System Overview
system can function at the higher speed indefinite ly. Form orein formation,
see Cooling System on page 39.
Host module (Routing Engine and MCSf unctioningtogether)—The router
can have one or two host modules. If two host modules are installed,one
(the master) is active and the other is in standby mode. If the master host
module (or either ofits components) is removed from the chassis,the standby
host module becomes active. The Routing Engine andMCS must reside in
adjacent slots and be fully operationalfor the host module to function. For
more information, see Host Modul e on page 22.
PCG—The router has two PCGs. Both PCGs send their clock signals to the
other Packet Forwarding Engine components, along with a signal that indicates
which clock is the master.If one PCG fails, the other PCG becomes the master
system clock. For more information, see“Packet Forwarding Engine Clock
Generators (PCGs)”on page 18.
Power supply—The router has two load-sharing, fully redundant power
supplies to distributeDC power to the other components. If one power
supply fails,the second power supply can provide full powerto the router’s
components indefinitely. For more information, see Power System on page 35.
SFM—The router can haveup to four interconnected SFMs. If one SFM fails,
the switching and forwardingfunctions of the failed module are distributed
among the remaining SFMs. Totalbandwidth is reduced by 1/n,wherenis
the total number of SFMs installed in the router. For example, in a system with
four SFMs,each SFM provides one-fourth of the forwarding capacity. Formore
information, see “Switching and Forwarding Module (SFM)” on page 19.
In the base configuration, the router hasone host module and multiple SFMs,
PCGs, power supplies,and cooling system components.
Safety Requirements, Warnings, and Guidelines
To avoidharm to yourself or the router as you install and maintainit, you need
to follow the guidelinesfor working with and near electrical equipment, as well
as the safety procedures forworking with Internet routers. For a discussion of
how to make the installationsite a safe environment, see “Preparing for Router
Installation” on page 59. For a list of safety warnings,see “Safety and Regulatory
Compliance Information” onpage 221 and particularly “Electrical Safety Guidelines
and Warnings” on page 227. However, providing an exhaustive set of guidelines
for working with electricalequipment is beyond the scope of this manual.
Safety Requirements, Warnings, and Guidelines 5