The tremendous growth of real-time communications applications over Wi-Fi®, such as videoconferencing and interactive gaming, has prompted an evolution in traditional Quality of Service (QoS) techniques. Wi-Fi CERTIFIED QoS Management™ addresses the evolving needs of users, enabling consistent QoS treatment in Wi-Fi networks.
The need for QoS
Some applications can tolerate a degree of traffic delays, jitter, and traffic loss – others cannot. An enterprise user expects to run a videoconference without garbled voices or pixelated PowerPoint slides. Similarly, a mobile gaming user expects to enjoy smooth gameplay without lag time or jitter. To meet the service expectations for such inelastic applications in dynamic Wi-Fi environments, in addition to high throughput and mobility, consistency of QoS treatment policies is important.
The foundation of Wi-Fi QoS: Wi-Fi Multimedia™ (WMM®)
Wi-Fi Alliance® introduced the Wi-Fi Multimedia (WMM) program in 2004, as an initial step to standardize Wi-Fi QoS technologies. WMM adopted quality of service enhancements defined in the IEEE 802.11e standard. These enhancements included four access categories: Voice, Video, Best Effort, and Background, which are mapped into four separate queues. The traffic flows are classified into these access categories according to their User Priority and each access category contends for the radio frequency (RF) medium using the same rules but employs different channel access parameters. These parameters guarantee performance differentiation among the categories.
For consistent QoS, the application, client device, and Wi-Fi network need to recognize and use the standardized QoS foundations of WMM in their configurations. But it is also important to align QoS treatments between wired and wireless networks; however, there are inconsistencies in deployment. The industry needs to adopt a standardized way to map Differentiated Service Code Point (DSCP) values to WMM User Priorities to have consistent QoS treatments between wired IP and wireless Wi-Fi networks.
Wi-Fi QoS Management™ enhances traditional QoS
Wi-Fi QoS Management builds upon and extends WMM with new technologies that align treatments between wired and Wi-Fi networks and enable clients and APs to negotiate and request identified IP flows be assigned to specific access categories defined by WMM. To achieve these goals, the program incorporates two key technologies:
- Differentiated Service Code Point (DSCP) mapping: aligns QoS treatment across Wi-Fi and wired networks and also enables network managers to configure specific QoS policies
- Mirrored Stream Classification Service (MSCS): enables a client device to request the AP to apply specific QoS treatment of downlink IP data flows using QoS mirroring
Differentiated Service Code Point (DSCP) mapping
To address inconsistencies across the industry in how DSCP is mapped to WMM User Priorities and access categories, Wi-Fi QoS Management adopted IETF RFC 8325 as the default mapping to reconcile the marking recommendations offered by the IETF and the IEEE. This recommendation has been widely recognized and accepted by the industry.
Wi-Fi QoS Management also provides a QoS Map feature (as defined in IEEE 802.11u), which enables administrators to configure non-default mapping tables on client devices and APs when necessary. The QoS Map feature can be used to change the prioritization of flows which are mapped in certain ways and allows the mapping of non-standard DSCP values to be specified—all under control of the network administrator. These administrators can configure the tables that get pushed out to client devices using 802.11 signaling.
Mirrored Stream Classification Service (MSCS)
There are also use cases in residential and guest networks where the ingress flows (downlink) coming from the public internet do not have DSCP markings or are not mapped at all. To address this, Wi-Fi QoS Management provides a way for the client and application to get the AP to map flows to the appropriate QoS treatment. Rather than requiring the client to decipher complex IT templates to make the request, Wi-Fi QoS Management introduced a mirroring mechanism defined in IEEE 802.11 rev md, known as MSCS.
MSCS causes the AP to prioritize traffic in the downlink the same way that the client device prioritizes traffic in the uplink. This bidirectional QoS treatment ensures consistent, controlled, round trip latency, and delivers a positive connectivity experience, even when the Wi-Fi channel is congested with other competing network traffic.
Wi-Fi QoS Management benefits
Wi-Fi QoS Management results in improved performance for latency-sensitive network traffic and an enhanced quality of experience for end users. The program enables consistent QoS treatments to provide better experiences in real-time applications, with reduced latency and jitter in inelastic applications such as online gaming, fewer outages in immersive applications, and reduced lag time in access to interactive cloud and edge services.
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