transmission

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Cabling
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Routers
Switches
Why don't we transmit digital data over the telephone line directly?

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It’s all a matter of bandwidth (not to be confused with throughput). All digital communications is a combination of a very low voltage typically known as a binary zero and a fixed higher voltage known as one that switch back and forth. Digital is actually a very defined analog signal. The surrounding environment (circuit board, connector or cable) has to be designed to handle a certain amount of bandwidth to reliabily handle digital communications. ANSWER: The phone line is designed only to handle a small frequency bandwidth such as the voice range (300 to 3000 hz). OPTIONAL: Over time we developed methods of how modify the digital signal so it could modulate at a high rate as well as modulate within the gaps of the modulation and invoke phase shifting at the same time with the end result of effectivally carrying the data of the digital communications at real time but as analog within a 300 to 3000 hz range. I hope I didn’t go to far. This was a tough questions and involves a lot of physics and an understanding of data commuications.

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  • Bobkberg
    Since HatcherBob covered the physical portion beautifully, I'll take a different whack at it. We've got millions and millions of phones out there, as well as older switching equipment that doesn't handle digital - especially in rural areas where just getting the line out there is a large part of the effort, economically speaking. The FCC has also ruled that you can't just upgrade the nature of the service and force people to spend money to adapt to it. Witness the long delay and battle over High Definition TV for a case in point. The broadcasters could have changed over years ago - but since television is a public medium, you can't effectively block out those who can't afford to buy a solution to the problem. Bob
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  • Yipych
    Also, can we connect 2 computers directly by using twisted pair. (Do not go through any ISPs) So, the problem of limited bandwidth will be eliminated.
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  • Bobkberg
    Yes, you can connect them directly. The only questions regard distance, and speed and reliability concerns. If they're within a single building - no sweat (technically speaking - since I don't know your building) If there is available fiber connecting multiple buildings. If farther, is there line of sight without trees or buildings in the way - then laser is the way to go. If farther - like a mile or more, then microwave is workable - again as long as trees, clouds, fog or rain are not a concern - since water absorbs microwaves very well (hence why microwave ovens work so well). If you can provide more particulars, then we (as an informal group) will be in a better position to advise you. Bob
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  • Yipych
    As you have mentioned, it is possible to connect 2 PCs by using twisted pair. However, in the real world, why there are no people using such method even if they are in the same house? Besides, is it the problem of distance that make us need to change the signal from digital to analog in order to transfer data over a long distance?
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  • Bobkberg
    If you're talking in the same house, there are several solutions. But first to answer your "why not". If you want to be neat about it - most people do NOT like wires all over the place. The wiring alternative is to poke holes in the walls and crawl around under the house, or up in the attic (if there are such spaces), and not damage the house/dwelling in the process. This is difficult, dirty and time consuming - plus most people don't have the skill to do a really good job of it, and they're not williing to pay a professional the $$$ to get it nicely done. There are alternatives though. Some products (don't ask me which ones though) use the power lines in the house with special adapters, others use the phone lines (which are not even Cat 2 or Cat 3 - let alone Cat 5 or 6), and there might be some which use the cable TV wiring - although I don't know of any. These are the reasons that wireless is so popular. One of my customers (family) has one old tower as a print server, and 5 wireless laptops - one for each family member. Personally, I'm one of those people who has installed conduit to every room in the house, and who will rip open walls and crawl through the attic to put the conduit where I want it. After all - If I'm going to crawl through the attic, why not install conduit (flexible) instead of just wire. It's a little more work - but I only have to do it once!!! Hope that helps, Bob
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