Wednesday, February 7, 2018

Chapter 2 - 802.11 Communications

This portion of the chapter discusses the methods/processes/procedures of finding and associating to an AP.  The 802.11 MAC layer has a number of mechanisms in order to do this, as well as to help traffic along.

Scanning - STA's are not just magically associated with an AP. They need to be able to find them first. Scanning is the methodology used to find BSS's. There are two types of Scanning, Passive and Active. These will be gone into further detail later

Synchronization -  There are certain features that may require the STA's to all reflect the same time. Beacon frames can provide a time stamp value for STA's to update their clock with

Frame Transmission - Nowadays this is DCF (Distributed Coordination Function)

Authentication - This takes place before the Association… its um, where the STA authenticates.

Association - The next step after a STA is Authenticated is becoming associated with the BSS. This process is much more akin to becoming associated with someone/something. The STA and AP find out various capabilities of each other. What they support, what they don't, etc. Much like getting to know someone.

Reassociation - We use wireless so we aren't tied to a specific location. As such, we often need to roam from one AP to another within the same ESS. To roam to the new AP, the STA must "reassociate" with it.

Data Protection - Since wireless uses plain ol' RF, it can be "listened to" by those who may be inclined to do so. Data Protection allows us to use encryption techniques to try and thwart potential attackers.

Power Management - Most, if not all STA's utilize battery power. Which, as anyone who uses a Smart Phone can attest, is a valuable commodity. With this in mind, Power Management features have been created to help optimize the battery life of these devices. They do so by allowing devices to go to "sleep" for certain periods of time. Therefore they don't "pull" any extra power.

Fragmentation - The wireless medium can have a number of influencers on its stability. Due to this, it may be prudent to fragment frames before they are sent. This will be covered more deeply later on.

RTS/CTS - Request to Send and Clear to Send are basic functionalities of the 802.11 standard. These help prevent (but are not 100%) hidden node issues. This too will be covered more deeply later on. 

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