|
| home |
Andre's Quick Tutorial/Reference Guide to Internet Connections.
Most of the things you can do on the Internet involve transferring files from some remote computer to your own computer. Whether it be viewing a web page, which usually consists of several files (each image on a web page is a separate file, and also the text portions of a web page are contained in a file), or downloading a game from a ftp server, the basic action is to get the file from point A to point B. When most people think about taking files from one place to another, they think of floppy disks. Certainly, that is a valid way to accomplish this task, but it's also a bit impractical since you have to physically transport the disk itself. That's not a problem if you have two computers sitting next to each other, but what about if you want to get a file from a computer far away? That's where the Internet comes in. Instead of using floppy disks as the medium for transferring files, we instead use digital communications lines that are strung throughout the world. It's like the telephone system, but instead of voices, the lines carry digital computer data, and instead of using old-fashioned "analog" phone lines, the Internet utilizes higher speed digital communications circuits. By connecting your computer to the Internet, you instantly have access to the vast resources contained on other computers all over the planet that are also connected to the Internet.
However, all Internet connections are not created equally. Some are fast, allowing the user to very quickly leach data from the net, and others are painfully slow. It's important to note that the only real difference is speed - you have access to the exact same stuff regardless of how you connect to the Internet. Speed is a big - perhaps the biggest - factor when it comes to Internet access. It's pretty easy to understand that the faster your connection is, the less time you'll spend waiting to get whatever it is you want out of the Internet. The most common - and the slowest - kind of Internet connection uses modems and telephone lines. Basically your computer dials into an Internet Service Provider, and the ISP acts as an intermediary between your computer and the Internet, allowing two-way communication between your computer and any computer on the Internet. If you're lucky, you have a cable modem, which allows for *much* greater throughput than a standard analog modem. Instead of using the telephone network to connect you to the ISP, the cable modem talks to the ISP (which is usually your cable company) over the broadband cable network that already exists - the same network that carries your television channels.
Anyhow, regardless of your type of Internet connection, you can find out if you're getting the performance you should. Since the primary goal is to move the most amount of data in the least amount of time, we evaluate the efficiency of an Internet connection by how much data it can transfer in a given time. You already know how to measure time - seconds, minutes, etc. The amount of data in a given file is expressed using bits or bytes. It's not really important to dig too deep here - all you need to know is how to find out how big a file is, which is important information if you want to find out how long it will take you to download this file. More on that later. Strangely enough however, while Internet connection speeds (and modem speeds) are usually measured in some multiple of "bits" per second (such as kilobits or megabits), computer file sizes are generally measured using "bytes" as the fundamental unit (don't ask me why, because I have no idea). This means that to obtain any sort of practical idea of how fast a given connection will move a file from one computer to another (which is, after all, what you use your Internet connection for), you'll need to do a little math in order to convert bits to bytes....the only thing you should remember is that there are 8 bits in one byte; anything else you need to know you can figure out. It is often helpful to express connection speeds in bytes per second; so for example with a 56K modem, the following would apply:
For those of you who weren't paying attention in math, here's the breakdown of that conversion. 56 kilobits per second is expressed as 56 kilobits over seconds. Since we need to convert to bytes, we multiply by 1 byte over 8 bits, which doesn't change the value of the expression, just the units. Bits cancel out, and after dividing 56 by 8, we're left with 7 kilobytes per second (note how the "kilo" prefix acts as it's own independent entity, separate from bits). This probably seems a bit over complicated, and it is until you've been through Chemistry where you have to do half a billion conversions like this. If that's too much to remember, then remember this: to change kilobits/second to kilobytes/second, just divide by 8. What that basically means is that with a 56K modem you could theoretically transfer a 7 kilobyte file in one second, or a 14K file in two seconds....you get the idea. Of course, since 56K modems (remember: 56 kilobit, not 56 kilobyte!) don't really go that fast in the real world (read the fine print on the box of your "blazingly fast" 56K modem and you'll see that FCC regulations limit you to about 52K or so - if you're a lawyer and would like to make some serious cash on all of this false advertising, drop me a line :-), you won't realize those speeds outside of a cleanroom anyway (this is due in part to cruddy old phone lines that were never designed for what they're being used for). Note also that Kbps stands for kilobits per second, while KBps stands for kiloBYTES per second (that also applies to Mbps and MBps). Not many people write them that way (as they should), but now you know anyway. I suppose I should also include a bit about prefixes for those of you who are new to this:
