Congestion Avoidance; Differentiated Service Model For Cisco Ios Xr Software; Access Node Control Protocol - Cisco ASR 9000 Series Configuration Manual

Differentiated Service Model for Cisco IOS XR Software

Cisco IOS XR software includes traffic policing capabilities available on a per-class basis as well as class-based
shaping.
The traffic policing feature limits the input or output transmission rate of a class of traffic based on user-defined
criteria, and can mark packets by setting values such as IP Precedence, QoS group, or DSCP value.
Traffic shaping allows control over the traffic that leaves an interface to match its flow to the speed of the
remote target interface and ensure that the traffic conforms to the policies contracted for it. Thus, traffic
adhering to a particular profile can be shaped to meet downstream requirements, thereby eliminating bottlenecks
in topologies with data-rate mismatches.
Cisco IOS XR software supports a class-based traffic shaping method through a CLI mechanism in which
parameters are applied per class.
For detailed conceptual and configuration information about congestion management, see the "Configuring
Modular Quality of Service Congestion Management on Cisco ASR 9000 Series Routers" module.

Congestion Avoidance

Congestion avoidance techniques monitor network traffic flows in an effort to anticipate and avoid congestion
at common network and internetwork bottlenecks before problems occur. These techniques are designed to
provide preferential treatment for traffic (such as a video stream) that has been classified as real-time critical
under congestion situations while concurrently maximizing network throughput and capacity utilization and
minimizing packet loss and delay. Cisco IOS XR software supports the Random Early Detection (RED),
Weighted RED (WRED), and tail drop QoS congestion avoidance features.
For detailed conceptual and configuration information about congestion avoidance techniques, see the
"Configuring Modular Quality of Service Congestion Management on Cisco ASR 9000 Series Routers" module
in this guide.
Differentiated Service Model for Cisco IOS XR Software
Cisco IOS XR software supports a differentiated service that is a multiple-service model that can satisfy
different QoS requirements. However, unlike in 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 service based on the QoS specified
by each packet. This specification can occur in different ways, for example, 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 queuing.
The differentiated service model is used for several mission-critical applications and for providing end-to-end
QoS. Typically, this service model is appropriate for aggregate flows because it performs a relatively coarse
level of traffic classification.

Access Node Control Protocol

Access Node Control Protocol (ANCP) creates a control plane between a service-oriented aggregation device
and an access node (AN) (for example, a DSLAM) in order to perform QoS-related, service-related, and
subscriber-related operations. An ANCP Network Access Server (NAS) accepts and maintains ANCP
adjacencies (sessions with an ANCP neighbor), and sending and receiving ANCP messages.
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide, Release
6.1.x
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Modular QoS Overview