Specifications

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2.2 The M20 Hardware System
The M20 Internet Backbone Router provides high-speed interfaces for large
networks and network applications, such as those supported by Internet
backbone service providers. Application-specific integrated circuits (ASICs), a
definitive part of the router design, enable the router to achieve data forwarding
rates that match current fiber-optic capacity.
The router accommodates up to four Flexible PIC Concentrators (FPCs), each of
which can be configured with a variety of network media types—all together
providing up to 64 physical interface ports per system. The router architecture
cleanly separates control operations from packet forwarding operations. This
design eliminates processing and traffic bottlenecks, permitting the router to
achieve full line-rate performance. Control operations in the router are performed
by the Routing Engine, which runs JUNOS Internet software to handle routing
protocols, traffic engineering, policy, policing, monitoring, and configuration
management. Forwarding operations in the router are performed by the Packet
Forwarding Engine, which consists of hardware, including ASICs, designed by
Juniper Networks. The router’s maximum aggregate throughput is 20 Gbps. The
router can forward traffic at line rate for any combination of Physical Interface
Cards (PICs) that does not exceed 3 Gbps on a single FPC. Any combination that
exceeds 3 Gbps is supported, but constitutes oversubscription.
The router is a modular, rack-mountable system. It is 14 in. (36 cm.) high, 19 in.
(48 cm.) wide, and 21 in. (54 cm.) deep. Its size allows up to five routers to be
installed in one standard, 78-inch-high Telco rack. A fully populated router weighs
approximately 134 lbs. (61 kg).
Component Replaceability
Most of the major router hardware components are field-replaceable. Field-
replaceable components fall into two categories:
§ Hot-removable and hot-insertable—You can remove and replace these
components without powering down the system and disrupting routing
functions. Power supplies, fan assemblies, and Flexible PIC
Concentrators (FPCs) are hot-removable and hot-insertable.
§ Hot-pluggable—You can remove and replace these components without
powering down the system, but the system either stops forwarding
packets or switches to a warm shutdown mode as long as the
component is removed. The System and Switch Board (SSB) and the
Routing Engine are hot-pluggable.
Component Redundancy
The router is designed so that no single point of failure can cause the entire
system to fail. The following major hardware modules are redundant:
§ Routing Engine and SSB—If there is a Routing Engine or SSB failure,
the redundant Routing Engine or SSB immediately assumes routing
functions.
§ Power supplies—The router has two power supplies, which share the
load evenly. If one of the power supplies fails, the second power supply
can supply full power to the router’s components.