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Cisco 12006 and Cisco 12406 Router Installation and Configuration Guide
OL-11497-03
Chapter 1 Product Overview
Maintenance Bus
Maintenance Bus
The Cisco 12006 and Cisco 12406 router maintenance bus and MBus modules
manage the maintenance functions of the system. The MBus is integrated into the
backplane and consists of two separate buses, providing MBus redundancy.
Both MBus networks are linked to all the following items:
• Route processor and line cards
• CSCs, SFCs, and alarm cards
• Power modules
• Blower module
The MBus module located on each component communicates over the MBus and
is powered by DC voltage directly from the alarm card. The MBus performs the
functions of power-up/down control for each component, component (device)
discovery, code download, diagnostics, and environmental monitoring and
alarms.

Power-Up/Down Control

Each MBus module directly controls the DC-DC converters on the component on
which it is mounted, based on commands the component receives from its
on-board EPROM and from the RP. Each MBus module is tied directly to DC
voltage from the alarm card.
When power is applied to the router, all MBus modules immediately power up.
The MBus modules on the RP and CSC immediately turn on the DC-DC
converter, powering up the respective card. The line card MBus module waits to
power up the line card until it receives a command from the RP.

Device Discovery

The RP uses the MBus to detect the system configuration. The RP sends a
message over the MBus requesting identity information from all installed devices.
The responses provide component type, as well as slot numbers for the line cards,
CSCs, SFCs, and alarm cards.