Making Sense of Evolving WLAN Standards, Part 2: Radios and Centralized Architectures

Despite the fact that the biggest obstacle to WLAN deployments in the enterprise
— security — is actively being addressed by new protocols like WPA, enterprises
are still wary of Wi-Fi.

According to IDC, a market research firm,
the consumer market continues to be the driving force behind Wi-Fi. IDC argues
that although Wi-Fi is catching on with highly mobile road warriors, general
business use of Wi-Fi, especially within the confines of the physical enterprise,
is lagging well behind home use. However, IDC is optimistic, noting that as
mobile workers become increasingly dependent on electronic forms of communication,
user demand and potential increases in productivity will drive businesses to
implement wireless networks.

ForceNine Consulting seconds this notion,
saying "purchases of WLAN hardware from large U.S. private and governmental
enterprises will exceed purchases from households and small-office/home-office
entities (SOHOs) for the first time in 2005." ForceNine projects that North
American enterprise WLAN purchases will reach one billion dollars by 2005, with
annual WLAN spending per enterprise employee reaching nearly $13 by 2005.

But ForceNine also sees excessive caution when it comes to enterprise commitment
to wireless. "In a recent survey we conducted of more than 50 enterprise
CIOs, we found that most large enterprises have either not yet deployed WLANs
or have committed only to small pilot deployments," said Dr. Sam Book,
a partner at ForceNine. "Once enterprises begin to better understand wireless
security, they will be more likely to embrace real enterprise-scale roll outs.
However, when security fears are assuaged, other issues will emerge, such as
evolving radio standards and equipment interoperability."

Choosing the Right Radio Standard

For those intrepid enterprises willing to take the wireless plunge today, the
first decision they must make is a relatively simple one: determining what flavor
of 802.11 they want to deploy.

802.11b clearly has the early momentum, offering throughput of 11 Mbps in the
2.4 GHz band over a 100-foot-radius footprint. For the reasonable future, 802.11b
should be sufficient for most of the tasks mobile employees need to do, such
as checking e-mail and accessing presentations, documents, and the Web. When
cost is added to the equation, 802.11b equipment, which is quickly becoming
commoditized in regards to APs and nearly ubiquitous in laptops, looks even
more appealing.

Looking ahead a few years, as deployments evolve from the pilot to the enterprise
level, 802.11b’s throughput may not be enough, especially if a large user base
begins seeking untethered access to next-generation applications like voice
over WLAN and mobile videoconferencing. For cutting-edge enterprises, 802.11a
makes more sense. It offers throughput of up to 54 Mbps in the less crowded
5 GHz band, while providing twelve non-overlapping channels vs. only three for
802.11b.

In November, the FCC sweetened the 802.11a pot by releasing an additional 255
MHz of spectrum in the 5.470-5.725 GHz band for unlicensed wireless devices.
This increases the spectrum available to 802.11a devices by nearly 80%. Part
of the reason the FCC freed up the spectrum was to harmonize the spectrum available
for unlicensed devices throughout the world.

"The bottom line, from a customer standpoint, is that with 802.11a users
gain more channels, and their equipment will still work as they travel to different
countries," said Paul DeBeasi, vice president of marketing at Legra
Systems
, a provider of WLAN switches.

While several companies, most notably Intel , have been talking up the
many advantages of 802.11a — despite the fact that Intel has yet to deliver
802.11a chips, but that’s a separate story — yet another 802.11 variant hit
the market with a bang last year: 802.11g. Offering the same 54 Mbps of throughput,
the main advantage of 802.11g over 802.11a is that it operates in the 2.4 GHz
band and was designed to be backwards compatible with 802.11b.

I asked DeBeasi which flavor of 802.11 he recommends. "That depends,"
he said. "Even though 90% of the installed base is 802.11b, customers prefer
a network infrastructure that supports all three types of 802.11." A multi-band
solution (supporting 802.11b/g and 802.11a) provides future-proof protection
by being more flexible than an 802.11b/g-only or 802.11a-only solution. "A
multi-band solution allows customers to design a network that supports all three
standards simultaneously," he said.

Considering that 802.11a and 802.11g offer the same amount of throughput, with
802.11g also supporting legacy 802.11b clients, why then would you still opt
for a multi-band solution? Isn’t 802.11g good enough? Not necessarily. The main
problem with 802.11g is that it still occupies that crowded 2.4 GHz band, which
must share space with such devices as microwaves and cordless phones.

"If you have any concerns about performance, or if you’re experiencing
a lot of interference with your 802.11b pilot project, then you’ll be best served
with 802.11a," DeBeasi said. In its relatively uncrowded band, 802.11a
has more channels than 802.11b, so it boils down to a simple choice," DeBeasi
added. "If you simply want wireless coverage as fast and as cost effectively
as possible and if you want to be able to communicate with the broadest set
of available client devices, then 802.11g is your best bet. However, if you
want a high-performance network, you need to factor in support for 802.11a,"
he said.

