cn8236 Mindspeed Technologies, cn8236 Datasheet - Page 120

• Manufacturer Part Number: cn8236
• Description: Atm Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

5.0 Reassembly Coprocessor
5.3 CPCS-PDU Processing
5.3.1 AAL5 Processing
Figure 5-8. AAL5 EOM Cell Processing—Fields to Status Queue
5-10
. . .
5.3.1.1 AAL5 COM
5.3.1.2 AAL5 EOM
ATM Cells
AAL5 PDU
Processing
Processing
(User Data)
Except for the EOM cell, all of the data within AAL5 cell payloads is user data.
The reassembly coprocessor writes all user data to memory as described in
Section
delineates the end of an AAL5 PDU.
During reassembly of the PDU, the reassembly coprocessor calculates a CRC-32
value on the received AAL5 PDU, and counts the length of the PDU. The CRC-32
value is collected in an accumulator, and the LENGTH value is collected in a
Length Counter. After each received cell is processed, the reassembly coprocessor
writes the CRC-32 and LENGTH values to the reassembly VCC state table entry
for that channel.
During reassembly of the AAL5 PDU, certain bytes of the PDU other than user
data are written to a status queue entry for that PDU. The RSM coprocessor writes
these specific fields to the status queue entry:
When the EOM cell is processed, the reassembly coprocessor performs the
following checks:
• UU information
• CPI field
• LENGTH field
Figure 5-8
• If the LENGTH field in the trailer of the AAL5 PDU is 0, the reassembly
• Compares the calculated CRCREM value to the CRC-32 value in the
• Compares the value collected in the Length Counter to the value in the
• If the CPI field in the AAL5 trailer is not 0, the CPI_ERROR bit in the
• All of the AAL5 trailer information is also written into the end of the PDU
coprocessor sets the ABORT bit in the status queue entry to a logic high.
trailer of the AAL5 PDU. If different, the reassembly coprocessor sets the
CRC_ERROR bit in the status queue entry to a logic high.
LENGTH field in the trailer of the AAL5 PDU. If the number of PAD
bytes is less than 0 or greater than the 47 the reassembly coprocessor sets,
the PAD_ERROR bit in the status queue entry to a logic high.
status queue entry is set to a logic high.
buffer(s) in memory.
5.4. The EOM cell contains both user data and CPCS-PDU overhead, and
Mindspeed Technologies
. . .
. . .
illustrates these process functions.
EOM Cell
PAD UU CPI LENGTH CRC-32
ATM ServiceSAR Plus with xBR Traffic Management
™
28236-DSH-001-B
Queue
Status
Entry
CN8236
8236_026