Access point with redundancy and load-balancing features

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, i.e., 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 per cent, and then at low signal strength,

which was between 15-20 per cent. 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 per cent improvement over a 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 access point to a distance

where the signal strength dropped to 15-20 per cent. 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.