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physical layer of wireless local area network


The physical layer is much more vulnerable in a wireless network because the physical medium used to transmit data is simply the air which is open for anyone to access. It is for this reason that wireless networks are significantly harder to secure. Since the physical layer is so much more susceptible to an attack, it is very important that link layer protection is sound. The link layer is responsible for controlling user authentication and data encryption. It is subdivided into two tiers – Logical Link Control (LLC) and Medium Access Control (MAC). With weak link layer protection, it becomes much easier for a hacker to break into the network and capture data. The research 802.11 standard provides guidelines regarding specifically how this link layer protection is to be implemented.

While research 802.11 has no physical layer in the sense of wires and cables, it does still transmit and receive data frames via the ether. It accomplishes this using different spectrum modulation techniques. Spread spectrum is a data transfer technique that attempts to reduce interference by using a much larger bandwidth than is really needed. The three different types used primarily in research 802.11 are Frequency Hopping Spread Spectrum (FHSS), Direct Sequence Spread Spectrum (DSSS), and Infrared (IR). Each one utilizes different data transfer speeds. Doing this reduces the peak power while keeping the overall power the same. The research 802.11 standard also specifies rules for the Medium Access Control layer. The most notable rule is Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA). This service is “a mechanism for sensing whether the medium is in use before transmitting” . If the medium is already transmitting data, the station wishing to send data will wait for a random amount of time and then attempt to re-transmit.





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