Cisco 12012 Gigabit Switch Router Switch Fabric Cards Replacement Instructions 3
Product Overview
Clock and Scheduler Card
The Cisco 12012 requires that one clock and scheduler card be installed in the lower card cage. You
can add one additional clock and scheduler card for redundancy and to increase the amount of data
able to be transferred between line cards. The clock and scheduler card contains the following
functionality:
• System clock—Sent to all line cards, RP, and switch fabric cards. The system clock synchronizes
data transfers between line cards or line cards and the RP through the switch fabric. In systems
with redundant clock and scheduler cards, the two system clocks are synchronized. Should one
system clock fail, the other clock takes over.
• Scheduler—Handles requests from the line cards for access to the switch fabric. When the
scheduler receives a request from a line card for switch fabric access, the scheduler determines
when to allow the line card access to the switch fabric.
• Switch fabric—The circuitry that carries the user traffic between line cards or between the RP
and a line card. The switch fabric on the clock and scheduler card is identical to the switch fabric
on the switch fabric card.
Note In a system configured with only one clock and scheduler card, the clock and scheduler card
is installed in the second slot from the top in the lower card cage.
Switch Fabric Card
The switch fabric card contains only the switch fabric circuitry that carries the user traffic between
line cards or between the RP and the line cards. The card receives scheduling information and the
system clock from the clock and scheduler card. The card is keyed to occupy slots 2, 3, and 4 (lower
three slots) in the lower card cage. The system can run without any switch fabric cards installed.
However, if you want to maximize the bandwidth and switching capacity of the system, you must
install three switch fabric cards in the lower card cage.
