cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 173

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

CN8237
ATM OC-12 ServiceSAR Plus with xBR Traffic Management
28237-DSH-001-C
6.2.3.4 CBR Channel
CBR PVC Provisioning
CBR SVC Setup and
CBR Rate Matching
Management
Teardown
The host initializes the segmentation VCC table entry of a CBR VCC. The
SCH_MODE of the VCC must be set to 001 (CBR). Thereafter, the CN8237
ignores further processing based on the SCH_MODE field in the VCC table entry
for CBR VCCs.
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
CN8237 dynamically allocates these cell slots to other channels until the data is
supplied for the CBR VCC.
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.
In reality, the CBR schedule rate of a channel does not exactly match the rate of
its data source. To compensate for this asynchronous data source behavior, the
CN8237 provides a rate-matching mechanism for use when CBR traffic is
mapped to a Virtual FIFO buffer. (This method is needed only for Virtual FIFO
buffers. For VCCs that are not Virtual FIFO buffers, the cell transmission is
skipped automatically if there is no data available.)
directs the CN8237 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 CN8237 encounters a CBR
slot for this VCC, it does not transmit data on that VCC. Then, the CN8237
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 buffer, the host
With this method, the host effectively synchronizes the CN8237’s scheduled
Mindspeed Technologies
™
6.2 xBR Cell Scheduler Functional Description
6.0 Traffic Management
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