US Robotics 802.11g Wireless Turbo Multi-Function Access Point

Price: $249.95

: 802.1x and SNMP support, excellent performance with native clients
Cons: Pricey, no WPA (yet)

Reading the packaging and various materials that come with the new US
Robotics Wireless Turbo Multi-Function Access Point
, you might be forgiven
to think that the product was the best thing to happen to wireless since the
invention of AM radio. With copious use of terms like "100% faster",
"100 Mbps", "Turbo", and "Accelerator" the claims
seem audacious even by marketing standards.

The main claim to fame of the 5450 is that it’s one of the first products to
utilize the new TNETW1130 802.11g chipset from Texas Instruments <QUOTE NYSE:TXN>.
After nearly nine months of 802.11g product availability and over three months
after the standard was ratified, yet another 802.11g chipset would seem to be
a yawn inducer. What’s supposed to make this particular slab of silicon noteworthy
is the fact that it’s the first 802.11g product with native support for Packet Binary Convolutional
(PBCC) modulation, the technology used in 22 Mbps (802.11b+) hardware.
TI had lobbied unsuccessfully to have PBCC modulation included in the final
802.11g standard, but it was defined as an optional modulation technique.

The "Turbo" refers to TI’s packet aggregation mode, which aims to
improve performance by streamlining the transmission of packets. The frame bursting
feature of previous chipsets aim to improve performance by sending more than
one packet before requiring an acknowledgement by the recipient. The TI approach
optimizes throughout by combining multiple packets in to a larger packet with
a single header, thereby reclaiming some of the bandwidth consumed by network
overhead and putting it to use moving actual data. It’s a different means to
the same end.

But what about claims of "100 Mbps" and "100% faster"?
Read on to see if the product lives up to its boasts.

The $209.95 (street price) USR5450 is housed in a diminutive black plastic
case. With its low profile and extremely tall antennae, the unit almost has
a Bugs Bunny look to it. The 5dBi diversity antennae are of the tilt and swivel
variety, removable via reverse SMA connectors.

Like many previous US Robotics (USR) products, the USR5450 has a 9-pin serial
port on the rear of the unit for direct configuration. In addition to the obligatory
browser-based configuration method, you can also access and modify the unit
via Telnet. On my test unit, the AC adaptor plug fit into the USR5450 very poorly,
and in fact came loose on more than one occasion. Hopefully, this was a peculiarity
rather than a widespread phenomenon.

Most people will likely utilize the USR5450 as straightforward access point,
but the unit is versatile enough to function as a bridge, repeater, or even
as a client adapter, though I didn’t operate the unit in any of these modes
since I had only a single unit.

To pick nits for a moment, as someone who hails from the "red lights are
bad" school of technology, USR’s use of red LEDs (on both the AP and the
client card) to indicate normal function is mildly annoying and often still
makes me do a double take.

The initial setup of the USR5450 didn’t go as smoothly as I would have hoped.
USR supplies a configuration utility to locate the access point on the network,
but as fate would have it, the software was unable to locate the device on two
separate systems and networks, even though it was powered up and properly connected
to the network.

The product documentation, which is HTML-based and somewhat difficult to negotiate
quickly (a PDF file would have been preferred), did not contain any information
about a default IP address for the USR5450. After a few minutes, I discovered
that the device was a DHCP client by default, and identified the address it
had obtained by checking the assigned address pool on my DHCP server. All’s
well that ends well, but I wonder how a user might reconcile a similar situation
if there was no DHCP server in place, since the unit doesn’t configure itself
to a static IP in the absence of DHCP. In this scenario, the utility would be
only way to access the unit.

Once you get to it, the USR5450 sports the same clear and functional interface
US Robotics has used in its previous products. Finding and modifying configuration
parameters can be accomplished quickly and easily.

The 5450 provides WEP encryption, and like previous TI-based products, it offers
a 256-bit WEP level in addition to the typical 64-bit and 128-bit varieties.
For now, WEP is the only way to go–WPA is under development, and is expected
to be available in the October 2003 time frame. USR will submit the USR5450
for Wi-Fi certification at that time. Client authentication can currently be
done by MAC filtering or via 802.1X with external RADIUS server.

The product provides a rather unique security feature that can be used in association
with MAC filtering function. It has a "WARN" LED on the front bezel,
which can be configured to illuminate whenever a client with an unauthorized
MAC address attempts to associate to the access point. The rationale to provide
some kind of visual indication that mischief may be afoot seems reasonable (and
the light did flash when my "rogue" client attempted to connect).
On the other hand, without an audible warning you have to be looking at the
light to notice it, and it could just as easily be set off by passers-by who
aren’t necessarily attempting mischief, but simply have SSIDs set to "ANY."

On the subject of monitoring, there is a device log, but since it exists only
in volatile memory (it can’t be output to a file or to a Syslog server) its
usefulness is limited. Thankfully, the USR5450 does provide SNMP support for
remote monitoring.

