Released
Datasheet
PM73487 QRT
PMC-Sierra, Inc.
PMC-980618
Issue 3
622 Mbps ATM Traffic Management Device
1 SYSTEM APPLICATIONS
The QRT, together with the QSE, support a wide range of high-performance ATM switching sys-
tems. These systems range in size from 622 Mbps to 160 Gbps. The systems can be developed
such that this scalability is provided with linear cost. Another key feature of the QRT/QSE archi-
tecture is that it is exceptionally fault-tolerant, both in the switch fabric and the UTOPIA inter-
face.
This section contains a quick overview of the QRT and several example applications:
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a stand-alone 622 Mbps switch using a single QRT,
a 5 Gbps switch using QRTs and a QSE,
a 10 Gbps switch using QRTs and QSEs,
a switch architecture using QRTs and QSEs that scales from 5 Gbps to 20 Gbps,
a switch architecture using QRTs and QSEs that scales from 5Gbps to 160 Gbps
1.1 QRT System Overview
The QRT provides 622 Mbps of input and output buffered access to switch fabrics composed of
QSEs (32 x 32 PM73488s). In addition, the QRT supports a stand-alone, purely output-buffered
622 Mbps switch mode. Head-of-line blocking, commonly associated with input buffers, is virtu-
ally eliminated via per-VC receive queues, three types of per-cell switch fabric feedback, and per-
VC cell selection algorithms. The QRT also provides eight separate congestion thresholds, each
with hysteresis, that selectively control AAL5 Early Packet Discard (EPD)/Packet Tail Discard
(PTD), CLP-based cell dropping, and/or EFCI marking. Eight separate maximum thresholds are
also supported. Additional highlights of the QRT include full VPI/VCI header translation, sepa-
rate input and output cell buffers (up to 64K each), Virtual Path Connection (VPC)/Virtual Chan-
nel Connection (VCC) connections, and up to 16K VCs. The QRT provides a bidirectional
connection between a UTOPIA Level 2 interface and 4-nibble wide, 66 MHz switch fabric inter-
faces, as shown in Figure 2 on page 5. A significant switch speed-up factor, up to 1.6 times the
line rate, is used to support full throughput for many switch fabric configurations.
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PMC [ PMC-SIERRA, INC ]
