Hardware Component Overview
Packet Forwarding Engine
11
A regular PIC is hot-removable and hot-insertable in the sense that its absence does not
disrupt routing functions; however, you must completely remove its host FPC from the
chassis before removing the PIC, which affects all PICs on the FPC. For replacement
instructions, see “Replace a PIC” on page 167.
Quad-wide PICs, such as the 4-port Gigabit Ethernet and OC-48/STM-16 SONET/SDH PICs,
occupy an entire FPC slot and are hot-removable and hot-insertable, as described in
“Field-Replaceable Units (FRUs)” on page 4. The instructions for replacing a quad-wide PIC
are the same as for an FPC. See “Replace an FPC or Quad-wide PIC” on page 163.
PIC Components
Most PICs supported on the M40 router have the following components, but for complete
specifications see the
M20 and M40 Internet R outers PIC Guide
. For information about
pinouts for PIC cable connectors, see “Cable Connectors and Pinouts” on page 207.
One or more cable connector ports—Accept a network media connector.
LEDs—Indicate PIC and port status. Most PICs have an LED labeled
STATUS
on the PIC
faceplate. Some PICs have additional LEDs, often one per port. The meaning of the LED
states differs for various PICs. For more information, see the
M20 and M40 Internet
Routers PIC Guide
.
Flexible PIC Concentrators (FPCs)
Flexible PIC Concentrators (FPCs) house the PICs that connect the router to network media
(for information about PICs, see “Physical Interface Cards (PICs)” on page 10). Up to eight
FPCs install vertically into the backplane from the front of the chassis. The FPC slots are
numbered left to right, from
0
(zero) through
7
. Each FPC accommodates up to four PICs and
the PIC slots in each FPC are numbered from
0
(zero) through
3
, top to bottom.
An FPC can be installed into any FPC slot, regardless of the PICs it contains, and any
combination of slots can be used. If a slot is empty, you must install a blank FPC panel to
shield it, so that cooling air can circulate properly throughout the card cage. Figure 4, which
shows a chassis with an FPC in slot
7
, omits the blank FPC panels to show the FPC’s position
in the card cage.
The main function of an FPC is to connect the PICs installed in it to the other router
components. The I/O Manager ASIC on the FPC divides each incoming data packet into
64-byte cells, which the Distributed Buffer Manager ASIC on the backplane distributes among
the memory buffers located on and shared by all installed FPCs. After the SCB decides how to
forward a packet, the I/O Manager ASIC on the FPC reassembles the corresponding data cells
back into network-packet form and passes the packet to the appropriate PIC for transmission
to the network. For more information, see “Data Flow through the Packet Forwarding
Engine” on page 33.
FPCs are hot-removable and hot-insertable, as described in “Field-Replaceable Units (FRUs)”
on page 4. When you remove or install an FPC, packet forwarding halts for about 200 ms
while the Packet Forwarding Engine adjusts to the change in the amount of memory
available in the pool located on and shared by all FPCs. When you install an FPC into a
functioning router, press its offline button to activate it and the PICs installed in it. The
Routing Engine downloads the FPC software, the FPC runs its diagnostics, and the PICs
housed on the FPC are enabled. Forwarding continues uninterrupted during this process. For
FPC replacement instructions, see “Replace an FPC or Quad-wide PIC” on page 163.
