Juniper T640 Hardware Manual page 41

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The Queuing and Memory Interface ASICs pass the data cells to memory for buffering.
4.
The T-series Internet Processor performs the route lookup and forwards the notification
5.
to the Queuing and Memory Interface ASIC.
The Queuing and Memory Interface ASIC sends the notification to the Switch Interface
6.
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).
The Switch Interface ASIC sends bandwidth requests through the switch fabric to the
7.
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.
The destination Switch Interface ASIC sends bandwidth grants through the switch
8.
fabric to the originating Switch Interface ASIC.
On receipt of each bandwidth grant, the originating Switch Interface ASIC sends a
9.
cell through the switch fabric to the destination Packet Forwarding Engine.
The destination Switch Interface ASIC receives cells from the switch fabric. It extracts
10.
the route lookup key from each cell, places it in a notification, and forwards the
notification to the T-series Internet Processor.
The T-series Internet Processor performs the route lookup, and forwards the
11.
notification to the Queuing and Memory Interface ASIC.
The Queuing and Memory Interface ASIC forwards the notification, including next-hop
12.
information, to the Switch Interface ASIC.
The Switch Interface ASIC sends read requests to the Queuing and Memory Interface
13.
ASIC to read the data cells out of memory, and passes the cells to the Layer 2/Layer
3 Packet Processing ASIC.
The Layer 2/Layer 3 Packet Processing ASIC reassembles the data cells into packets,
14.
adds Layer 2 encapsulation, and sends the packets to the outgoing PIC interface.
The outgoing PIC sends the packets out into the network.
15.
T640 Chassis Description on page 13
T640 Physical Specifications on page 421
Replacing T640 Packet Forwarding Engine Components on page 287
Chapter 2: T640 Router System Architecture Overview
9