One drawback of choosing a multi-band infrastructure is cost. A multi-band
infrastructure will likely add as much as 20-30% to the initial cost of the
network. What an enterprise must consider, however, is if this initial price
premium will actually translate into long-term savings.

"We believe that any enterprise investing in WLAN technology would be
wise to invest in a multimode infrastructure," said Colin Macnab, VP of
Marketing at Atheros Communications, a
provider of multimode WLAN semiconductors. "You want to be able to serve
every available client, and, moreover, you need to be cognizant of the fact
that unlicensed wireless spectrum is an extremely scarce resource. Even if you
prefer 802.11a, you don’t want to just abandon the channels available in the
2.4 GHz band. As user bases grow, each available channel will be extremely valuable."

The Difficulty of Managing Access Points

The shift from consumer-grade to enterprise-grade wireless networking is being
driven by the new class of Wi-Fi switching devices. WLAN switches make it possible
to manage a large and distributed base of APs, but as these switches become
more common, a new problem emerges: how does your switch communicate out to
your many APs? Without a standard in place that facilitates this communication,
one of the main benefits of switch-based WLANs — the ability to build multi-vendor,
heterogeneous networks — is lost.

The leading candidate for standardizing switch-to-AP communications is the
lightweight access point protocol (LWAPP), which is currently going through
the process of becoming an Internet Engineering Task Force (IETF) ratified standard.
LWAPP centralizes many of the functions that now reside on the APs themselves.
"LWAPP goes a long way towards making APs, which until recently were consumer-class
products, suitable for enterprise deployments," said Alan Cohen, vice president
of marketing at Airespace.

With LWAPP in place, enterprises can secure and manage large WLAN deployments
as a single network, rather than attempting to manage a slew of individual APs.
LWAPP would allow WLAN system vendors to focus less on switch-to-AP access software,
enabling additional innovation in the higher-layer features, such as authentication,
packet filtering, and policy enforcement for a switch or router. Moreover, those
other higher-layer functions — including QoS, rouge detection, and load balancing
— can be centralized for an entire enterprise WLAN. A network manager can simply
install a WLAN switch in a wiring closet or in a data center, while relying
on LWAPP for AP device discovery. It doesn’t even matter if the APs are from
multiple vendors. LWAPP standardizes the communications between all of them.
With LWAPP running, the switch will automatically discover and integrate any
AP into the network, enabling large-scale, multi-vendor, heterogeneous networks.
"The major advantage of this," Cohen said, "is simply choice.
Customers always prefer having choices."

LWAPP, however, has its detractors. Cisco initially
supported LWAPP before doing an about face, and now Cisco is seen as one of
LWAPP’s principal opponents. According to Ron Seide, product line manager in
Cisco’s wireless networking business, however, this perception is exaggerated.
"We support some of the ideas behind LWAPP, but we’re more concerned with
other wireless LANs issues, most specifically the interoperability from the
AP out to client devices."

Seide said that it’s too early for Cisco to commit to any specific switch-to-AP
standard at this time. Cisco recently announced its own proprietary version
of LWAPP called the Wireless LAN Context Control Protocol (WLCCP). Cisco, however,
does not have plans to standardize this protocol.

Other vendors complain that Cisco too often pushes its own proprietary protocols.
In addition to WLCCP, Cisco has been advocating the Cisco Compatible Extensions
(CCX) program rather than putting any effort behind standards. Moreover, Critics
argue that the company intends to get chip and NIC vendors to add proprietary
features like LEAP security into their products, which, if successful, could
undermine the push for broader open standards.

Seide said that while Cisco is not opposed to standards, he’s not convinced
that APs should be "thinned" down, as LWAPP implies. "I would
argue that some functions are best located on the access points, such as port
blocking, and while I agree that you’ll see a thinning down of wireless domain
services on the AP side, you may see a fattening of other features like QoS,"
he said.

Seide argued that "fat" vs. "thin" isn’t really the issue
when it comes to the future of APs. "It’s not a problem of size, but flexibility.
Different settings will dictate different deployment strategies." He used
the example of an insurance agency. At the main office, a thin-AP strategy would
make sense, but out at a remote claims office, for instance, where there may
be less network support, more features would need to be resident in the APs
themselves.

The Future of Access Points

Of course, branch offices might best be seen as more accurately fitting into
the consumer/SOHO segment, rather than the enterprise market, meaning a different
class of equipment would suffice. When it comes to enterprise-scale deployments,
though, many companies, such as Legra, Airespace, and others believe that APs
must evolve. Whether far or thin, management features must be centralized.

"The only way enterprises will commit to large-scale WLANs is if they
have the ability to control those deployments from a single device. Without
centralized control over configuration, security, monitoring, and troubleshooting,
the enterprise is faced with a management nightmare," Legra’s Paul DeBeasi
said.

