cn8236 Mindspeed Technologies, cn8236 Datasheet - Page 186

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

6.0 Traffic Management
6.2 xBR Cell Scheduler Functional Description
6-18
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 must be set to 001 (CBR). Thereafter, the CN8236
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
CN8236 dynamically allocates 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 does not exactly match the rate of
its data source. To compensate for this asynchronous data source behavior, the
CN8236 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 CN8236 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 CN8236 encounters a CBR
slot for this VCC, it does not transmit data on that VCC. Then, the CN8236
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 CN8236’s scheduled
Mindspeed Technologies
ATM ServiceSAR Plus with xBR Traffic Management
™
28236-DSH-001-B
CN8236