As a reservation system, QoS enables you to allocate scarce network resources across multiple traffic types of varying importance. Using QoS, you can accurately control application traffic by bandwidth and sensitivity to delay. You configure QoS by defining networks and sites, applications and application groups, classification hierarchies, rules, and profiles.

The local appliance’s network and site configurations are used in QoS and path selection to properly shape and direct traffic on your network. Networks represent the WAN networks (MPLS, VSAT, internet) used for site-to-site communication. Sites represent collections of resources that share common WAN uplinks. The networks and sites you configure on the local appliance appear in its QoS and path selection Management Console pages.

Application definitions help you pinpoint, categorize, and assign a business priority to the traffic of specific or groups applications. Appliances include many predefined applications and application groups. You can add your own custom definitions, and customize the default ones.

QoS classes define minimum and maximum bandwidth allocation for shaping, queue protocol, differentiated services code point (DSCP) behavior, and priority for application traffic. Classes are assigned to applications through QoS rules and profiles. Classification occurs during connection setup for optimized traffic, before acceleration. QoS shaping and enforcement occurs after acceleration has begun.

QoS profiles are self-contained sets of classes and rules. Each profile represents a fully customizable class-shaping hierarchy where you can view the class layout and details at a glance. Apply profiles to sites to shape traffic to and from remote sites.

Sites provide the local appliance with the IP addresses of all existing subnets (including non-SteelHead sites). It’s important to define all remote subnets in the enterprise so they can be matched with the correct QoS profile. A default site is used as a catch-all for traffic that is not assigned to another site and for backhaul traffic.

By design, QoS is applied to both pass-through and optimized traffic; however, you can choose to classify either pass-through or optimized traffic. QoS is implemented in appliance’s operating system; it’s not a part of the optimization service. When the optimization service is disabled, all the traffic is pass-through and is still shaped by QoS. Flows can be incorrectly classified if there are asymmetric routes in the network when any of the QoS features are enabled.

It’s important to allocate the correct amount of bandwidth for each traffic class. The amount you specify reserves a predetermined amount of bandwidth for each traffic class. Bandwidth allocation is important for ensuring that a given class of traffic can’t consume more bandwidth than it is allowed. It’s also important to ensure that a given class of traffic has a minimum amount of bandwidth available for delivery of data through the network.

You configure QoS on client-side and server-side appliances to control the prioritization of different types of network traffic and to ensure that SteelHeads give certain network traffic; for example, Voice over IP (VoIP) has higher priority over other network traffic.