T640 Component Redundancy

• Switch Interface Boards (SIBs)—The router has five SIBs. A T640 router that is connected to a TX Matrix platform requires T640-SIBs ; see T640 Switch Interface Boards (SIBs) Description) Each Type 1 FPC and Type 2 FPC has a dedicated ASIC with five high-speed links that connect to the SIBs (one link per SIB). Each Type 3 FPC has two dedicated ASICs, and each ASIC has five high-speed links that connect to the SIBs (a total of 10 links). Each Type 4 FPC has one dedicated ASIC with ten high-speed links that connect to the SIBs (two links per SIB). One of the five SIBs—usually SIB4—acts as a backup to the remaining four SIBs. If a SIB fails, the backup SIB becomes active and traffic forwarding continues without any degradation. When the failed SIB is replaced, it becomes the new backup.
• Host subsystem—The host subsystem consists of a Routing Engine functioning together with a control board. The router can have one or two host subsystems. If two host subsystems are installed, one functions as the master and the other functions as the backup. If the master host subsystem (or either of its components) fails, the backup can take over as the master. To operate, each host subsystem requires a Routing Engine installed in an adjacent slot to a control board.

  If the Routing Engines are configured for graceful switchover, the backup Routing Engine automatically synchronizes its configuration and state with the master Routing Engine. Any update to the master Routing Engine state is replicated on the backup Routing Engine. If the backup Routing Engine assumes mastership, packet forwarding continues through the router without interruption. For more information about graceful switchover, see the Junos OS System Basics Configuration Guide .

• SONET Clock Generators (SCGs)—The router has a standard configuration of one SCG. A second can be purchased to function as backup. If one SCG fails, the other becomes the master SCG. Mastership of the SCGs is independent of the host subsystem, so routing functions are not affected.
• Power supplies—The router has two power supplies, which share the load evenly. If one power supply fails, the other power supply can provide full power to the router indefinitely.
• Cooling system—The cooling system has redundant components, which are controlled by the host subsystem. If one of the fans fails, the host subsystem increases the speed of the remaining fans to provide sufficient cooling for the router indefinitely.