the hash bucket is incremented.