Overview of the Cisco 12008
In a redundant CSC configuration, the phase of the master clock generator on one card is synchronized with that of the other card. If either clock drifts, the master clock generators on both cards remain tightly aligned.
Should one of the CSCs fail, the phase lock between the two master clock sources is aborted within nanoseconds, enabling the surviving CSC clock to remain stable and take over master clock duties.
•Frame synchronization
In a redundant CSC configuration, either CSC can adopt the frame synchronization phase of the other to ensure phase alignment. The line cards can switch between frame synchronization masters without disruption.
If the frame synchronization function on one CSC fails, cutover to the surviving frame synchronization generator on the other card occurs within nanoseconds, sustaining system operations.
•Central switch allocator and
Switch arbitration begins with a set of requests from line cards to send data through the router’s switch fabric. The scheduler plans a set of paths through the switch fabric to carry as much data as possible per unit of time. At the next available time unit, the request to send data is granted, and the data is sent to its destination. The next round of switch arbitration (scheduling) then begins.
The scheduler also sends switch fabric control information to each switch plane to create appropriate data paths through the switch fabric. When the new data paths are configured into the switch fabric, data begins to flow toward the destination line card(s).
The central switch allocator and scheduler accepts data transport requests from all line cards (including the RP), generates grants (accepted data transport requests), and drives all planes of the router’s switch fabric.
•Single plane switch
