About Quality of Service for network traffic

Quality of Service (QoS) is a set of service requirements that the network must meet to ensure an adequate service level for data transmission. The goal of QoS is to provide a guaranteed delivery system for network traffic.

The QoS feature enables you to configure traffic queues for different priority network traffic, categorize and prioritize ingress traffic, and adjust priority settings for egress traffic. You can use these settings to ensure that important traffic is prioritized and handled first, before less important traffic. After categorizing and classifying the network traffic, you can assign priorities and schedule transmission.

QoS configuration is defined in the logical interconnect group and applied to the logical interconnect. QoS statistics are collected by the interconnects.

QoS configuration is only supported on VC Ethernet and VC FlexFabric interconnects on c7000 enclosures.

Classification for uplinks and downlinks

Uplink and downlink ports can be configured for ingress traffic classification based on the values of dot1p or DSCP or both in Ethernet and IP headers respectively.

Dot1p

A 3-bit field called the Priority Code Point (PCP) within an Ethernet frame header when using VLAN tagged frames as defined by IEEE 802.1Q. Eight different classes of service are available as expressed through the 3-bit PCP field.

DSCP

Differentiated Services Code Point (DSCP) is a field in an IP packet that enables different levels of service to be assigned to network traffic.

DSCP and Dot1p

For IP traffic use DSCP, and for non-IP traffic use dot1p priority.

For end-to-end QoS, all hops along the way must be configured with similar QoS policies of classification and traffic management. In an end-to-end QoS policy, traffic prioritization provides these benefits:
  • Greater bandwidth ensures higher priority for the associated traffic at the queue. At the interconnect, the packets are egressed based on the associated queue bandwidth.

  • Egress dot1p remarking helps achieve priority at the next hops in the network. If the queue egress traffic is remarked to a dot1p value, and that dot1p value is mapped to a queue in the next hops with higher bandwidth, the packets in the end-to-end network are treated with higher priority.

Active and Inactive QoS configurations with consistency state

While checking for consistency of a logical interconnect with its associated logical interconnect group, the compliance of inactive QoS configurations is also checked (inactive QoS configurations are not visible in the UI). Even if active QoS configurations are the same between a logical interconnect and an associated logical interconnect group, because of inconsistencies in inactive QoS configurations stored internally, a logical interconnect consistency status can appear as Inconsistent.

Perform an Update from group to bring the logical interconnect group and the logical interconnect into a consistent state.

The UI displays the currently active QoS configuration that you applied on the interconnects. In addition, two inactive QoS configurations are stored for Custom (with FCoE lossless) and Custom (without FCoE lossless) configuration types. These inactive configurations are the last known QoS configurations for the corresponding configuration types, applied previously on the associated logical interconnect, and the logical interconnect group.

QoS configuration types

The following QoS configuration types are available:

Passthrough

All ingress packets are not classified at egress. FCoE packets having a separate PG (Priority Group) are processed at ingress. There are no traffic classes, maps, or rules applied. Passthrough mode is equivalent to no QoS (QoS disabled).

Custom (with FCoE lossless)

Enables QoS and allows a customized configuration that includes FCoE class. The configuration defines two default system classes, Best Effort and FCoE lossless. You cannot edit the FCoE Lossless class and it is preconfigured for 50% bandwidth of the port. You can also configure up to six additional classes for non-FCoE Ethernet traffic.

Custom (without FCoE lossless)

Enables QoS and allows a customized configuration without FCoE. The configuration defines one system class, Best Effort. You can configure up to seven additional classes for non-FCoE Ethernet traffic.