A Network Operations Center (NOC).
“Press 1 to speak to the only person on
duty at this time. Press 2 to leave a
brief message that will be ignored.”
Ah, the age-old question — at least since the Internet became a household fixture. At one time or another, all of us have complained about slow network speeds. You try to watch a YouTube video, but it’s agonizingly slow. Why?
Let me give you a slap-happy, as-non-technical-as-possible look at how this works and how you can (sometimes) improve things.
If you want the gory details, Wikipedia has them, starting with this article on OFDM (Orthogonal Frequency Division Multiplexing), which is the most commonly used method.
In various forms and flavors, OFDM (or something very much like it) is used in Wi-Fi, DSL, Digital TV, HD-Radio, DAB in Europe and a host of other applications.
Ergo, the first thing we’ll do is look at just how this works … and why it matters to your download speeds.
Typical spectrum for ADSL. “POTS” is
geek slang for “plain old telephone
service” (i.e., voice). The narrow
spikes are the subcarriers — the
“data buckets” (explained next).
The Data “Buckets”
Here’s the first quick and dirty. When sending a lot of data, a very common approach is to split that data into very small chunks and then to stack them onto separate subcarriers at different frequencies. (If you’re old skool like me, imagine connecting a bunch of old US Robotics modems to a bunch of AM transmitters, each on a different channel.)
You can picture this as a bunch of stacked “data buckets,” starting with low frequencies and moving up to higher and higher frequencies. Each bucket contains a chunk of data. The more “buckets” you have, the more data you can send or receive.
The old Bell Labs wrote the book and/or laid the groundwork for most of these techniques. They’ve been multiplexing and stacking signals for ages. In the old days, this usually required rooms filled with equipment. Nowadays, tiny little integrated circuits take care of everything, allowing a very sophisticated multiplex system to be crammed into a small Wi-Fi modem.
But again, the fundamental principle is this: your high-speed data is split into a bunch of chunks and stuffed into “data buckets.” These “buckets” are little narrow-band subcarriers at different frequencies. The chunks are pulled out of the “buckets,” decoded and reassembled at the receiving end.
Each “bucket” is at a different frequency,
higher frequencies are toward the top.
Reliability vs. Bandwidth
The biggest advantage to this approach is reliability … but this robustness comes at a cost. You are literally trading bandwidth for reliability. The link will do whatever it can to keep linkin’, but in many cases, it has no choice but to “slow down” if things are heading south.
The equipment will periodically reassess the link, checking the quality, determining which “buckets” are usable, and so on. If you have bad wiring (more on this in a moment), the link might work fine one minute, then be terrible the next.
If there’s interference or noise, the bandwidth will drop, because some of the “buckets” become unreliable. You might still get a connection, but it will slow down noticeably.
Here’s an example (speaking from personal experience): AM radio stations transmit between 530 and 1700 Kilohertz (KHz) — .53 to 1.7 Megahertz (MHz). That’s right in the middle of the ADSL bandwidth shown above. If you live near an AM transmitter, can you see why you might have problems?
In this (outstandingly artistic) image,
I’ve added interference and noise. Now
the top “bucket” is unusable. You’ve
lost 25% of your bandwidth in one go!
Ask any RF engineer (like yours truly): the higher the frequency, the more careful you have to be. All wiring runs should be as short as possible. When you’re making your work neat, don’t make sharp bends and don’t tie the cables together too tightly. You’ll smish the wires inside, which can cause “crosstalk” (the signal on one pair of wires interferes with the pair beside it). Use smooth curves around corners. To store excess wire, loosely roll it into a loop.
The paired wires inside the cables are twisted; this is important, too. (Click here to read about balanced lines if you want the gory details.) If you’re putting your own RJ11 or RJ45 plugs onto the cable, keep the pairs twisted as closely as possible into the connector. If you “untwist” the wires, you’re more susceptible to interference.
For classic DSL on copper phone lines, a DSL filter is required. On the newest boxes, this may be built in (my ATT “U-Verse” box is self-contained). Otherwise, you’ll need a good DSL filter to keep the voice and data separate. If you’ve had a lightning storm recently, and your data speeds have dropped, the first thing to check is your DSL filter, if you have one.
Super tip: find your telephone interface. This is typically a little plastic box outside of your home. Most of the newer ones will have a little RJ11 or RJ45 jack inside. Unplug the lines into your house and plug the DSL modem directly into the interface. If your Internet starts working, you’ve either got a bad DSL filter, or your house wiring is bad.
