22-2
ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter22 Configuring Quality of Service
About Layer 3 Switching Quality of Service

Best-Effort Service

Best effort is a single service model in which an application sends data whenever it must, in any quantity,
and without requesting permission or first informing the network. For best-effort service, the network
delivers data if it can, without any assurance of reliability, delay bounds, or throughput.
The Cisco IOS QoS feature that implements best-effort service is first-in, first-out (FIFO) queueing.
Best-effort service is suitable for a wide range of network applications such as general file transfers or
e-mail.

Integrated Service

Integrated service is a multiple service model that can accommodate multiple QoS requirements. In this
model the application requests a specific kind of service from the network before it sends data. Explicit
signalling makes the request. The application informs the network of its traffic profile and requests a
particular kind of service that can encompass its bandwidth and delay requirements. The application is
expected to send data only after it gets a confirmation from the network. It is also expected to send data
that lies within its described traffic profile.
The network performs admission control, based on information from the application and available
network resources. It also commits to meeting the QoS requirements of the application as long as the
traffic remains within the profile specifications. The network fulfills its commitment by maintaining
per-flow state and then performing packet classification, policing, and intelligent queueing based on that
state.

Differentiated Service

Differentiated service is a multiple service model that can satisfy differing QoS requirements. However,
unlike the integrated service model, an application using differentiated service does not explicitly signal
the router before sending data.
For differentiated service, the network tries to deliver a particular kind of se rvice based on the QoS
specified by each packet. This specification occurs in different ways, for example, while using the IP
Precedence bit settings in IP packets or source and destination addresses. The network uses the QoS
specification to classify, mark, shape, and police traffic, and to perform intelligent queueing.
About Layer 3 Switching Quality of Service
Layer 3 switching on the Catalyst 8500 switch router uses the packet classification feature in QoS to
partition network traffic into multiple priority levels of classes of service. For example, by using the
three precedence bits in the type-of-service (ToS) field of the IP packet header—two of the values are
reserved for other purposes—you can categorize packets into a limited set of up to six traffic classes.
After you classify packets, you can utilize other QOS features to assign the appropriate traffic handling
policies like congestion management and bandwidth allocation for each traffic class.