RS8234EBGC Mindspeed Technologies, RS8234EBGC Datasheet - Page 181

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

RS8234
ATM ServiceSAR Plus with xBR Traffic Management
6.2.7 Guaranteed Frame Rate
6.2.8 PCR Control for Priority Queues
28234-DSH-001-B
GFR is a new service category defined by the ATM Forum to provide an MCR
QoS guarantee for AAL5 CPCS-PDUs (or “frames”) not exceeding a specified
frame length. This class of service is designed specifically to use the UBR service
category. A GFR service connection is thus treated as UBR with a guaranteed
MCR.
both the VBR1 scheduling procedure (for the MCR rate value) and a UBR
priority queue, thereby providing fair sharing for all GFR connections to excess
bandwidth. The VBR1 queue priority (the PRI field in the SEG VCC Table entry)
should be set to a higher priority than the UBR queue (the GFR_PRI field in the
SEG VCC table entry). The priority level entered in the GFR_PRI field can only
be one of the lower eight scheduling priorities. This establishes the condition
where those GFR connections sharing the same GFR_PRI would fair-share any
excess bandwidth above the MCR limits. Call control must be sure not to
oversubscribe MCR on GFR channels and other rate-guaranteed services.
mechanism to trigger an increase in the scheduling priority by one priority level,
if the transmit rate on that channel falls below its specified MCR. This is done
using the MCRLIM_IDX field in that VCC’s SCH_STATE entry in the SEG
VCC Table entry. MCRLIM_IDX is an 8-bit index into a table containing 256
entries (each formatted as described in
values, and each indicating a trigger point for an increase in the VCC’s priority for
that scheduled slot.
user can accomplish this by setting each of the values in the GFR MCR Limit
bucket table entries as follows:
An additional level of traffic shaping can be established on GFR-UBR priority
queues by shaping to a specified PCR. (See
The RS8234 provides an optional method of creating tunnels (i.e., of limiting the
bandwidth of a group of channels), by allowing the user to assign a PCR to a
scheduling priority queue, so that the aggregate of the rates of the channels
assigned to that priority queue will not be greater than the PCR assigned. This can
be done for UBR, VBR, ABR and UBR-GFR traffic classes.
than line rate. The queues to be shaped are identified using the QPCR_ENAx bits
in the SCH_PRI and SCH_PRI_2 registers. The associated PCR for each queue
thus enabled is specified in one of the two PCR_QUE_INTxx registers. These
PCR values are stored as schedule table intervals. QPCR_INT3 maps to the
highest priority queue that is enabled for PCR shaping, QPCR_INT2 to the next
highest priority PCR shaped queue, and so on. If only one priority queue is
enabled for PCR shaping, it will be shaped using the QPCR_INT3 value; if two
priority queues are enabled for PCR shaping, QPCR_INT3 and QPCR_INT2 will
be used; and so on.
The RS8234 implements GFR by scheduling/shaping the connections using
The RS8234 helps guarantee MCR on a GFR channel by providing a
To disable this priority bumping, set MCR_LIMIT to its maximum value. The
1.
2.
3.
A maximum of four of the sixteen priority queues can be shaped to a PCR less
Set NONZERO bits to 1.
Set MCR_EXP fields to decimal value of 31 (i.e., all-ones).
Set MCR_MAN fields to decimal value of 511 (i.e., all-ones).
Mindspeed Technologies
Table
™
6.2 xBR Cell Scheduler Functional Description
Section
6-19), each containing MCR limit
6.2.8.)
6.0 Traffic Management
6-21