PM73487 datasheet(43/251 Pages) PMC

43 / 251 page

PM73487 QRT

PMC-Sierra, Inc.

PMC-980618

Issue 3

622 Mbps ATM Traffic Management Device

Released

Datasheet

Figure 37 shows the operation of EFCI.

The congestion limits are kept in an exponential form. The interpretation of the limits is the same

for all measurements, except the device limit. For the other measurements, the value of “0” causes

the measurement to always find congestion. The value of “1” may not be used. The value of F

causes congestion to be found for the limit when the queue depth is 31744. This allows a 15-bit

value to be used to store the state of each measurement except the device measurement, which has

a 16-bit value.

2.5.5

Receive Queue Service Algorithm

Each switch fabric cell time, the receive queue controller selects up to four cells for transmission

to the switch fabric. The controller supports per-channel (per-VC) queues with 64 SCs. The con-

troller addresses the following issues: QoS, Cell Delay Variation (CDV) minimization, Minimum

Cell Rate (MCR) guarantees, and fairness maximization. The flexibility of the controller ensures

that VCs receive their expected bandwidth in a timely fashion depending upon their traffic

requirements.

Figure 37. EFCI Operation

Figure 38. Steps to Send a Cell to the Fabric

EFCI Codepoints Set

From Here

To Here

Time

Queue

Depth

Congestion Threshold

÷ 2

Run Queue Service Algorithm to

determine Service Class (SC)

Read from ring to

determine channel

Find pointer to cell from

channel linked list

Fetch cell

Send cell to fabric

Update structures with

results of transmission

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