RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
9.2.1.3.2.1 Header Construction
The entire header is fixed per queue. Headers are maintained in the memory,
one per queue. These headers include a Header Error Check (HEC) character
for the fifth byte. The queue should be deactivated during header replacement to
prevent cells from being constructed with incorrect header values. A queue can
be paused by setting the SUPPRESS_TRANSMISSION bit in TX_CONFIG
register. Emissions are still scheduled, just the transmissions are suppressed.
For any cells that are suppressed, the T_SUPPRESSED_CELL_CNT is
incremented.
9.2.1.3.2.2 Payload Construction
Payload construction is the most complex task the TALP circuit performs. The
AAL1 requirements define much of the process, which is as follows:
1) The first byte of the payload is provided by a lookup into the T_QUEUE_TBL.
This first byte consists of the CSI bit, a 3-bit sequence number, and a 4-bit
sequence number protection field. The CSI bit is set depending on SRTS and
pointer requirements. The sequence number is incremented every time a new
cell is sent for the same VPI/VCI. If the queue has been configured for AAL0
mode, this step is not done and an additional data byte is loaded instead.
2) If the line is in one of the two structured modes, a structure pointer is needed
in one of the even-numbered cells. The TALP inserts structure pointers according
to the following rules:
• Only one pointer is inserted in each 8-cell sequence.
• A pointer is inserted in the first possible even-numbered cell of every 8-cell
sequence.
• A pointer value of 0 is inserted when the structure starts in the byte directly
after the pointer itself.
• A pointer value of 93 is inserted when the end of the structure coincides with
the end of the 93-octet block of AAL-user information.
• A dummy pointer value of 127 is inserted in cell number six if no start-of-
structure or end-of-structure occurs within the 8-cell sequence.
3) This algorithm supplies a constant number of structure pointers and, therefore,
data bytes, regardless of the structure size. The pointer is inserted in the seventh
byte location of the cell. To force the TALP to build a structure consisting of a
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