Cisco 12000/10700 V3.1.1 - Manual (Page 290)

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Cisco 12000/10700 v3.1.1 Router Manager User Guide
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Chapter 11 Layer 3 QoS
CAR and WRED Overview
Towards the Fabric (ToFab)
ToFab describes the receive side traffic queues from a line card to (towards) the Switch fabric. Cisco
12000/10720 Router Manager supports this functionality through the following dialogs,
• ToFab Configuration (used for creating ToFab policies)
• WRED Rx Configuration (used to apply/remove the ToFab policies for the chassis slots)
The ToFab Configuration dialog lists all the CosQ groups already created and so the user can form the
Slot-Table-Cos (ToFab) by associating them for any destination slots. This basically defines a CosQ
group to any slot with reference to the slot (line card) for which the policy would be applied.
Note Only one CosQ group can be applied to a destination slot.
The WRED Rx Configuration dialog is used to apply the same against a Preferred line card (Slot).
Similar to CosQ group management, Engine Type Support is also provided.
Any ToFab policy that is created is available under the Container View Layer3QoSView ==>
WRED-MDRR ==> TOFABPolicies.
The service menu for ToFab management is available from the module and its parents. The ToFab
dialogs can also be launched for the Layer3QoSView container.
MDRR Overview
Modified Deficit Round Robin (MDRR) is a traffic latency control function. It allows the operators to
guarantee traffic latency for differentiated flows by controlling the packet de-queuing process. Packet
classification is based on IP Precedence. MDRR differs from DRR in that one of the eight available
queues is designated as a low-latency queue.
There are two basic modes of operation which govern how packets are de-queued from the low-latency
queue in relation to other queues. They are:
• Alternate Priority—Queues are serviced by alternating between the low-latency queue & the other
queues in round-robin.
• Strict Priority—Low-latency queue is continually serviced to keep it empty.
MDRR in Cisco 12000/10720 Router Manager
The MDRR implementation uses COS Queue Groups to encapsulate the required profile. Consequently,
Cisco 12000/10720 Router Manager provides MDRR support via COS Queue Groups: the operator
creates a COS Queue Group & uses the MDRR configuration Window to encapsulate the required
parameters. The COS Queue Group is then available to be applied to any interface.