cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 175

• 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
6.2.5 UBR Traffic
28237-DSH-001-C
6.2.4.7 Real-Time VBR
6.2.4.6 Rate Selection
6.2.4.5 CLP-Based
and CDV
Buckets
The third option allows both buckets to apply to CLP = 0 cells. CLP=0 means
high priority cells; CLP = 1 means cells are subject to discard. CLP = 1 cells are
scheduled from the second bucket only. Therefore, the second bucket corresponds
to PCR. This controls the PCR of the total cell stream, but only controls the SCR
of CLP = 0 cells. The user enables this scheme by setting the SCH_MODE bits to
110 (VBRC—also called VBR3).
The I and L parameters of the GCRA algorithm represent cell slots in the
schedule table. Therefore, the VBR channels have the same maximum rate
available as the CBR channels. Since VBR channels are internally scheduled by
the Cell Scheduler based on that channel’s I parameter, a floating point value, they
are not constrained to repeat at some n integer value of R
Thus, VBR channels have a much finer rate granularity.
Real-time VBR traffic should be assigned the highest scheduling priority to
minimize cell delay variation. The worst-case CDV for rt-VBR traffic is
calculated as
The remaining priority levels not already assigned to ABR, VBR, or CBR tunnel
traffic are scheduled as UBR traffic. All UBR channels within a priority are
scheduled on a round-robin basis.
that priority level. Another method of limiting the bandwidth that a UBR priority
consumes is described in
The minimum rate for VBR channels is R
To limit the bandwidth that a UBR priority consumes, use a CBR tunnel in
Mindspeed Technologies
((# VBR VCCs at same-or-higher priority)+TX_FIFO_LEN) /
(line rate in cells/sec).
Section
6.2.8.
™
6.2 xBR Cell Scheduler Functional Description
max
/
(TBL_SIZE –1).
max
6.0 Traffic Management
/
(TBL_SIZE – n),
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