cn8236 Mindspeed Technologies, cn8236 Datasheet - Page 188

• 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
6.2.5 UBR Traffic
6.2.6 xBR Tunnels (Pipes)
6-20
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 correspond
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
A CBR tunnel occupies schedule table slots in the same manner as a CBR VCC.
However, instead of serving one VCC, from one to four priority levels are served.
The VCCs within a CBR tunnel can be UBR, VBR (VBR1 or VBR2), and/or
ABR traffic. In the case of a UBR priority in a tunnel, the VCCs of the served
priority level are serviced in round-robin order. For any VBR/ABR priorities in a
tunnel, each VCC is shaped to its GCRA parameters within the CBR tunnel.
NOTE:
for that tunnel is reserved in the schedule table as schedule slots. The one-to-four
priority levels assigned to that tunnel are named at this time, and are written to the
PRI3, PRI2, PRI1, and PRI0 fields in the CBR_TUN_ID field for the schedule
slots reserved. PRI3 should specify the highest priority level for that tunnel, down
to PRI0 as the lowest assigned priority level for that tunnel. The scheduler
services the highest priority level that has data available on that priority queue at
each point a schedule slot for that tunnel becomes active. This serves as a
secondary shaping of the traffic assigned to these tunnel priorities. Any one
priority level can be assigned to only one CBR tunnel, and must not be assigned
as a priority to more than one tunnel. Additionally, all priority levels used within a
The minimum rate for VBR channels is R
To limit the bandwidth that a UBR priority consumes, use a CBR tunnel in
When the user establishes a CBR tunnel, the user-defined transmit bandwidth
((# VBR VCCs at same-or-higher priority)
The format of a CBR tunnel schedule table slot is not backward-
compatible with the CBR tunnel format used in the Bt8233 SAR.
Mindspeed Technologies
Section
ATM ServiceSAR Plus with xBR Traffic Management
6.2.8.
™
+
TX_FIFO_LEN) (line rate in cells sec)
max
/
(TBL_SIZE –1).
max
/
(TBL_SIZE – n),
28236-DSH-001-B
CN8236