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Cisco ASR 9000 Series Aggregation Services Router Overview and Reference Guide
OL-17501-09
Chapter 2 Functional Description
Route Processor Card
Figure 2-10 shows the Cisco ASR 9922 Router switch fabric.
Figure 2-10 Cisco ASR 9922 Router Switch Fabric
Unicast Traffic
Unicast traffic through the switch is managed by a VOQ scheduler chip. The VOQ scheduler ensures that
a buffer is available at the egress of the switch to receive a packet before the packet can be sent into the
switch. This mechanism ensures that all ingress line cards have fair access to an egress card, no matter
how congested that egress card may be.
The VOQ mechanism is an overlay, separate from the switch fabric itself. VOQ arbitration does not
directly control the switch fabric, but ensures that traffic presented to the switch will ultimately have a
place to go when it exits the switch, preventing congestion in the fabric.
The VOQ scheduler is also one-for-one redundant, with one VOQ scheduler chip on each of the two
redundant RSP/RP cards.
Multicast Traffic
Multicast traffic is replicated in the switch fabric. For multicast (including unicast floods), the
Cisco ASR 9000 Series Routers replicate the packet as necessary at the divergence points inside the
system, so that the multicast packets can replicate efficiently without having to burden any particular
path with multiple copies of the same packet.