A typical DSL filter. The incoming line is
split into DSL and phone (voice) outputs.
You’ve probably seen or heard, “DSL is only good for a mile or so.” That actually varies greatly depending on the quality of the copper wiring (and some of it really, really bad).
In many cases nowadays, the telco actually runs fiber (or some other high-speed link) to your neighborhood. This high-speed signal goes into a special box (for DSL, called a DSLAM — a Digital Subscriber Line Access Multiplier) that “breaks out” the Internet stuff, then does the “sliced-data and stacked bucket” thing on the copper wire into your home.
If you have classic DSL and if you’re located some distance from the DSLAM, you’ll probably have lower speeds. The higher frequency “buckets” will become unusable over that distance. Look at that ADSL diagram yet again: can you see why your upload speed might seem OK, but your download might be bad? The “downstream buckets” are at the higher frequencies.
Again: the test mentioned above is the best one. If you can plug your modem directly into the outside telephone interface and get good Internet, the problem is on your side of the wiring. If you can’t get Internet at the telephone box, call your telephone company. (Or you are just too far away, and there’s not much the phone company can do. Sorry.)
Figured I’d better show you this again. I’ve
referred to it several times now, after all.
This “stacked bucket” approach is also used in most wireless links — from the high-tech microwave systems that my company uses to the Wi-Fi router in your bedroom. The data is split into little pieces and then stacked into “buckets” for delivery, one atop the other, at different subcarrier frequencies.
Same as with wired DSL, if you’re getting a weak signal, or if there’s interference, your link speed plummets. It might still work, but so many “buckets” have been compromised, there aren’t many left to carry good data.
Obviously, the biggest trick with Wi-Fi is to make sure the signal at your device is as strong as possible. Move the Wi-Fi box closer to you. Remember that it won’t punch through solid walls very well. If you’re trying to get your mobile carrier’s wireless, sit near a window.
Also, using the Wi-Fi router’s Web interface, try different channels. This is becoming a real problem in crowded neighborhoods: a bunch of people are on the same frequencies.
One of my wireless links: an 8′ dish mounted on an old
AT&T Long Lines tower near Warrior, AL. We use
fiber to get the signals into and out of the dishes.
There’s another thing to remember: the Internet itself can become busy at times. Maybe the Website that you want to use is just temporarily overloaded. That’ll be obvious, because the one you want isn’t responding well, but you can go to a different site and it’ll be fine.
I almost got into an argument with an AT&T technician over this next one (he was wrong, I was right); only the realization that arguing on the Internet is a waste of time prevented me.
I mentioned above that the telcos routinely send data into your neighborhood over a fiber or other high speed link, then split it out for different customers. No link has infinite speed. If your neighborhood is filled with people who all want to download movies at the same time, your Internet speeds will suffer because the local distribution point is temporarily overloaded.
(The fact that the AT&T guy denied this didn’t improve my already-low confidence in the abilities of the average AT&T technician, by the way.)
When this happens, all you can do is wait it out.
Satellite Internet services are available, but frankly, we’ve had spotty experience with them. See above re: lots of people trying to use something at the same time; it’s really bad with satellite Internet service. If you just can’t get reliable Internet at your home, though, maybe it’s an option for you.
One Final Idea …
If a neighbor up the road has good Internet, offer to split the cost with him/her. If it’s too far to run a weatherproof cable, try an unlicensed wireless link to get it into your house. These are surprisingly inexpensive now (see the picture below); Google “ubiquiti” for a company that we’ve used. The self-contained dishes are around $100-200 each. Obviously, you’ll need two of them.
The only drawback is that these wireless links are line of sight only. They won’t punch through trees, hills or thick walls. Mount them as high as you can on a chimney or rooftop. The unlicensed ones also use the same frequencies as Wi-Fi, so you may have to juggle channels to get a good signal.
Final, bold-print disclaimer: I vastly oversimplified my description(s) above. I also made the terms “speed” and “bandwidth” equivalent, which isn’t accurate (even though I’m certainly not the only one who does it.) (Heh.)
I didn’t even get into (for example) data collisions (i.e., two devices try to access the same network at the same instant) and other things that can cause problems. I didn’t cover error correction and a bunch of other stuff.
But hopefully, this little ditty will give you a decent start.
Ubiquity wireless links. Cheap and good!
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