Type of QoS Scheduling

Jul 08,2008 00:00 by admin

Type of QoS Scheduling

Switch1 (enable) show port capabilities 10/3

Model                    WS-X6248-RJ-45

Port                     3/1

Type                     10/100BaseTX

Speed                    auto,10,100

Duplex                   half,full

Trunk encap type         802.1Q,ISL

Trunk mode               on,off,desirable,auto,nonegotiate

Channel                  yes

Broadcast suppression    percentage(0-100)

Flow control             receive-(off,on),send-(off)

Security                 yes

Dot1x                    yes

Membership               static,dynamic

Fast start               yes

QOS scheduling           rx-(1q4t),tx-(2q2t)

CoS rewrite              yes

ToS rewrite              DSCP

UDLD                     yes

Inline power             no

AuxiliaryVlan            1..1000,1025..4094,untagged,dot1p,none

SPAN                     source,destination

COPS port group          3/1-48

Link debounce timer      yes

Dot1q-all-tagged         yes

Since 1q4t has only 1 queue, all incoming frames will be placed in this single queue. However, if the queue starts to become congested, frames will be dropped based on their CoS values. The following lists the defaults for each CoS value:

CoS 0 and 1 are mapped to threshold 1 (set at 50 percent)
CoS 2 and 3 are mapped to threshold 2 (set at 60 percent)
CoS 4 and 5 are mapped to threshold 3 (set at 80 percent)
CoS 6 and 7 are mapped to threshold 4 (set at 100 percent)

Any incoming packet with CoS setting of 0 or 1 that is mapped to threshold 1 will be dropped if the port buffer is at 50 percent or higher. The show qos info command in Example 8-5 shows the default mapping for CoS and its associated drop threshold level on a Catalyst switch.