Aerohive Adds SLA Monitoring and Enforcement

By Lisa Phifer

September 01, 2009

HiveOS 3.4 Performance Sentinel and Airtime Boost to help admins track and ensure WLAN compliance based on per-user throughput targets.

Norman Elton, network engineer at the College of William & Mary, is really looking forward to Performance Sentinel, a continuous service level compliance monitoring feature included in Aerohive's upcoming HiveOS 3.4.

"When we have thousands of students show up in one weekend, we don't really have any way of knowing whether they're all getting good wireless service," he said. "Do we have 10 percent with throughput problems or do we have 60 percent? When someone calls for help, is the issue likely to be AP bandwidth, an antiquated laptop, or just an overloaded Website?"

Admins like Elton not only welcome the readily-available, easily-grasped insight promised by Performance Sentinel—they can also respond pro-actively using Airtime Boost, an option that gives non-compliant stations a little extra air time as needed to achieve defined targets. Both upgrades will be included in release 3.4 of Aerohive HiveOS and HiveManager.

Getting a grip on goodput

The campus network managed by Elton includes over 1000 legacy Cisco/Airespace APs, plus 100 Aerohive HiveAPs in a just-launched school-of-business WLAN. "We're like a corporate network in that we support faculty and staff," said Elton. "But our overwhelming [population] is students, where we're an ISP. We don't have any control over what [device or card] they use or what software they run, so ability to look at their bandwidth will be a big help."

Existing HiveAP performance reports can graph per-AP or per-station throughput. Performance Sentinel goes further by tying measurements to per-station demand and goodput targets defined for each user. Monitoring transmit queue depth and aging on HiveAPs, Performance Sentinel generates a compliance violation if Service Level Agreements (SLAs) are not met during ten-minute windows. Thus, only clients that fail to meet SLAs and have more traffic they'd like to send trigger a violation.

Compliance violations for the entire WLAN are aggregated by HiveManager using a "compliance dashboard"—a summary that uses a pair of 24-hour graphs to depict percentage of non-compliant APs and clients. Those summary graphs are followed by a list of non-compliant (red) or boosted-to-compliant (yellow) devices, allowing one-click drill-down into station or AP details.

Adam Conway, vice president of product management, said customers should set user profile SLAs to the minimum goodput required to be successful. "We recommend turning on monitoring first," said Conway. "If you're seeing a lot of red, evaluate whether you need more APs, whether you need to migrate old devices to 802.11n, or whether you need to adjust your SLAs."

For example, a laptop sending e-mail and Web traffic might require 2-3 Mbps, while a medical device uploading large images might require 6-10 Mbps, in short bursts. Most APs are over-subscribed to support all kinds of clients, since all are not simultaneously active. To manage AP and RF resource allocation, customers can apply existing QoS measures like WMM priorities, weighted traffic queues, and bandwidth limits. SLAs complement those controls by letting admins easily determine whether stated goals are actually being met for each and every user.

"We've had a lot discussion with customers about whether they can replace cables in cubicles with Wi-Fi," said Aerohive's vice president of marketing Stephen Philip. "They say that, with wires, they can define SLAs and measure whether they're meeting them. They need that same level of determinism and visibility with Wi-Fi too."

Proactively preventing problems

As many dorm dwellers can attest, it's no fun to have a thermostat that reports chilly room temps without being able to turn up the heat. That's where Airtime Boost comes in—when Performance Sentinel flags a violation, that client can receive extra airtime in hopes of meeting its SLA without putting a damper on anyone else's goodput.

Airtime Boost applies the real-time channel utilization and allocation technology that Aerohive developed for Dynamic Airtime Scheduling (see our review). Dynamic Airtime Scheduling adjusts transmit opportunities to give everyone their fair share of the channel. Airtime Boost goes further by letting customers dictate how airtime should be divvied whenever resources fall short.

"Dynamic Airtime Scheduling optimized throughput for the entire network," said Conway. "With Airtime Boost, if some slower clients fall below their [SLA], they can now get corrected by adjusting airtime scheduling. This is just the first action that we'll be able to take; we expect to add other mechanisms in future releases."

For example, consider three 802.11g clients that should receive at least 6 Mbps each; all others are guaranteed 2 Mbps. If six clients are simultaneously active with Dynamic Airtime Scheduling on, all will achieve the near-theoretical max 5.5 Mbps. When Airtime Boost is also enabled, those three clients will be granted extra airtime to reach 6+ Mbps apiece. This action will, of course, diminish the throughput experienced by other clients, but not below their designated SLAs—unless the total offered load is consistently higher than the AP's capacity.

Elton is intrigued by Airtime Boost, but frankly more excited about Performance Sentinel. "If we found that 80 percent of our clients were okay, we might boost the other 20. We'd like to help students with slower laptops and antiquated cards do a bit better," he said. With Airtime Boost, this could be attempted without robbing clients that have strict higher-priority SLAs, like the wireless ticket scanners at the college's athletic fields.

The fine print

Performance Sentinel and Airtime Boost are the biggest news in Aerohive's upcoming 3.4 release. These inter-related HiveOS features can be used by customers that manage small WLANs using HiveUI only. However, the highly-visible Performance Sentinel compliance dashboard is only available when HiveManager is used for centralized WLAN monitoring and reporting.

These new features—and other 3.4 enhancements like Wireless VPN (IPsec tunneling of user traffic exchanged between HiveAPs)—will ship mid-October. Beta customers have not yet road-tested 3.4, but all Aerohive customers will get a chance to do so when they receive these standard HiveOS features at no additional cost.

"Performance Sentinel and Airtime Boost will let IT, for the first time, establish, monitor, and deliver throughput guarantees for individual Wi-Fi clients," said Philip. "We think these kinds of capabilities are essential for Wi-Fi to achieve its potential as an Ethernet replacement."

Lisa Phifer owns Core Competence, a consulting firm focused on business use of emerging network and security technologies. A 28-year networking industry veteran, Lisa has been involved in the design, implementation, and testing of wireless products and services since 1996.



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