cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 185

• Manufacturer Part Number: cn8237
• Description: Atm Oc-12 Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

CN8237
ATM OC-12 ServiceSAR Plus with xBR Traffic Management
Figure 6-16. Cell Type Interleaving on ABR-ER Cell Stream
28237-DSH-001-C
Initialization Instructions
6.3.6.2 ABR Cell
Decisions
(SCH_STATE)
State Table
SEG VCC
specification on cell stream interleaving. This Cell Type Decision algorithm
makes on-the-fly decisions concerning which type of cell to send, based on the
current state of the connection.
algorithm. The ABR Flow Control Manager chooses a cell type based on a Cell
Decision table and the VCC state. The segmentation coprocessor then formats the
appropriate cell type and sends it on the ABR in-rate cell stream.
NOTE:
the user can modify it to optimize performance or react to changes in the ABR
specification. Furthermore, multiple tables allow groups of VCCs to be tuned for
different network policies.
The Cell Decision Tables reside in SAR SEG-shared memory as a segment of the
Flow Control Manager’s ABR Instruction table. Each entry of a table is an ABR
Cell Decision Block (ACDB). Each ACDB contains sixteen Cell Type Actions.
Cell Type Actions result in one of four decisions: send in-rate Forward RM cell,
send in-rate Backward RM cell, send user data cell, or no action. A Cell Type
Action is chosen by a 4-bit ABR Cell Type Decision Vector (ACDV). The four
bits of the ACDV correspond to four current ABR VCC conditions.
At system initialization, the host loads one or more Cell Decision Tables into
SAR SEG-shared memory. Mindspeed provides standard Cell Decision Tables.
The system designer uses either these or customized templates.
at connection setup time. The first field, CELL_INDEX, tracks the current
ACDB position of the VCC. Source Behavior #2 specifies that the first in-rate
cell on a VCC is a Forward RM cell. Therefore, CELL_INDEX should be
initialized to an ACDB position which always decides to send a Forward RM cell.
The second field, FWD_INDEX, provides a reset point for the in-rate cell stream
sequence. Whenever the CN8237 transmits an in-rate Forward RM cell, it copies
FWD_INDEX to CELL_INDEX.
The CN8237 provides a programmable mechanism to comply with TM 4.1’s
Since the Cell Decision table template resides in SAR SEG-shared memory,
To assign an ABR VCC to a table, the host initializes two SCH_STATE fields
Data Cell
Forward RM
Backward RM
None
The ABR Flow Control Manager may choose to send no cell. This occurs
when the VCC has no user data to segment.
Mindspeed Technologies
Manager
Control
Flow
ABR
Cell Type
Action
Figure 6-16
Decision
Table
Cell
™
ABR-ER Cell Stream
shows a block diagram of the
6.3 ABR Flow Control Manager
6.0 Traffic Management
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