WIRELESS ACCESS POINT: D-Link DWL-1000AP+

A wireless access point extends your wired LAN to wireless users, but this access point from D-Link does much more than that. The device can provide five
functionalities. The first is the most basic one, that of an access point.
Second, it can work as a wireless repeater to increase the range of your
wireless network. Third, as a wireless bridge between two different wireless
networks. Fourth, as a multi-point wireless bridge between more than two
different wireless networks. And, fifth, in wireless client mode wherein it
works as a client of some other wireless network. But, you can use only one of
these functions at a time.

When working as an access point, it has an enhanced mode of operation wherein if it's used in conjunction with other enhanced D-Link wireless products, it will work at double the speed of regular 802.11b products, ie 22 Mbps (other 802.11b products work at 11 Mbps only).

All the above-mentioned features are also present in the device's younger cousin,
D-Link DWL-900AP+. However, D-Link DWL-1000AP+ differs by offering load
balancing and redundancy features. It can be used with other DWL-1000AP+
devices to create a load balanced wireless network. In this, all access points
will share the wireless traffic amongst themselves as the number of wireless
users increase. This way a particular access point will not run out of
bandwidth once the wireless user base in your organization grows beyond a
single device's capability. Redundancy feature works such that it can be used
as a backup access point for another DWL-1000AP+. So if the primary access
point fails, the second one will take over. The backup and primary access
points connect to each other via an additional Ethernet link provided on the
devices. These features can be useful when implementing a wireless network in a
large enterprise.

Coming to performance, we tested the throughput (raw data transfer rate), response time and streaming data rate between a wireless client and wired host, with the access point working as the communication link between the two. The wireless
client was a laptop containing an internal mini-PCI 802.11b card. We also
tested the access point with a D-Link 650+ Air Plus 802.11b PCMCIA card to
check the enhanced wireless mode, which promises to double the transfer rate.
The wired client was connected to the access point via a 100 Mbps switch. We
used NeIQ Endpoint, Ixia Chariot Console, and NetIQ Qcheck for the tests. We
tested at two wireless signal strength levels. First, at high signal strength,
which was between 90-100%, and then at low signal strength, which was between
15-20%. Low signal strength obviously yielded lower performance as compared to
high signal. The high signal strength was done keeping the clients in line of
sight of the access point, while there were obstructions in the low signal
test.

With a non D-Link wireless card, at high signal strength, the maximum and average
throughputs achieved were 5 Mbps and 4.3 Mbps, respectively. With the D-Link
Air Plus card these increased to 7.6 Mbps and 7.0 Mbps, respectively. So, while
you would expect to achieve the theoretically possible transfer rates, in real
world usage, what you get is much less. But still the D-Link wireless card
managed a 50% improvement over the normal card, which can be attributed to the
enhanced mode of operation available in some D-Link products.

Next, comes the response time which measures the latency in the network. The average response time between the wireless laptop and wired desktop was 3 millisecs, which is fairly good. It even improved to 2 millisecs with the D-Link wireless
card. Finally, we have the streaming test, which checks the network's ability to
transfer a continuous stream of data at a particular rate. This is useful for
applications such as video conferencing and audio and video streaming. In the
UDP streaming test, the maximum achieved streaming data rate was 490 kbps,
which is also on the lower side but good enough for most streaming
applications. With the D-Link card it went up to 590 kbps.

After this we moved the laptop away from the aAccess point to a distance where the signal strength dropped to 15-20%. With the regular wireless card, the maximum and average throughputs achieved here were 0.983 Mbps and 0.360 Mbps. So the data
transfer rate decreased significantly with the decrease in the signal strength.
The response time also increased to move between 20-25 millisecs, which means
increased latency in the network. The maximum streaming rate here was 246 kbps,
which surprisingly is not very bad. Overall, an access point with features
suitable for enterprise needs and is also priced well.

Anoop Mangla

source: PCQuest