"You can separate what you need in a WLAN AP into two components, and
where those components reside is, to me, the crux of the debate," said
Scott Lindsay, vide president of marketing at Engim, a provider of multi-channel WLAN chipsets.
"First, there’s the intelligence component, the brain if you will. Whether
it’s in the AP or a switch, I believe you need some degree of centralization
to make your network manageable. Second, your wireless network needs sensors,
or the eyes and ears of your network, and this component must reside in the
APs. You could be fattening up the APs by providing additional sensing capabilities,
enabling your APs to take in the most amount of information about interference,
spectrum availability, and client types on the network, but you probably want
the network-level control in a different device. Does that mean these are thin
APs? I’m not sure that it does, because as more users enter the network, you’ll
need more radio-specific functionality available in the APs. From a networking
standpoint, though, the APs will almost certainly get thinner."

As companies like Engim and Atheros begin to provide advanced radio-management
features within the silicon itself, the APs based on those chips begin to look
thinner still. Legra’s DeBeasi takes the thin-AP argument a step further, arguing
that leaving networking functions on the APs could bog down the network. As
an example, he pointed to security, which resides on APs in traditional WLANs.

"We’ve pulled cryptography out of the AP because security standards are
changing so quickly. A centralized encryption architecture is much easier to
manage and upgrade. Access point-based cryptography is a legacy artifact from
SOHO-based products. We believe that WLANs will be heterogeneous from a security
standpoint for a long time to come, with WEP, WPA, IPSec, and eventually 802.11i
all running at the same time. So your network infrastructure has to evolve to
support that patchwork."

In essence, the only way to address these security issues in a manageable way
is to centralize Layer 2 security, Layer 3 security, and policy management in
a switch, otherwise critical security functions remain nearly unmanageable in
large deployments.

DeBeasi pushes the thin-AP argument even further: "I see radios becoming
essentially like intelligent antennas. They’ll be like light bulbs, cheap and
replaceable. Radios will get thinner, but they’ll have to be managed by other
intelligent devices. Before this can happen, though, there needs to be some
sort of protocol that enables APs to communicate back to centralized appliances."
Without such a standard, customers face a situation where they are locked into
equipment from only one vendor, with each vendor concocting various proprietary
protocols for AP-to-switch communications. Which brings us back to LWAPP.

Is Configuration Management a Looming Bottleneck?

While the Cisco worldview certainly can’t be ignored, especially since Cisco
is the leading WLAN equipment vendor by far, Legra, Airespace, and the other
switch vendors seem to be on to a very important point: once you have a standard
like LWAPP in place, then you have more flexibility in your AP deployments.
You can deploy a switch from one vendor and APs from others, and you can also
choose the latest AP for your network as it expands, rather than being locked
into your initial choice for compatibility’s sake.

All of this, though, depends on having a centralized network architecture.
Without a centralized control device, it is much more difficult to upgrade your
APs to a new security protocol, or any other protocol for that matter. Without
centralization, enterprises will be faced with a manual process when it comes
time to upgrade their installed base of APs.

"When vendors began to focus on the issue of configuration management
in wired networks, they built that capability into switches because switches
were the centralized resource," DeBeasi said. "In today’s small consumer
and SOHO environments, configuration management isn’t a big issue. In tomorrow’s
massive enterprise deployments, configuration changes could bring upgrades to
a grinding halt. When will network managers find the time to manually configure
all of those APs?"

Supporters of LWAPP, argue that this standard will make the problem of configuration
easier still. With the communications interface in place that allows switches
to communicate with APs, it becomes easier to layer features on top of that
basic communications layer, and, thus, it becomes easier to manage and configure
a large installed base of APs."

In essence, the key to keeping up with the shifting standards associated with
WLANs is to centralize them in order to manage them. This allows your network
to remain open and flexible without becoming chaotic and impossibly complex.
Moreover, your network has the ability to evolve as WLAN technology evolves,
rather than becoming obsolete the minute you deploy it. However, not all standards
can be relegated to the switch, of course. There has to be something residing
on both APs and client devices, but with a switch acting as the command-and-control
center of a WLAN, changes to any standard, even client standards, can eventually
be controlled and managed in a centralized, orderly manner. In a proprietary,
fat-AP world, the standards will do little to address the flexibility needed
to keep up with the latest trends in the rapidly evolving WLAN world.

Jeff Vance is a technology writer and consultant. He was previously the
editor of
Mobile Internet Times and E-Infrastructure Times, before
striking out as a freelance writer. He now focuses on high-tech trends in wireless,
next-generation networking, and Internet infrastructure. His articles have appeared
or are forthcoming in
Network World, Wi-Fi Planet, DeviceTop.com, SearchNetworking.com,
and Telecom Trends, among others. You can contact him at [email protected].

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