cn8236 Mindspeed Technologies, cn8236 Datasheet - Page 201

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

CN8236
ATM ServiceSAR Plus with xBR Traffic Management
Figure 6-18. Backward_RM Flow Control, Block Diagram
28236-DSH-001-B
RSM/SEG
ABR Decision
Queue
Instruction Table
ABR Exponent
Templates
ABR Rate
Table
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 CN8236 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 CN8236
ABR Rate Instruction table, avoiding real time math.
responses to the relative rate elements in backward RM cells. The CN8236 uses
the CI/NI bits to choose an ARDB candidate from one of these four vectors. For
instance, if CI is set, the VCC must reduce its ACR by (ACR x RDF). The vectors
in the ARDB that is chosen when CI is set point to ARDBs whose corresponding
rates are less than [ACR – (ACR x RDF)]. The CN8236 recognizes the ARDB
indicated by the chosen vector, as the RR rate index candidate.
Flow Control
Manager
Backward RM cells deliver stimulus for two flow control algorithms. The first
The CN8236 computes both rate candidates by first mapping all rate
For the RR algorithm, the conversion is embedded in the ARDBs themselves.
Each ARDB contains vectors to eight other ARDBs. Four of these vectors are
Figure 6-19
ABR
(RATE_INDEX)
SCH_STATE
Mindspeed Technologies
Table Entry
SEG VCC
(CI, NI & ER Fields)
illustrates the RR Rate_INDEX candidate selection.
Scheduler
SAR
Cell
Rate
Decision
Coprocessor
Segmentation
Reassembly
Coprocessor
™
BACKWARD_RM
Cell Stream
ABR
UNI
6.3 ABR Flow Control Manager
6.0 Traffic Management
Destination
Network +
ATM
8236_050
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