RS8234 Mindspeed Technologies, RS8234 Datasheet - Page 190

• Manufacturer Part Number: RS8234
• Description: Atm Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

6.0 Traffic Management
6.3 ABR Flow Control Manager
Figure 6-18. Backward_RM Flow Control, Block Diagram
6-30
6.3.7.3 Backward RM
RSM/SEG
ABR Decision
Queue
Instruction Table
Cell Flow Control
ABR Exponent
Templates
ABR Rate
Table
The ABR Rate Decision Table consists of many indexed entries. Each of these
entries is called an ABR Rate Decision Block or ARDB. Each ARDB represents a
possible transmission rate for an ABR VCC. The rate of an ARDB is a
monotonically increasing function of the index of the block.
storing its current ARDB index in the RATE_INDEX field of the SCH_STATE
VCC structure. This RATE_INDEX uniquely identifies the current transmission
rate of the VCC. Figure 6-18 illustrates a block diagram of Backward RM flow
control.
algorithm adjusts the state of a connection by a relative rate (RR) algorithm, in
response to the CI and NI bits. The second algorithm allows the network to
explicitly request a transmission rate in the ER RM cell field. Each of these
algorithms produces a candidate rate. The Source must adjust its rate to be less
than or equal to the lesser of these two candidates.
parameters into rate index space. Since rate indexes are a monotonically
increasing function of rate, the RS8234 selects the candidate with the lowest rate
index.
This algorithm can adjust the rate relative to the current rate. The adjusted rate
relates to the current rate by a constant multiplicative decrease or additive
increase. Specifically, the adjusted rate increases by RIF*PCR or decreases by
RDF*ACR. These values are pre-calculated and used to formulate a RS8234
ABR Rate Instruction Table, avoiding real time math.
Flow Control
Manager
The RS8234 tracks the state of each ABR connection’s transmission rate by
Backward RM cells deliver stimulus for two flow control algorithms. The first
The RS8234 computes both rate candidates by first mapping all rate
For the RR algorithm, the conversion is embedded in the ARDBs themselves.
ABR
(RATE_INDEX)
SCH_STATE
Mindspeed Technologies
Table Entry
SEG VCC
(CI, NI & ER Fields)
Scheduler
SAR
Cell
Rate
Decision
ATM ServiceSAR Plus with xBR Traffic Management
Coprocessor
Segmentation
Reassembly
Coprocessor
™
BACKWARD_RM
Cell Stream
ABR
UNI
Destination
Network +
28234-DSH-001-B
ATM
RS8234
100074_057