cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 186

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

6.0 Traffic Management
6.3 ABR Flow Control Manager
6-30
APPLICATION EXAMPLE: Cell Decision Table for Nrm=32
The figure below, shows a typical Cell Decision table. The anchor of the table, the FWD_INDEX
ACDB, is located at index 100 of the ABR Decision table. Whenever a Forward RM cell is sent, this
ARCB serves as the reset point for the decision state machine. When CELL_INDEX =
FWD_INDEX, a steady state ABR channel transmits a Backward RM cell and advances the
CELL_INDEX. The diagram shows the next ACDB (101) in more detail. It contains the 16 Cell Type
Actions (for example, BRM = Send Backward RM). At the next cell transmission opportunity,
the ABR Flow Control Manager state machine selects a cell type by indexing into the ACDB
according to the ACDV. In this case, the only condition present is RUN=1, so ACDV = 0001b.
Cell Type Action Index 1 is selected. For this ACDB, Cell Type Action 1 is DATA or Send Data Cell.
Therefore, the CN8237 transmits a user data cell.
transmits a Forward RM Cell under all circumstances. Therefore, the CN8237 resets the CELL_INDEX
for this VCC to FWD_INDEX = 100, when it reaches this ACDB.
Forward RM cell, and the sequence would continue from the FWD_INDEX.
In this example, the host should initialize CELL_INDEX to 131. The CN8237 would transmit a
Run-time Operation
In steady state, CELL_INDEX is incremented until it reaches ACDB 131. This ACDB
Table 6-5. ABR Cell Type Decision Vector (ACDV)
Each time an ABR cell-transmit opportunity arises, the CN8237 makes a cell
decision. The SAR retrieves CELL_INDEX from SCH_STATE and chooses a
Cell Type Action location within the current ACDB.
conditions which are used to form this vector. The presence of a condition sets the
vector bit to a 1.
an in-rate Forward RM cell is transmitted, FWD_INDEX is copied to
CELL_INDEX; otherwise, CELL_INDEX is incremented by one
(CELL_INDEX++). Therefore, the number of blocks in a Decision table is
bounded by the maximum number of cell decisions made between transmitted
Forward RM cells, typically Nrm.
3
2
1
0
Bit
The SAR updates the CELL_INDEX field after each cell decision is made. If
TRM_EXP
TA_PND
TA_XMIT
RUN
Mindspeed Technologies
Name
Time since last forward RM transmitted
TA_PND bit set in VCC table entry
TA_XMIT bit set in VCC table entry
RUN bit set in VCC table entry
ATM OC-12 ServiceSAR Plus with xBR Traffic Management
™
Description
Table 6-5
TRM
28237-DSH-001-C
shows the four
CN8237