BSS Priority
Feature Overview
The Airtime Fairness (ATF) functionality ensures that all VAPs and their clients on a radio receive equal airtime. VAPs refer to the capability of a single physical access point (AP) to support multiple, distinct wireless networks by broadcasting multiple Service Set Identifiers (SSIDs). BSS Priority allows the configuration of lower priority for specific VAPs, thus reducing their clients' airtime compared to those connected to higher-priority VAPs. The ATF feature calculates the total number of clients per radio and shares airtime equally. However, with BSS Priority, clients on lower priority VAPs receive further reduced airtime units, ensuring higher priority VAPs and their clients get more airtime.
Functional Requirements
- Integration with ATF: BSS Priority works hand-in-hand with ATF to manage and allocate airtime fairly across different VAPs on the same radio.
- Periodic and Event-Driven Evaluation: Airtime units are recalculated every second and whenever a client joins or leaves a VAP, ensuring dynamic and responsive airtime management.
- Storage in Peer Structure: The allocated airtime for each client is stored in their respective peer structures, facilitating efficient tracking and management of airtime distribution.
Platform Requirements
Implementing BSS Priority requires compatible hardware (APs and controllers), support for IEEE Std. 802.11ac and QoS, integration with the ATF functionality, and effective configuration and monitoring tools. Ensuring these platform requirements are met will enable efficient and effective use of BSS Priority to optimize airtime allocation and network performance.
Limitations of Current ATF Implementation
- Lapsing of Unused Airtime Units for High Priority VAP Clients: Unused airtime units for clients connected to high-priority VAPs are not carried over or reallocated. This could lead to inefficiencies, as valuable airtime is wasted if not used by high-priority clients.
- Reallocation of Unused Airtime Units for Low Priority VAP Clients: Unused airtime units for clients connected to low-priority VAPs can be utilized by high-priority VAP clients. While this helps in utilizing available airtime, it can lead to a scenario where low-priority clients might consistently receive less airtime if high-priority clients always consume the extra available airtime.
- Applicability Only to Downlink (DL) Traffic: This implementation only applies to downlink traffic (from AP to clients). Uplink traffic (from clients to AP) is not affected by these airtime allocation rules, which may result in inconsistent performance improvements.
- Client Count-Based Allocation: Airtime allocation is based purely on the number of connected clients. This approach does not account for the actual data requirements or usage patterns of the clients, which can lead to suboptimal allocation in real-world usage scenarios where client demands vary significantly.
- Lack of Fairness for Low Priority Clients: Low-priority VAP clients may consistently receive less airtime, especially in environments with heavy traffic from high-priority VAP clients. This could result in poor performance for clients connected to low-priority VAPs.
Best Practices
BSS Priority complements the IEEE 802.11ac standard by allowing finely tuned control over airtime allocation among VAPs on the same radio. This ensures that the advanced capabilities of IEEE 802.11ac are used efficiently to provide the best possible performance for different types of users and applications in a Wi-Fi network.
Prerequisites
BSS Priority in a Wi-Fi network has several prerequisites to ensure proper functionality and integration. The key prerequisites are listed below: