Unspecified Bit Rate - Cisco 10000 Series Configuration Manual

QoS Inheritance
An ATM VC configured as CBR can transmit cells at peak cell rate (PCR) at any time and for any
duration. It can also transmit cells at a rate less than the PCR or even emit no cells. CBR is characterized
by PCR.

Unspecified Bit Rate

The unspecified bit rate (UBR) service class is intended for non-real-time applications that do not
require any maximum boundary on the transfer delay or on the cell loss ratio. The router delivers UBR
traffic only when there is spare bandwidth in the network. This behavior is enforced by setting the cell
loss priority (CLP) bit on UBR traffic when it enters a port.
The router delivers UBR traffic out to the network only when no other traffic is waiting to be served first.
The UBR traffic does not affect the trunk loading calculations performed by the switch software.
UBR is the default class of service running at the maximum line rate of the physical interface.
The router supports both unshaped (no PCR specified) and shaped UBRs.
Shaped UBR
Traffic shaping allows you to control the traffic going out an interface in order to match its flow to the
speed of the remote target interface and to ensure that the traffic conforms to policies contracted for it.
Traffic that adheres to a particular profile can be shaped to meet downstream requirements, thereby
eliminating bottlenecks in topologies with data-rate mismatches.
The Cisco 10000 series router supports traffic shaping for unspecified bit rate (UBR) traffic. Traffic
shaping is performed on a per-port basis and involves passing UBR traffic streams through VC queues
for scheduled rate shaping. When traffic shaping is enabled, all traffic exiting the port out to the network
is subject to VC scheduling based on the parameters you configure for the connection.
Cisco 10000 Series Router Quality of Service Configuration Guide
3-14
Chapter 3 Configuring QoS Policy Actions and Rules
OL-7433-09