Specifications

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SSB Hotplug
If the user inserts an SSB while the other SSB is the master, then the switchover
will not occur whether or not the redundancy setting has been configured. The
switch-over event will only occur if there is a switch-over condition as described
above. A syslog entry is generated for each hotplug event so that the provider
has a record of what was added or removed and when.
4.2.4 Redundant power supplies
The Mxxx have redundant power supplies. There are two fully redundant load-
sharing power supplies. A single power supply can provide full power (up to 1500
watts) for as long as the system is operational. Redundancy is necessary only in
case of power supply failure. When both power supplies are functioning they
perform load sharing and each one runs at 50% load. When one fails, the other
one automatically takes 100% of the load.
4.2.5 Redundant chassis fans
The Mxxx have redundant fans. The M40 has upper and lower cooling trays,
which cool a fully loaded system of any card complement. The M40 can survive
the failure of either the upper or lower cooling tray, or an individual fan impeller
in each tray without any system degradation under the published operation
specifications.
4.2.6 Hot swap and modularity
All the components below are field replaceable and hot swappable.
§ Power supplies
§ Routing engine
§ System control board and System and Switch Board
§ Flexible PIC concentrators
§ Impellers
§ Top tray
§ Bottom tray (includes craft interface)
§ Rear fans and fan assembly
§ Front air filter
The PICs are modular components that plug into the FPC. With the exception of
OC48 and OC192, which takes up the whole FPC, all other PICs can be mixed
and matched within a FPC.
No intervention is required to bring the FPCs or PICs physically online when
installed into a running system.
FPCs are hot-insertable and hot-removable. Each FPC is mounted on a card
carrier. When you remove an FPC and install a new one, the backplane flushes
the entire system memory pool before the new card is brought online--a process
that takes about 200 milliseconds.
When you install an FPC into a running system, the Routing Engine downloads
the FPC software, the FPC runs its diagnostics, and the PICs on the FPC slot are
enabled. No interruption occurs to the routing functions.
PICs must be installed or removed while the FPC is removed from the chassis.
PICs are plugged into the FPC connectors as well as screwed onto the FPC
board.
The Mxxx have been designed to be modular both from hardware and software
standpoint.
4.3 Logical Redundancy
4.3.1 Software Redundancy
JUNOS software also features a modular design, with separate programs running
in protected memory space on top of an independent operating system. Unlike
monolithic, unprotected operating system designs, which are prone to system-
wide failure, the protected, modular approach improves reliability by ensuring that
modifications made to one module have no unwanted side-effects on other