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Cisco 12000/10700 v3.1.1 Router Manager User Guide
OL-4455-01
Chapter 11 Layer 3 QoS
CAR and WR ED Overview

Towards the Fabric (ToFab)

ToFab describes the receive side traffic queues from a line card to (towards) the Switch fabric. Cisco
12000/10 720 Rout er M ana ger supp orts th is f unct iona lity thr ough the fol lowing dia logs,
•ToFab Configuration (used for creating ToFab policies)
•WRED Rx Configuration (used to apply/remove the ToFab policies for the chassis slots)
The ToFab Configur ation dialog lists all th e CosQ groups a lready created an d so the user can for m the
Slot-Tabl e-Cos (To Fab) by assoc iati ng t hem for any dest inati on sl ots. This basic ally defines a CosQ
group to any slot wit h refere nce to the sl ot (line c ard) for wh ich the pol icy would be applied.
Note On ly one C osQ grou p c an b e ap plied to a dest ina tio n slo t.
The WRED Rx Configuration dialog is used to apply the same against a Preferred line card (Slot).
Similar to CosQ gro up manage ment, Engine Type Suppor t is also provided.
Any ToFab policy that is cr eated is available unde r the Cont ainer View Layer3Q oSView ==>
WRED-MDRR ==> TOFABPolicies.
The servi ce me nu fo r ToFab manage m ent is available fro m the mo dule an d i ts p ar en ts. T he ToFab
dialogs ca n also be laun ched fo r the Laye r3QoSView conta iner.

MDRR Overview

Modified Deficit Round Robin (MDRR) is a traffic latency control f unction. It allows the operators to
guarante e tra ffic l ate ncy for di fferent iate d f lows by contr olli ng t h e pa cket de -qu euin g pro cess. Packet
classification is based on IP Precedence. MDRR differs from DRR in that one of the eight available
queues is designa ted as a low-latency que ue.
There are t wo basic modes of operation which govern how packet s are de-queued from the low-latency
queue in r ela tio n to ot her qu eu es. They a re:
•Alternate Priority—Queues are serviced by alternating between the low-latency queue & the other
queues in roun d-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 1 2000/ 10720 Rou ter Man ager pr ovides MDRR sup port via C OS Qu eue Grou ps: t he ope rat or
creates a COS Queue Group & uses the MDRR configur ation Window to encapsulate the required
parameters. The COS Queue Group is th en available to be applied to any interface.