Smarter Celeno Wi-Fi chip manages device throughput

What if your home Wi-Fi router could juggle all your smartphones, tablets, laptops, consoles and the rest of your technostuff, weigh the different types of traffic, and then make adjustments to optimize throughput for each device? New firmware for Celeno Communications' Wi-Fi chips is intended to do just that.

The new OptimizAir 2.0 code is for what Celeno calls "airtime management." It now lets the Celeno 11n and 11ac radio chips use customized rules to allocate to each SSID (or even each device) set up on a router or similar device a specific amount of time for its transmissions. Throughput is directly proportional to time on the network. OptimizAir makes transmission time consistent for clients, smoothing out network connections, and making it impossible for one client to hog the air, crippling throughput for the others.

This idea of "airtime fairness" isn't new, but Celeno is introducing this capability on its radio chip, not as a higher layer software feature as has been typically done by WLAN product vendors.

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Celeno's chips are aimed at home gateways and routers and similar network infrastructure devices, often supplied via a cable TV company or Internet provider. Using the new firmware, they could, for example, add a second SSID for public Wi-Fi access to the residential wireless router offered to residential customers. With OpitmizAir 2.0, the provider can allocate 80% of the capacity in a given channel to the residential Wi-Fi clients, and 20% for the outward-facing public Wi-Fi access, says Lior Weiss, vice president of marketing for Celeno, in Ra'anana, Israel.

Celeno was founded in 2005 to create Wi-Fi chips for home wireless networks. The goal was to create chips that wirelessly distribute several high-def video streams at the same time throughout a home. Today, the chips are used by more than 75 service providers in the wireless routers and gateways they provide their residential customers. Investors include Cisco, Greylock IL Partners, Liberty Global and others.

Wi-Fi is a collision-based protocol, Weiss points out, with the air as the transport medium. "The scarcest resource is access to the air," he says. Regardless of how many clients associate to it, any access point "converses" with only one at a time. As the number of clients increase, "typically the access point struggles with allocating enough time to serve them all," Weiss says. "You end up with sub-optimal throughput for some clients."

"Depending on the application layer and streaming protocol, you can have cases in which clients with a poor signal are hogging the air," he says. "You may be watching your Netflix movie on your tablet, just three meters from the access point, but an iPhone outside your house, with one antenna, logs in. It can end up comprising the tablet."

With OptimizAir, the Wi-Fi radio chip is no longer a passive provider of access: it can enforce pre-provisioned rules, based on a range of criteria, to restrict clients to a window of  transmit time. "You can adjust this time bucket' in real time to deliver specified throughput" for each client, Weiss says.

How this capability will be applied is unclear, because it hinges on what the service provider priorities are, and their assessment of how to optimize the wireless experience for their customers.

Weiss thinks that these providers are likely to use the new OptimizAir capability to create two or more SSIDs for a given Wi-Fi access point and, within each SSID, a "hierarchy" of client devices. One SSID might be reserved for home automation sensors, another for the provider's Wi-Fi enabled set top box, another for a public Wi-Fi hotspots. Initially, the airtime/throughput tradeoff could be "set in stone" with specific allocations for each SSID. That could be expanded to specific allocations for different classes of devices.

"I envision that the time is divided evenly," Weiss says. "This alone will take you a long way. Today, the strong clients are killing the clients farther away. Sometimes it's vice versa. It's never balanced out and this balances it out."

The concept of airtime fairness in Wi-Fi is not new, as Weiss acknowledges. WLAN vendors have focused on it as a way to improve client performance. The idea is to collect more information about, and from, Wi-Fi clients, and then use an array of techniques and clever tricks to let the network exercise more control over the vagaries of client wireless behaviors. In some cases this has meant shifting clients from one frequency to another, or to a less loaded access point.

Aerohive, Aruba, Cisco, Meru and Motorola, to name just a few all offer some form of airtime management, as Network World's Wireless Alert blogger, Joanie Wexler noted in a 2009 blogpost

"[T]hey dynamically determine the exact amount of airtime each client is consuming in microseconds," she wrote. "They then adjust the number of opportunities each client gets to transmit, using algorithms that account for each client's characteristics, such as current throughput, distance from the AP and even 802.11n's comparative efficiencies such as packet aggregation and 40MHz channels. The primary goal is to ensure that the slowest client doesn't set the pace for all clients on the network and monopolize the air."

Broadcom promotes "airtime fairness" as a feature of its enterprise-focused, 802.11ac BCM43460 system-on-chip, first announced in early 2012 for release in the second half of that year.

Celeno's OptimizAir 2.0 firmware is sampling with customers now.

John Cox covers wireless networking and mobile computing for Network World.Twitter: http://twitter.com/johnwcoxnwwEmail: john_cox@nww.com

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