JUNOS Internet Software Network Operations Guide: Hardware
104 ! Understanding Key Router Components
6. The Queuing and Memory Interface ASIC sends the notification to the Switch
Interface ASIC facing the switch fabric, unless the destination is on the same
Packet Forwarding Engine. In this case, the notification is sent back to the
Switch Interface ASIC facing the outgoing ports, and the packets are sent to the
outgoing port without passing through the switch fabric (see Step 13).
7. The Switch Interface ASIC sends bandwidth requests through the switch fabric
to the destination port. The Switch Interface ASIC also issues read requests to
the Queuing and Memory Interface ASIC to begin reading data cells out of
memory.
8. The destination Switch Interface ASIC sends bandwidth grants through the
switch fabric to the originating Switch Interface ASIC.
9. Upon receipt of each bandwidth grant, the originating Switch Interface ASIC
sends a cell through the switch fabric to the destination Packet Forwarding
Engine.
10. The destination Switch Interface ASIC receives cells from the switch fabric. It
extracts the route lookup key from each cell, places it in a notification, and
forwards the notification to the T-series Internet Processor.
11. The T-series Internet Processor performs the route lookup, and forwards the
notification to the Queuing and Memory Interface ASIC.
12. The Queuing and Memory Interface ASIC forwards the notification, including
next-hop information, to the Switch Interface ASIC.
13. The Switch Interface ASIC sends read requests to the Queuing and Memory
Interface ASIC to read the data cells out of memory, and passes the cells to the
Layer 2/Layer 3 Packet Processing ASIC.
14. The Layer 2/Layer 3 Packet Processing ASIC reassembles the data cells into
packets, adds Layer 2 encapsulation, and sends the packets to the outgoing PIC
interface.
15. The outgoing PIC sends the packets out into the network.
Routing Engine
The Routing Engine consists of JUNOS software running on an Intel-based
Peripheral Component Interconnect (PCI) platform. The JUNOS kernel supports
JUNOS system processes which handle system management processes, routing
protocols, and control functions (see Figure 22 on page 105).
The Routing Engine handles all the routing protocol processes, as well as other
software processes that control the router interfaces, the chassis components,
system management, and user access to the router. These routing and software
processes run on top of a kernel that interacts with the Packet Forwarding Engine.
The Routing Engine has a dedicated 100-Mbps internal connection to the Packet
Forwarding Engine.
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