Old-school Wi-Fi is slowing down networks, Cisco says
By Stephen Lawson
The early Wi-Fi standards that opened the world’s eyes to wire-free networking are now holding back the newer, faster protocols that followed in their wake, Cisco Systems said.
The IEEE 802.11 standard, now available in numerous versions with speeds up to 6.9Gbps (bits per second) and growing, still requires devices and access points to be compatible with technologies that date to the late 1990s. But those older standards—the once-popular 802.11b and an even slower spec from 1997—aren’t nearly as efficient as most Wi-Fi being sold today.
As a result, Cisco thinks the 802.11 Working Group and the Wi-Fi Alliance should find a way to let some wireless gear leave those versions behind. Two Cisco engineers proposed that idea last week in a presentation at the working group’s meeting in Los Angeles. Their plan drew some debate from others who expect a new wave of low-power Wi-Fi gear to emerge for the so-called “Internet of Things.”
The plan is aimed at making the best use of the 2.4GHz band, the smaller of two unlicensed frequency blocks where Wi-Fi operates. It doesn’t affect the 5GHz band, which most modern Wi-Fi gear can use in addition to 2.4GHz. (The latest standard, 802.11ac, works exclusively in 5GHz.) The 5GHz band has more available bandwidth and also is less crowded, while the lower frequencies are sometimes called a “junk band” because so many devices use it for Bluetooth, baby monitors and other technologies in addition to Wi-Fi.
One of the main reasons 2.4GHz has a bad reputation is traffic sent using old, slow forms of Wi-Fi, according to Brian Hart, a principal engineer at Cisco, who gave the presentation with fellow Cisco engineer Andrew Myles. That happens partly because of outdated code written back when early Wi-Fi versions were more prevalent, and partly because of IEEE and Wi-Fi Alliance requirements for supporting the lower rates, he said.
Wi-Fi emerged in 1997 with a data rate of just 1-2Mbps. It got a speed boost a few years later with 802.11b, which offered as much as 11Mbps and helped make Wi-Fi a hit. But those standards were left in the dust by 802.11g, with 54Mbps, and 802.11n with as much as 600Mbps. The latest Wi-Fi standard, 802.11ac, goes into the gigabit range. (All these are theoretical speeds, so users get something less in real life.)
But as new versions of Wi-Fi came along, they didn’t replace the old ones. Instead, new products have to support all the preceding standards, too. Specifically, they have to be configured out of the box to find other Wi-Fi gear that may be using the old technology. That requires sending packets out at slow speeds, all the way down to that old 1-2Mbps rate.
The slower wireless data traffic is, the longer it occupies the channel it’s using. So older forms of Wi-Fi hold onto channels a lot longer than the new ones do. This is especially a problem in 2.4GHz, the only band that the early versions can use, because there are only three non-overlapping channels available there. In some cases, modern Wi-Fi traffic can’t reach its speed potential partly because it has to wait in line behind slower packets going out to find old gear, Hart and others say.
This is one of the culprits in wireless woes at large public venues such as stadiums, according to Hart.
“The reason it doesn’t work is actually [that] a very large proportion, half the traffic sometimes, can be these 1Mbps packets,” he said.
The problem is, there’s not much Wi-Fi gear today that needs lower rates, Hart said. Most of that slow traffic is from devices probing for antiquated networks they’ll never find, according to Hart.
Wi-Fi rules require a default setting of probing at 1Mbps, but users can turn it off, Hart said. In fact, Cisco recommends its customers modify their products to probe at no less than 6Mbps or 11Mbps, he said.
Now, Hart and Myles are proposing to make the low data rates optional.
They say they aren’t suggesting the removal of 802.11-1997 and 802.11b from the IEEE standard. Instead, they’re proposing changes that would allow for two certification tracks at the Wi-Fi Alliance. One track would hold on to the slower speeds, while the other would gradually discourage the use of the older modes. Hart and Myles refer to the new approach as a “green” certification, saying the slow probe traffic acts like pollution in the 2.4GHz band.
To keep the change gradual, the “green” certification would actually start out with slow rates mandatory. Later, they would be optional, and eventually, vendors would have to leave those old protocols out of their products to earn the “green” certification.
Not so fast, say others in the Wi-Fi world.
”I want to make sure that when we deploy an Internet-of-things type device in the future, that it can rely on the fact that the infrastructure can support its transmissions,” said VK Jones, vice president of technology at Qualcomm Atheros. His company is a major Wi-Fi silicon vendor and a subsidiary of Qualcomm, which supplies many of the chips in phones and tablets and is looking to other small connected devices for future growth.
Jones thinks the Internet of things, which may include smart electric meters, environmental sensors, health monitors and many other small, low-power devices, represents a growing class of devices that will often make use of very low Wi-Fi data rates. Range will be the key reason for this, he said: Most such connected devices will have faster standards such as 802.11g built in, but they may be so far from the nearest access point that 1Mbps is the only available rate.
For example, a smart power meter installed on the far end of a house may have to go through several walls to get to the home’s Wi-Fi Internet gateway, he said. A 1Mbps rate may be the only option for achieving that distance.
“You can rely on the fact that the infrastructure today in the home supports 1Mbps. We’d lose something powerful about Wi-Fi that we have today if we eliminated that,” Jones said.
The Hart and Myles proposal suits the enterprise market that is Cisco’s bread and butter, he said. In offices, range is less important than capacity, and the newer wireless LANs being used in enterprises have access to the 5GHz band and its riches of additional spectrum uncluttered by 2.4GHz-only devices, Jones said. But not all Wi-Fi fits that profile. “We need to take into account all market segments,” he said.
Jones was there for Hart’s presentation and brought up his objections there. “We had a nice discussion about it,” he said, adding that he and Hart are friends.
Hart presented the idea in the 802.11’s Maintenance Task Group, which addresses technical issues not covered by the special groups that craft new standards such as those that periodically boost the speed of Wi-Fi. The next step will be for members to check within their companies to find out who may want to continue using older protocols. Members of the Maintenance group are now due to exchange comments on the plan. Hart hopes to have those comments resolved by July.
The two sides aren’t necessarily on the brink of a standards war. Both Jones and Hart are in favor of approaching the Wi-Fi Alliance for its help in addressing the issue. Jones said there may be new ways to address the lower rates but that it’s important to know what the current and future markets for those technologies look.
”What we’re not open to is being hasty and to putting in motion a series of events that has these important modes not available any longer,” Jones said.
Some industry analysts think the time has come to move on.
”If you look at especially public-access hotspots, the rationale for providing that backwards compatibility gets a little thin,” Yankee Group analyst Ken Rehbehn said. “People generally upgrade their devices every two years.”
”Older technologies really should be phased out over time,” said Craig Mathias of the consulting company Farpoint Group, which recommends not buying Wi-Fi products that don’t have at least 802.11n. One benefit to letting vendors leave out the earliest Wi-Fi protocols might be simpler and less expensive chips, he said. “I think in general, we would see some benefit from this,” Mathias said.
However, there are so many types of devices vying for bandwidth in the 2.4GHz band that there’s no guarantee Cisco’s proposal would make life much better there, he said.
With a long standards process ahead, it’s unlikely users would see any benefit from such a plan for at least three years, Mathias said. Wi-Fi is still usable in both of its bands, but taking some action might be a good idea, he said. “This is not a critical problem. It’s a looming problem.”
This article was updated on January 29 to correct a statement about 802.11ac working exclusively in 5GHz.
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