Nortel Networks 8005DC - Manual (Page 23)

M mode configuration requirements 23
The RSP2 determines the information the fabric needs to carry the packet
to the correct egress point and determines the physical egress port. As part
of the lookup process, the RSP2 may also determine and record the egress
queue ID and pass it to the egress RSP2.
Encapsulation is the most significant operation that the egress RSP2
performs. To specify the egress queue, the queuing and traffic shaping
functions use:
• encapsulation information from the egress RSP2
• MAC and IP packet headers
• Quality of Service (QoS) bits
The F2E egress ASIC supports the FFE QoS, including the functions
of random early drop, queuing and selection, traffic shaping, and
communicating to other similar R modules. Similarly, the F2I ingress ASIC
provides packet policing and marking.
Each DPM also consists of the following:
• One Fast TAPmux (FTAP) interface to the Metro Ethernet Routing
Switch 8600 Switch Fabric Modules
• One Feedback Output Queue Manager (FOQ) Field-Programmable
Gate Array (FPGA)
The FTAP ASIC connects each DPM to the CPU/Switch Fabric modules
through the Metro Ethernet Routing Switch 8600 switching backplane.
The FOQ Management system collects information about the state of
queues, packet storage elements, and the fabric. This information is
available to the F2I at the point at which packets are segmented for entry
to the fabric. When congestion exists, Metro Ethernet Routing Switch
8600 modules with a BFM (pre-E, E, and M modules) use fabric feedback
information only at this point to drop packets.
The FOQ mechanism also provides information about the state of each
of the egress queues and on the fullness of the F2E reassembly function
buffers and queues. The F2E reports this information to the FOQ Manager
FPGA on each module. The constellation of these FOQ FPGAs (one per
DPM) drives a shared backplane bus that each FPGA senses. Therefore,
each R module has pertinent information about the state of all other R
modules in the system.
M mode configuration requirements
M mode supports the Metro Ethernet Routing Switch 8600 M module feature
set. Full support of M mode requires the following configuration conditions:
• The chassis must include at least one 8691omSF CPU module.
Nortel Metro Ethernet Routing Switch 8600
Installation — Modules
NN46220-306 02.02 Standard
4.2 7 July 2008
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