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SETTING MINIMUM DATA RATES? – READ THIS FIRST.

SETTING MINIMUM DATA RATES? – READ THIS FIRST.

  Nowadays when you speak with a WLAN professional you will often hear the suggestion of setting or restricting minimum PHY rates to optimise your WLAN’s  performance.  Many professionals nowadays consider this to be one of the basic tasks that must be completed in the process of configuring and optimising a WLAN. Configuring the minimum rates in a WLAN can have many benefits to your network’s performance including reduction of management overhead, removal of unnecessary RTS/CTS frames, better airtime utilisation, and enhanced throughput…

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802.11 PHY Compatibility – Basic Overview

802.11 PHY Compatibility – Basic Overview

802.11g <–> 802.11 / 802.11b: When 802.11g (ERP-OFDM) was released in 2003, we needed a way to co-exist with the large installed base of older 802.11 (DSSS) and 802.11b (HR-DSSS) based networks and equipment out there.  The solution to the problem used RTS/CTS control frames to silence the channel before an 802.11g station used any of the higher modulations.  Before transmitting a frame using OFDM modulation, the transmitting station would initiate an RTS / CTS exchange with the receiving station.  The RTS/CTS…

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What does 802.11 Contention Look Like (Part 3) – Probabilities & Our First Model

What does 802.11 Contention Look Like (Part 3) – Probabilities & Our First Model

In my previous blog posts in this series I covered the inherent problem with CSMA/CA and how it loses efficiency as more stations make use of a channel.  I also covered some of the basic rules of how CSMA/CA works as implemented by 802.11 Wireless LANs. As I mentioned at the beginning of this blog series, my intention here is to build an argument and the logic for describing what WLAN contention actually looks like in the real world.  We’ve…

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What Does 802.11 Contention Look Like (Part 2) – How contention works:

What Does 802.11 Contention Look Like (Part 2) – How contention works:

802.11 Medium Access Control implemented with the Distributed Co-ordination Function (DCF) and Enhanced DCF Channel Access (EDCA) methods, uses a random back-off counter to help ensure that clients do not transmit their data at the same time, but rather take turns to send their data one after the other.  This is the “Collision Avoidance” part of CSMA/CA. When two (or more) 802.11 stations both have data to send on the same channel and both have established that the channel is…

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What Does 802.11 Contention Look Like? (Part 1)

What Does 802.11 Contention Look Like? (Part 1)

The IEEE 802.11 Wireless LAN protocol uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with a fairly robust arbitration mechanism to allow WLAN Stations (STAs) to gain access to the wireless medium based on their traffic priority. The central problem with CSMA/CA and the 802.11 arbitration mechanisms is that the chances of a collision occurring between two stations increases seemingly exponentially with the number of active stations contending for the wireless medium.  This means that as more and more…

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Wi-Fi CSMA/CA – Going Deep

Wi-Fi CSMA/CA – Going Deep

In my career as a Wireless Engineer I have read a whole bunch of articles on Wireless Arbitration and how it works and to be perfectly honest, I have not ever really looked deep enough to fully understand how the carrier medium is actually marked as busy by the PHY and MAC layers. I learnt pretty early on that at the beginning of the transmission of a frame, there is a field somewhere that tells all the other stations to…

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