Enhancing WiFi Connections in Excessive-Density Environments

In a current article, I mentioned the shortcomings of improvised client-steering methods used for band steering, load balancing, and sticky shopper prevention in WiFi networks, and the way the Wi-Fi Alliance is working to deal with them. Final month, the alliance launched a certification referred to as Wi-Fi Licensed Agile Multiband. It ratifies an clever client-steering protocol based mostly on IEEE 802.11okay and 802.11v requirements.

Concurrently, the Wi-Fi Alliance has introduced one other certification referred to as Wi-Fi Licensed Optimized Connectivity, which is designed to optimize shopper connection setup in excessive density environments and relies on the IEEE 802.11ai customary that was ratified earlier this yr. The certification introduces two most important enhancements: probing flood discount throughout AP discovery carried out by WiFi purchasers and quick preliminary hyperlink setup to the chosen AP after discovery.

Probing flood

There are conditions when plenty of customers concurrently enter a WiFi protection space. For instance, when a flight or a practice arrives, numerous folks enter the WiFi protection space on the airport or the practice station gate on the similar time, and their WiFi units begin scanning for APs. Purchasers scan for APs by sending probe request frames and APs reply with probe response frames. Purchasers ship probe requests for networks (SSIDs) configured in WiFi profile. If an AP helps the particular SSID, it responds to the shopper with the probe response.

Purchasers additionally ship “wildcard” probe requests to which a number of APs reply with probe responses. The person probe frames include small quantities of information, however as a result of they’re transmitted at a low date charge, they devour lengthy air time. The web impact is that the shared wi-fi medium will get crammed with probe request/response transmissions. This adversely impacts WiFi throughput of already related purchasers.

Optimized Connectivity offers a number of enhancements to scale back probing visitors. Within the conventional IEEE 802.11 protocol, a probe response from the AP is distributed to the unicast deal with of the shopper that requested it. In Optimized Connectivity, the probe response is distributed to the published deal with so that every one purchasers can obtain it and uncover that AP. Up to now, the standard interval at which an AP sends periodic beacons promoting itself is 100 milliseconds. This interval is simply too lengthy for purchasers as they should scan a number of channels in brief time. So, purchasers probe with out ready for beacons.

Optimized Connectivity reduces the AP promoting interval from 100 ms to simply 20 ms to facilitate faster discovery with out probing. To keep away from frequent commercials consuming giant airtime, a shorter beacon format referred to as FILS Discovery is launched for commercials between regular 100 ms beacons. On this expertise, the AP additionally has the choice to incorporate details about neighboring APs (referred to as Lowered Neighbor Report) in beacons, quick preliminary hyperlink setup discovery and probe responses. This facilitates faster discovery of neighboring APs for purchasers.

Optimized Connectivity additionally requires purchasers to attend for 20 ms upon visiting a channel earlier than beginning to probe. An exception to this rule is allowed when the shopper is aware of some SSIDs to be hidden, i.e., not marketed in beacons and FILS Discovery frames.

There are further inefficiencies in conventional probing that this expertise addresses. For instance, if a shopper doesn’t obtain a probe response from an AP earlier than it switches channels to find different APs, the late probe response leads to wasteful wi-fi transmission. So as to add to the issue, for the reason that AP doesn’t obtain MAC layer ACK from the shopper for that probe response, it retransmits it, inflicting one other wasted transmission. To keep away from losing wi-fi capability, the shopper can now talk within the probe request to the AP how lengthy it’ll keep on that channel.

All these options in Optimized Connectivity are designed to facilitate AP and shopper to restrict probing visitors in the course of the AP discovery part. After the invention part, shopper selects an AP to connect with and initiates connection setup to the chosen AP. This system additionally introduces enhancements to hurry up this connection setup as follows.

Quick preliminary hyperlink setup

In at this time’s WiFi networks, on the entry level of the WiFi protection, a shopper should carry out a full connection institution process with the AP to entry the community. This motion consists of plenty of steps equivalent to L2 authentication and affiliation, EAP authentication, EAPOL, and DHCP. This exercise generates many frames in each instructions over the wi-fi hyperlink. Optimized Connectivity introduces Quick Preliminary Hyperlink Setup (FILS) enchancment based mostly on the IETF’s EAP re-authentication protocol (ERP). With FILS, the preliminary connection setup may be accomplished in simply 4 frames transmitted on the wi-fi hyperlink.

ERP permits quick authentication by remembering on the shopper and the backend AAA server the previous authentication state established at an earlier cut-off date. Remembering this state permits for fast shopper admission thereby eliminating the whole EAP authentication from the present connection setup. Notably, EAP authentication is normally the largest contributor to connection setup latency. Additional, FILS introduces piggybacking of ERP and EAPOL messages on L2 authentication and affiliation messages. It performs DHCP deal with acquisition in parallel with the L2 authentication and affiliation steps.

As soon as the preliminary connection is established, subsequent roaming between APs is achieved utilizing methods which are already fashionable and accessible in at this time’s WiFi networks equivalent to 802.11r Quick Transition.

Whereas I used an airport and practice station instance in the beginning to explain the motivation behind Optimized Connectivity — referred to as the “Tokyo station” state of affairs within the requirements group – this system can also be helpful in different crowded environments equivalent to stadiums, malls, and film theaters.

Countering LAA-LTE

The Wi-Fi Alliance’s curiosity in enhancing public WiFi efficiency is partially motivated by the will to face as much as License Assisted Entry LTE expertise. LAA-LTE permits operators and repair suppliers to function LTE wi-fi entry networks within the 5 GHz unlicensed spectrum. One of many advantages cited for LAA-LTE is its environment friendly air interface that performs higher in high-density networks in comparison with conventional WiFi. Nonetheless, LAA-LTE requires a leg within the licensed spectrum to help its management channel; WiFi doesn’t require any licensed spectrum in any respect.

By introducing options that make WiFi air interfaces extra environment friendly, WiFi can stay a viable expertise for public wi-fi entry. Count on to see extra such enhancements sooner or later, significantly to align with mainstream adoption of 802.11ax.


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