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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 42 Configuring PFC QoS
Understanding How PFCQoS Works
Understanding How PFC QoS Works
The term “PFC QoS” refers to QoS on the Cisco 7600 series router. PFC QoS is implemented on various
router components in addition to the PFC and any DFCs. These sections describe how PFC QoS works:
• Port Types Supported by PFC QoS, page 42-2
• Overview, page 42-2
• Component Overview, page 42-6
• Understanding Classification and Marking, page 42-16
• Understanding Port-Based Queue Types, page 42-22
Port Types Supported by PFC QoS
The PFC does not provide QoS for FlexWAN module ports. Refer to this publication for information
about FlexWAN module QoS features:
http://www.cisco.com/univercd/cc/td/doc/product/core/cis7600/cfgnotes/flexport/combo/index.htm
In all releases, PFC QoS supports LAN ports. LAN ports are Ethernet ports on Ethernet switching
modules, except for the 4-port Gigabit Ethernet WAN (GBIC) modules (OSM-4GE-WAN and
OSM-2+4GE-WAN+). Some OSMs have four Ethernet LAN ports in addition to WAN ports.
With Release 12.2(17b)SXA and later releases, PFC QoS supports optical services module (OSM) ports.
OSM ports are the WAN ports on OSMs. Refer to the following publication for information about
additional OSM QoS features:
http://www.cisco.com/univercd/cc/td/doc/product/core/cis7600/cfgnotes/osm_inst/index.htm
Overview
Typically, networks operate on a best-effort delivery basis, which means that all traffic has equal priority
and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an
equal chance of being dropped.
QoS makes network performance more predictable and bandwidth utilization more effective. QoS
selects (classifies) network traffic, uses or assigns QoS labels to indicate priority, makes the packets
comply with the configured resource usage limits (polices the traffic and marks the traffic), and provides
congestion avoidance where resource contention exists.
PFC QoS classification, policing, marking, and congestion avoidance is implemented in hardware on the
PFC, DFCs, and in LAN switching module port Application Specific Integrated Circuits (ASICs).
Note Cisco 7600 series routers do not support all of the MQC features (for example, Committed Access Rate
(CAR)) for traffic that is Layer 3 switched or Layer 2 switched in hardware. Because queuing is
implemented in the port ASICs, Cisco 7600 series routers do not support MQC-configured queuing.
Figure 42-1 shows an overview of QoS processing in a Cisco 7600 series router.