QoS (Quality of Service) involves prioritization of network traffic. QoS is the idea that transmission rates, error rates, and other characteristics can be measured, improved, and, to some extent, guaranteed in advance. QoS can be targeted at a network interface, toward a given server or router’s performance, or in terms of specific applications. A network monitoring system must typically be deployed as part of QoS, to insure that networks are performing at the desired level.
QoS is especially important for the new generation of Internet applications such as VoIP, video-on-demand and other consumer services.
Most of the more modern QoS tools from Cisco use configuration commands that conform to a convention called the Modular QoS CLI (MQC), which significantly reduces the complexity of QoS configuration as compared to QoS tools that don’t use MQC commands.
Cisco Modular QOS is a new approach for classification of the various QoS mechanisms in fact it helped resolve these problems by defining a common set of configuration commands to configure most QoS features in a router or switch. MQC defines a new set of configuration commands that are typed in using the same IOS CLI, in configuration mode.
Cisco MQC was first introduced as a framework for Class-Based Weighed Fair Queuing (CBWFQ) in Cisco IOS Software Release 12.0(5)T. It has evolved to support the majority of the QoS features. Using MQC requires a three-step process:
- Define a class-map. The first step in QoS deployment is to identify the interesting traffic (ie: classify the packets). This step defines a grouping of network traffic-a class-map in MQC terminology-with various classification tools: Access Control Lists (ACLs), IP addresses, IP precedence, IP Differentiated Services Code Point (DSCP), IEEE 802.1p, MPLS EXP, and Cisco Network Based Application Recognition (NBAR).
- Define a policy-map. Decide what to do with a group once its traffic has been identified. This step can be considered the actual construction of a QoS policy-a policy-map in MQC terminology-by choosing the group of traffic (ie: class-map) on which to perform QoS functions. Examples of QoS functions are queuing, dropping, policing, shaping, and marking.
- Apply the policy-map. Apply the appropriate policy-map to the desired interfaces, sub-interfaces, or Asynchronous Transfer Mode (ATM) or Frame Relay Permanent Virtual Circuits (PVCs).