The USR5450’s radio offers six levels of transmission power ranging from "highest"
to "lowest." The fact that "medium high"– the third level
— was the default setting immediately caught my attention. USR told me that
this feature is currently disabled, and that by default it transmits at its
full 100mW signal strength. The power levels will be implemented in a later
firmware release.

When it came to performance, the unit performed well in some scenarios and
not so well in others. One thing is for sure–no reasonable interpretation of
the results can let one to believe that it delivers performance equivalent to
100Mbps, or that its 100% faster than the competition.

G-only mode Chariot performance testing
on the 5450 revealed results that were within range of products based on competitive
chipsets. In native mode with a USR 5410 PC Card client adapter for example,
the USR5450 exhibited throughput of 20.67Mbps at 10 feet, which dropped to just
under 9Mbps by 125 feet. Enabling the "Turbo" packet bursting mode
(on both the AP and the client) did improve performance measurably. With the
feature turned on, peak throughput at 10 feet rose from 20.67 to 26.52 Mbps,
an improvement slightly more than 25%.

On the other hand, during distance testing the USR5450 exhibited an odd performance
characteristic at ranges beyond 25 feet. In these tests, the throughput levels
as plotted by a Chariot graph resembled a compressed sine wave, with the throughput
alternately rising and dropping substantially at almost exactly at two second
intervals, about 30 times over the course of the test. This phenomenon exhibited
itself at only at distances beyond 25 feet, which happens to be the approximate
point in my environment where line-of-sight with the access point is lost.

Re-orienting the 5450’s antenna or the unit itself sometimes reduced the effect,
but it didn’t eliminate it entirely. Observing the client during the test indicated
that the signaling rate did fluctuate at times, but not in a pattern that correlated
to the Chariot graph. This behavior was not displayed by other 802.11g products
I’ve recently looked at.

The volatility of the USR5450’s throughput rate did have a clear impact on
performance, but since it was transmitting at a high rate through most of the
test it suffered only about a 15% throughput penalty as a result of the fluctuation.
Typically, the existence of persistent interference would cause an access point
to consistently operate at a lower rate or perhaps adjust the rate as conditions
varied, but these results still suggest that the USR5450 may have difficulty
maintaining a consistent signal quality at distance in some environments. USR
wasn’t able to induce the same behavior.

In the mixed mode test, the access point produced throughput of 10.31Mbps for
an 11g client with a 11b client associated. That figure jumped to 17Mbps with
Turbo mode enabled, an increase of almost 70%. A run with 11b and 11g clients
transmitting simultaneously dropped aggregate throughput to 7.96Mbps (with 5.27Mbps
for the 11g client and 2.71 for the 11b client). These results certainly didn’t
represent the best throughput among 802.11g products, but neither are they the
lowest. Enabling the Turbo mode in this scenario improved total throughput to
11.7Mbps, and gave the 802.11g client a big boost to 9.72Mbps. The 802.11b client
throughput in turn dropped slightly, to 2.05 Mbps.

Since one of the purported benefits of the TI chipset is compatibility with
the 22Mbps signaling rate of 802.11b+ clients, I did an additional run substituting
a TI-based 802.11b+ client for a conventional 11 Mbps client. In this test,
aggregate throughput rose from 7.96Mbps to 9.60Mbps. And while the throughput
rate for the 11g client climbed only slightly, to 5.82Mbps (from 5.27), the
11b+ client fared well with 3.81 Mbps of throughput, compared to the 2.71 the
b client had posted.

My final test was to remove the 802.11g client and run the 802.11b+ client
alone (again with 4x enabled). In this case, it actually posted throughput numbers
in excess of 10 Mbps. That’s almost twice what the b+ client would be expected
to do while connected to a native 802.11b+AP, indicating that the 5450 can breathe
new life into older PBCC clients.

Attempts to associate a non-TI 802.11g client to the 5450 went off without
a hitch, and the client (in this case, and Intersil-based card) performed comparably
to the TI client with Turbo mode inactive.

USR touts the TI chipset’s ability to provide superior performance and support
the widest variety of clients at their native signaling rates. In actuality,
while TI-based 11b and 11g clients can benefit greatly from Turbo/4x mode, the
test results suggest that when this mode is not used, the 5450 doesn’t provide
any better performance for 802.11g and plain-vanilla 802.11b clients than access
points based on other chipsets.

Features of the USR5450 like bridging, repeating, and 802.1x support (and soon
WPA) compare favorably with most of its peers, and the performance benefits
of the Turbo mode are clear. Therefore, if you’re starting a WLAN from scratch
and plan to stick with TI-based hardware, or if you want to gradually upgrade
to 802.11g technology but still have a large installed base of TI-based 802.11b+
clients that you want to take full advantage of, then the US Robotics 5450 is
clearly a good choice.

On the other hand, non-TI clients won’t be able to reap the performance rewards
of the 5450’s Turbo mode. This fact, combined with the product’s very high $200
street price makes it a less compelling purchase in many cases. If you don’t
have a significant investment in existing PBCC hardware, you will likely find
an equally capable access point at a lower cost. A lower price, better documentation,
and the inclusion of WPA support, would tip the scales towards the 5450’s favor.

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