RS8234EBGC Mindspeed Technologies, RS8234EBGC Datasheet - Page 175

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

RS8234
ATM ServiceSAR Plus with xBR Traffic Management
28234-DSH-001-B
6.2.3.4 CBR Channel
Management
The host initializes the segmentation VCC Table entry of a CBR VCC. The
SCH_MODE of the VCC should be set to 001 (CBR). Thereafter, the RS8234
ignores further processing based on the SCH_MODE field in the VCC Table
entry for CBR VCCs.
CBR PVC Provisioning
Once a Schedule Table has been created, the system assigns specific cell slots to
any CBR provisioned virtual connections (PVCs). This process takes place before
the segmentation process is initiated. Once segmentation has begun, the RS8234
will dynamically allocate these cell slots to other channels until the data is
supplied for the CBR VCC.
CBR SVC Setup and Teardown
It is also possible to set up and tear down CBR switched virtual connections
(SVCs) without disrupting ongoing segmentation. The user simply configures a
new VCC Table entry. Once the VCC is initialized, the host assigns schedule slots
to the VCC according to its rate. The host then submits data as with any
segmentation VCC.
CBR Rate Matching
In reality, the CBR schedule rate of a channel will not exactly match the rate of its
data source. To compensate for this asynchronous data source behavior, the
RS8234 provides a rate matching mechanism for use when CBR traffic is mapped
to a Virtual FIFO. (This method is needed only for Virtual FIFOs. For VCCs that
are not Virtual FIFOs, the cell transmission is skipped automatically if there is no
data available.)
RS8234 to skip one cell transmission opportunity whenever data is unavailable.
The host requests this rate matching adjustment by setting the SCH_OPT bit of
the CBR channel. The next time the RS8234 encounters a CBR slot for this VCC,
it will not transmit data on that VCC. Then the RS8234 indicates to the host that a
slot has been skipped by clearing the SCH_OPT bit.
rate to the external data source rate. The host must configure the CBR VCC rate
slightly higher than the actual rate of the data source. Skipping cell transmission
slots then compensates for the rate differential.
For an individual CBR channel mapped to a Virtual FIFO, the host directs the
With this method, the host effectively synchronizes the RS8234’s scheduled
Mindspeed Technologies
™
6.2 xBR Cell Scheduler Functional Description
6.0 Traffic Management
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