PM7375-SC datasheet(67/430 Pages) PMC

67 / 430 page

PM7375 LASAR-155

DATA SHEET

PMC-931127

ISSUE 6

LOCAL ATM SAR & PHYSICAL LAYER

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

9.7

Transmit ATM Traffic Shaper

The Transmit ATM Traffic Shaper (TATS) block provides for Variable Bit Rate (VBR)

traffic shaping. VBR traffic shaping requires each VC to conform to peak cell rate

enforcement, using peak cell rate queues, and sustainable cell rate enforcement,

using peak cell rate queues coupled with token bucket averaging. In addition a

proprietary Credit Based Rate Control (CBRC) algorithm can be applied to the

Variable Bit Rate (VBR) VCs.

9.7.1 Rate Queue Structures

The TATS block provides for eight peak cell rate queues arranged as a group of four

high priority queues and a group of four low priority queues. As part of the

provisioning process, a VC must be associated with one of the eight rate queues.

Once a VC is provisioned, packets supplied by the PCI Host are attached to the

associated rate queue as conceptually shown below. Successive packets of an

existing VC are linked to the existing packets waiting to be transmitted over the VC

in question.

To enforce fairness, rate queues are serviced in a round-robin fashion on a per

queue group basis. High priority queues are serviced in a round-robin manner

before the low priority queues. If the high priority queues consume all the available

link bandwidth, the low priority queues are allowed to starve. An indication is

provided to indicate if any queue has experienced a starvation condition. Servicing

of low priority queues is allowed to be pre-empted by high priority queues. Once the

TATS begins to service a high priority queue , the queue will be completely serviced

before another queue is serviced. For both low and high priority queues, VCs on the

same queue are serviced on a round-robin fashion.

PM7375-SC Datasheet(PDF) 67 Page - PMC-Sierra, Inc