RS8234EBGC Mindspeed Technologies, RS8234EBGC Datasheet - Page 185

• Manufacturer Part Number: RS8234EBGC
• Description: RS8234EBGC ATM XBR SAR
• Manufacturer: Mindspeed Technologies

RS8234
ATM ServiceSAR Plus with xBR Traffic Management
6.3.5 ABR Templates
6.3.6 Cell Type Decisions
28234-DSH-001-B
6.3.6.1 In-rate Cell
Streams
The ABR Templates reside in SAR shared memory in a region referred to as the
ABR Instruction Table. The ABR Instruction Table contains one or more
templates. Individual VCCs are assigned to a single template. Each template
supports a group of VCCs. The key parameters contained in and controlled by the
ABR Templates are: PCR, Initial Cell Rate (ICR), MCR, RIF, RDF, and Nrm.
or from fields in the SCH_STATE portion of the SEG VCC Table entry for each
connection, thus giving either per-template or per-connection control of MCR and
ICR. This choice is globally set using the ADV_ABR_TEMPL bit in the
SEG_CTRL register.
RS8234 as a complete microcoded state machine.
Rate Decision Table and an Exponent Table.
the transmitted in-rate cell stream.
state includes several vectors to other states, corresponding to different rates.
When an event forces a rate decision, the RS8234 decides which vector to follow
based on network stimulus (CI/NI), ER decisions, or internal timer/counter
expirations (ADTF and Crm).
function. This function maps a TM 4.1 floating point rate representation (in
particular, the RM cell Explicit Rate field) to a Rate Decision Table index. The
Exponent Table is indexed by the Explicit Rate exponent. This mapping function
normalizes the ER field rate to the CI/NI state-based rate decision. Once
normalized, a rate can be chosen based on the minimum of the two rates.
Since every ABR connection in a network is full duplex, the RS8234 is a Source
and a Destination for each VCC. The RS8234 multiplexes user data cells,
Forward RM cells, and Backward RM cells into the in-rate ABR cell stream.
TM 4.1 Source Behaviors specify rules for the in-rate cell stream.
transmits one Forward RM cell. A Backward RM cell follows. Finally, the Source
sends Nrm user data cells. At steady state, this sequence would be repeated with a
Forward RM cell marking the beginning of each sequence.
The user has the choice of defining MCR and ICR from the ABR Templates
These ABR Templates are furnished by Mindspeed, and are downloaded to the
Three components constitute a complete template: a Cell Decision Table, a
The RS8234 uses the Cell Decision Table to select a cell type for insertion into
The Rate Decision Table maps ABR cell stream rates to logical states. Each
The Exponent Table contains parameters for a piece-wise linear mapping
Figure 6-15 shows the desired result of the specification. First, the Source
Mindspeed Technologies
™
6.3 ABR Flow Control Manager
6.0 Traffic Management
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