Wireless Standard question

ChrisRice

Okay so I'm reading the CompTIA Network + Review guide from Sybex and I'm onto 802.11. It mentions that 802.11a uses Orthogonal Frequency-Division Multiplexing, while b, g and n use Direct-Sequence Spread Spectrum (DSSS). In simple-ish terms, what does this mean?

I realise it's not part of the exam, but I'm just curious to know as 802.11a is faster than b and as fast as g, uses the emptier of the two frequencies yet isn't widely used. Why is this?

MrRyte

ChrisRice wrote: »

I realise it's not part of the exam, but I'm just curious to know as 802.11a is faster than b and as fast as g, uses the emptier of the two frequencies yet isn't widely used. Why is this?

IIRC; the problem is that 802.11a has a shorter range and can't penetrate walls or other obstructions as well and 802.11b/g.

it_consultant

As for the real difference between the two modes - who knows, except to say that G/N is clearly better than A/B. I was reading something about "protected mode" in G/N devices and somehow that is tied to DSSS.

Direct-sequence spread spectrum - Wikipedia, the free encyclopedia

ChrisRice

Ah okay, thanks.. Well I've read through that and through a few of the linked pages, and it sort of makes sense, but a lot of it went right over my head

JDH51086

The primary reason that 802.11a has a shorter range and poorer penetration capabilities is because it uses the higher frequency 5Ghz-range frequencies whereas B/G uses 2.4Ghz. As a general rule of thumb, lower frequencies penetrate materials better due to them having a longer wavelength, but lower data rates. You can pack more data into a wave that pulses 5.8 billion times per second as opposed to one that only pulses 2.4 billion times per second. N gets around that lower data limitation by using multiple data streams simultaneously.

If you get more interested in this stuff, take a look at the CWNA certification and training materials.