Quality of Service (QoS): Managing bandwidth effectively


A Quality of Service (QoS) network policy refers to the network-wide controls available to:

  • Ensure uniform and efficient traffic-handling throughout your network, while keeping the most important traffic moving at an acceptable speed, regardless of current bandwidth usage.

  • Exercise control over the priority settings of inbound traffic arriving in and travelling through your network.

Adding bandwidth can be a good idea, but is not always feasible and does not completely eliminate the potential for network congestion. There will always be points in the network where multiple traffic streams merge or where network links change speed and capacity. The impact and number of these congestion points will increase over time as more applications and devices are added to the network.

When network congestion occurs, it is important to move traffic on the basis of relative importance. However, without QoS prioritization, less important traffic consumes network bandwidth and slows down or halts the delivery of more important traffic. Without QoS, most traffic received by the switch is forwarded with the same priority it had upon entering the switch. In many cases, such traffic is normal priority and competes for bandwidth with all other normal-priority traffic, regardless of its relative importance to your organization's mission.

Using QoS to classify and prioritize network traffic

QoS is used to classify and prioritize traffic throughout a network. QoS enables you to establish an end-to-end traffic-priority policy to improve the control and throughput of important data. You can manage available bandwidth so that the most important traffic goes first. For example, you can use QoS to:

  • Upgrade or downgrade traffic from various servers.

  • Control the priority of traffic from dedicated VLANs or applications.

  • Change the priorities of traffic from various segments of your network as your business needs change.

  • Set priority policies in edge switches in your network to enable traffic-handling rules across the network.

    802.1p priority based on CoS (Class-of-Service) types and use of VLAN tags

    802.1p priority based on CoS (Class-of-Service) types and use of VLAN tags

    Application of Differentiated Services Codepoint (DSCP) policies

    Application of Differentiated Services Codepoint (DSCP) policies

Applying QoS to inbound traffic at the network edge

At the edge switch, QoS classifies certain traffic types and in some cases applies a DSCP policy. At the next hop (downstream switch) QoS honors the policies established at the edge switch. Further downstream, another switch may reclassify some traffic by applying new policies, and yet other downstream switches can be configured to honor the new policies.

Preserving QoS in outbound traffic in a VLAN

QoS is implemented in the form of rules or policies that are configured on the switch. Although you can use QoS to prioritize traffic only while it moves through the switch, you derive the maximum benefit by using QoS in an 802.1Q VLAN environment (with 802.1p priority tags) or in an untagged VLAN environment (with DSCP policies in which QoS sets priorities that downstream devices can support without re-classifying the traffic).

Using QoS to optimize existing network resources

By prioritizing traffic, QoS supports traffic growth on the network while optimizing the use of existing resources—and delaying the need for further investments in equipment and services. QoS enables you to:

  • Specify which traffic has higher or lower priority, regardless of current network bandwidth or the relative priority setting of the traffic when it is received on the switch.

  • Change (upgrade or downgrade) the priority of outbound traffic.

  • Override "illegal" packet priorities set by upstream devices or applications that use 802.1Q VLAN tagging with 802.1p priority tags.

Using classifier-based QoS to provide additional policy actions and aid migration in networks with legacy and OEM devices

HP Switch QoS configuration supports a classifier-based model that provides added functionality to create and manage QoS policies across a network consisting of HP switches, OEM and legacy devices.

The classifier-based configuration model is a single, simplified procedure and command syntax for cross-feature usage, which offers:

  • Finer granularity than globally-configured QoS for classifying IPv4 and IPv6 traffic

  • Additional actions for managing selected traffic, such as rate limiting and IP precedence marking

  • The application of QoS policies to inbound traffic flows on specific port and VLAN interfaces (instead of using only globally-configured, switch-wide QoS settings)

  • The use of configured traffic classes by different software features, such as QoS or port mirroring

Classifier-based QoS is designed to work with existing globally-configured, switch-wide QoS policies by allowing you to zoom in on a subset of port or VLAN traffic to further manage it. Classifier-based policies take precedence over and may override globally-configured, switch-wide QoS settings.

Classifier-based QoS policies provide greater control for managing network traffic. Using multiple match criteria, you can finely select and define the classes of traffic that you want to manage. QoS-specific actions determine how you can handle the selected traffic.