Bandwidth Calculations - Cisco 10000 Series Configuration Manual

Bandwidth Distribution Between Queues
Table 5-1
bandwidth.
Table 5-1
Command
bandwidth
priority

Bandwidth Calculations

The Cisco 10000 series router can commit up to 99 percent of the interface bandwidth to one or more
class queues. If you attempt to attach a policy map to an interface when the sum of the bandwidth
assigned to classes is greater than 99 percent of the available bandwidth, the router logs a warning
message and does not allocate the requested bandwidth to all of the classes. If the policy map is already
attached to other interfaces, it is removed from them.
For a physical interface, the total bandwidth is the bandwidth of the physical interface. The router
converts the minimum bandwidth that you specify to the nearest multiple of 1/255 (PRE1) or 1/65535
(PRE2) of the interface speed. When you request a value that is not a multiple of 1/255 or 1/65535, the
router chooses the nearest multiple.
The bandwidth percentage is based on the interface bandwidth. In a hierarchical policy, the bandwidth
percentage is based on the nearest parent shape rate.
By default, a minimum bandwidth guaranteed queue has buffers for up to 50 milliseconds of 256-byte
packets at line rate, but not less than 32 packets.
Cisco 10000 Series Router Quality of Service Configuration Guide
5-4
describes when a class configured with the bandwidth or priority command can use excess
Comparing When a Bandwidth and Priority Class Can Use Excess Bandwidth
Congestion
Allowed to exceed the allocated rate.
Not allowed to exceed the configured
rate.
If you configure a policer for the priority
class, the router polices the priority class
to the configured bps or percentage rate,
and discards any excess packets.
If you do not configure a policer, the
router guarantees a priority class 95
percent of the bandwidth, which can
result in bandwidth starvation of other
traffic classes.
Chapter 5 Distributing Bandwidth Between Queues
Non-Congestion
Allowed to exceed the
allocated rate.
Not allowed to exceed the
configured rate.
If you configure a policer, the
router polices the priority
class to the configured bps or
percentage rate, and discards
any excess packets.
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