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wireles network hacks mods - briere D.

briere D. wireles network hacks mods - Wiley publishing, 2005. - 387 p.
ISBN: 0-7645-9583-0
Download (direct link): wirelesnetworkhacks.pdf
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Picking a Technology
For the most part, we’re pretty agnostic regarding how broadband services are delivered — as long as they are delivered. We wouldn’t care if someone ran a length of barbed wire to our homes, as long as it got us fast Internet access for our wireless networks. (We’ve actually seen DSL running over barbed wire, as a matter of fact!)
Having said that, there are some substantive differences between different Internet technologies — not only in how they are delivered, but also in what they deliver.
The following is a general guideline to what’s out there, and how these services typically differ from each other.
Don’t get too caught up in the generic differences between different technologies. It’s entirely possible that in your town, what we say for cable applies to DSL and vice versa!
Chapter 4: Wi-Fi and Broadband Connections
Wither DSL with 802.11?
As we’ve mentioned throughout this chapter so far, two primary technologies are used to provide broadband network services to homes — DSL and cable. DSL (or Digital Subscriber Line) is the telephone company’s main entry into the broadband world (although many are moving to fiber optic connections — see the sidebar titled “Fiber comes home” elsewhere in this chapter for more information).
DSL services use a common copper telephone line, combined with some very sophisticated “modems” using digital signal processing (DSP) devices that can cram a lot more data across a phone line than a conventional analog modem can. There actually isn’t a single “DSL” technology out there — there’s a huge range of DSL variants, each with its own specific characteristics.
These variants (or line codes) are named by simply adding a letter to the beginning of the letters DSL (replacing the x in xDSL). There are many forms of DSL (some defunct, some used for very specialized purposes that you’ll never see), including the following common variants:
ADSL: This is the most common variant of DSL. The “A” stands for asymmetric, which means that the upstream speed is significantly less than the downstream. ADSL is a relatively low-speed solution — maximum speeds reach 8 Mbps downstream, and real-world speeds are well below that — but because it can serve customers over existing telephone wiring up to three miles in length, ADSL is widely deployed throughout the world. ADSL was the first consumer version of DSL on the market.
ADSL2/2+/2++: These are the newest developments of ADSL, designed to increase both the speed and reach of the older ADSL technology. The equipment for ADSL2/2+/2++ has been developed, is in production, and is slowly being deployed by telephone companies. Under ideal conditions, it can provide speeds downstream of around 20 Mbps, and upstream speeds of a few megabits per second.
^ SDSL: Symmetric DSL offers equal speeds in both directions and is mainly used for business connections at speeds of up to 1.1 Mbps. The newest variants use a technology called G.shdsl to bump the speeds up over
2 Mbps.
^ VDSL and VDSL2: Very high-speed DSL! What a great name. Makes us happy! VDSL is indeed the fastest of the DSL variants and can provide downstream speeds as fast as 50 Mbps — but only at very short distances (a few thousand feet of phone line, at most). VDSL is most typically deployed in areas where fiber optic cables run to the neighborhood, but not directly to the home. VDSL2 is the almost (as we write) approved upgrade to VDSL, designed to provide higher speeds at longer distances. We can’t wait!
64 Part I: Making Your World Wireless
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Because the vast majority of DSL lines in place everywhere in the world but Japan and Korea are ADSL lines, we discuss that variant of DSL here:
Speed: Most DSL services offer downstream speeds between 1 and
3 Mbps, with higher speeds occasionally available for premium pricing. The downstream speed typically ranges from 128 Kbps to 1 Mbps. Most DSL services are slightly slower than similar cable services.
DSL speeds are highly distance-sensitive — the further away your home is from the local phone company office (or the outdoor “remote terminal” where your DSL circuit terminates), the slower your speed is, all other things being equal. The speed you get may not be the speed you think you bought!
Price: DSL is (in the U.S. and Canada at least) usually the most inexpensive broadband connection available. Telephone companies got off to a slightly slow start compared to their competitors at the cable companies and are trying to make up ground with lower prices and good bundling deals. You can get a basic DSL line from many telephone companies for about $35 a month, but the price can vary depending upon how long a contract term you agree to and how many other services you purchase from the phone company. This is about $10 a month less than most cable companies charge for their basic service (generally speaking, cable companies choose to offer more speed at a higher price).
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