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Co-channel interference

While 802.11a/b/g stations connect to APs at data rates anywhere from 54 Mbps down to 1 Mbps, when the network is properly designed, data rates are kept as high as possible.  It's important to consider, however, that just because the slowest client might be connected at 12 Mbps in a cell, that doesn't mean that the RF signal just stops right there at that client.  On the contrary, the signal keeps going well past where a user might connect at 1 Mbps.  Even at this great distance from the AP, the RF energy is strong enough to cause clients to defer transmissions due to "busy" clear channel assessments.  This distance might be hundreds of feet indoors, depending on the environment.  In addition to the energy emitted by AP transmissions, one must consider the energy emitted by client transmissions as well.  Clients move away from APs while transmitting, and thus cause co-channel interference at a much greater range even than the AP can cause. 

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Architecture Naming

There are two distinct types of architectures in today's WLAN infrastructures.  Each goes by several different names.  Today's WLAN newcomers can be easily confused by having several names for the same thing as well as trying to understand the nuance between each vendor's implementation.  I'd like to clarify some common terminolgy. Continue reading...

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Useability

What good is a piece of networking equipment if the end user can't effeciently operate it?  By 'operate' I mean install, correctly configure, and make on-going changes to. Hardware and software platforms in the WLAN industry have grown outrageously complex trying to meet the ever-growing demands of today's enterprise.  Sometimes organizations buy equipment based solely on specs, and soon thereafter develop a serious case of buyer's remorse due to useability problems.  Let's take the WLAN controller as an example.

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802.11n: 5 Reasons to Go For It!

1.  The technology works.  

With all of the vendors racing to be first, there's already a significant number of successful enterprise 802.11n deployments that prove that the technology actually works.  This is, of course, on top of all of the certification testing completed by the Wi-Fi Alliance.  I've tested a number of client adapters (Mini-PCIe, CardBus, USB, etc) and a small number of enterprise 802.11n APs.  They work.

 

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802.11n and Indoor Mesh

I was just sitting here reflecting on 802.11 indoor mesh networks.  The main problem with using mesh nodes (those APs that are connected to the network wirelessly) is the degraded throughput for client stations.  When stations transmit to the mesh node, it has to repeat the traffic to its upstream mesh node.  This continues until the traffic arrives at the mesh portal - an AP connected to the wired infrastruture.

 

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802.11n: The Top 5 Reasons To Wait

Trust me, there are many reasons to wait.  I just thought I'd share a "quick 5" with you.  I've been playing with 802.11n gear now for quite a while, and I deal with these issues quite a bit.  I've been talking to quite a number of people about the "why / why not" of 802.11n implementation, and here are some that are pretty common.  Enjoy.

 

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802.11n Upgrade: AP Substitution. Is it viable?

I'm sure that by now you've read the early 802.11n deployment documentation by various vendors.  It's pretty much a consensus in these documents that there are a small set of ways to deploy an 802.11n upgrade to an 802.11a/g network.  As a precursor, it is highly recommended by most vendors to use 5 GHz for the bulk of 802.11n deployments due to more available channels and bandwidth. Continue reading...

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802.11n Line Rate vs. Data Rate - Part 1: Frame Aggregation

Although the PHY layer enhancements (such as MIMO, 40 MHz wide channels and short guard intervals) introduced in 802.11n improve the maximum line rate1 by more than 10x, the MAC layer enhancements (such as frame aggregation) are absolutely essential to achieving data rates that are anything close to the line rate. In this first article, we will briefly examine how data rate (802.11 throughput) is increased by MAC layer enhancements, in particular, we will look at frame aggregation. Without this 802.11n feature, it would not matter what line rate the physical layer achieves – the maximum data rate would be capped by overhead. Continue reading...

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Open Source WLAN Controller?

Have you ever seen DD-WRT?  How about SVEASOFT?  Perhaps WiFi-Box?  No, well they've been around for quite a long time, and they are organizations taking advantage of Linksys open source code for WLAN routers such as the WRT54G, WRT54GL, and WRT54GS.  These organizations take the source code for these units, provided by Linksys, and pack an amazing set of additional features into a somewhat unassuming piece of hardware - all for cheap or free.  Cool.  "So why does that matter to me?" you ask? Continue reading...

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Spectral Masks and Interference

The 802.11n draft 2.00 document defines both 20 and 40 MHz spectral masks. A transmit spectrum mask is the power contained in a specified frequency bandwidth, and regulatory bodies such as the FCC (United States) regulate how much power can be emitted from a transmitter at the center frequency and at given frequency points (called offsets) on both sides of the center frequency.

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