|
Prefix |
Multiply by |
| Kilo | 1,000 |
| Mega | 1,000,000 |
| Giga | 1,000,000,000 |
| Tera | 1,000,000,000,000 |
So, one megabyte is equal to one million bytes. Now that you've read this, I can tell you that you don't need to know that, because nobody ever expresses anything in bytes. The same is true of connection speeds, which, again, usually use bits as the basic unit - most of the time, speeds are expressed in kilobits per second (a 33.6K modem means 33.6 Kilobits per second). For example, you might hear someone say "Ya, man, the Internet was WAY fast last night...I was getting like a hundred K a second!". This lucky fellow probably has a T-1 or perhaps a cable modem as his link to the Internet, both of which are quite desirable. Someone with a cable modem could realistically download in one minute something that would take someone with even the fastest analog modem fifteen minutes. I personally have experienced sustained speeds of about 150 Kilobytes/second downloading from the netscape ftp servers with a cable modem. Even at 100 Kilobytes/s, that's still 6 megabytes of data EVERY MINUTE, which is almost enough to make a modem-using warez trader wet himself. If you were to express that in kilobits/second for the purpose of comparing it to a regular modem, it would be somewhere in the neighborhood of 800 - 1200 kilobits per second. 1200 is a lot bigger than 56. I'll pay an extra $20 bucks a month for that. (of course, if we were to mention the *maximum* possible speed of the cable modem, as most companies do with regular modems, we'd be sitting at a hefty 10,000 kilobits per second, or 1.25 MEGABYTES per second).
Please remember the difference between bits and bytes! It's amazing that many people don't really understand the units upon which these expressions are based (after reading this, you do). Find the nearest computer blowhard who loves to brag about his cable modem and how fast it is and then ask him "So, are you getting a hundred kilobits per second or a hundred kilobytes per second?". If he doesn't know the difference, he'll quickly make something up. If he's smart, though, he knows that a hundred kilobits per second is nothing to brag about. The only way you'll have any idea how fast you're going is if one of your programs tells you. For example, when downloading files with a browser, somewhere it'll tell you the rate at which the file is downloading. Browsers display speeds kilobytes per second (or, if you're really fast, megabytes per second) to express speeds, so you needn't do any of the aforementioned math, unless you want to know how fast you're going relative to the maximum speed of your connection, which is probably measured in kilobits/second. You can also get little programs that monitor your Internet connection and report to you how much bandwidth you're using at any given time. Give it a shot...it's fun :-).
Below is just such a screenshot I took from a program called IP Netmonitor. It's a very useful utility for a variety of tasks; one of the things it can do is monitor the amount of data going in and out of your computer. That's what this graph is showing. When you run it, it'll update every second, and the graph scrolls to the left as new data comes in. It's really cool to watch how file downloads usually come in spurts (at least on my network). This was taken from my desktop computer at work, which is a PowerMac 5400. It is connected via 10 BaseT Ethernet to a LAN which is in turn connected to a WAN with 1.54 Mbps frame relay. The server I'm downloading from in this case is on the other side of that frame relay link. Considering that the maximum possible bandwidth of a T-1 speed line equates to about 192 KB/second, my average of 118 KB/second (more than 16 times the speed of the fastest modem) is roughly 61% of the link's capacity. This is especially fun considering that Internet data going both to and from my entire district also pass over this line :-).
Which brings me to one last final point: the speed at which you connect to your Internet Service Provider is not always the speed you will realize when downloading files. This is true because you'll only realize (at best) the speed of the *slowest link* between you and the computer that holds the file you're downloading (regardless of what kind of file or server is in question). For example, let's say I have a cable modem that technically maxes out at 10 megabits per second (the top speed of the ethernet card in your computer where you plug the cable modem in). I have heard people say that the cable infrastructure is capable of supporting those speeds internally (but I'm not sure if I believe it). However, that broadband cable network in your town has to be connected to the Internet, and most of the time your average ISP doesn't go above maybe a T-3 or two as their Internet connection. So, even though the ISP to Internet connection may be faster than 10 Mbit/s, you won't get anywhere NEAR that fast when downloading. In this case, you obviously are not a slow link; but what about the server that holds the file you're downloading? If that server is attached to the net via a T-1, then you'll be limited to that speed (1.54 Mbps). If I had a regular old modem, however, I could rest assured that I would be the slowest link between myself and the target file (unless you're trying to hit a website that's being served at someone's house over their modem, which is not recommended if you want to retain your youth - most Internet servers are connected to the Internet with high-speed lines). Since connections within the Internet are always really quite a bit faster than any modem, you can usually pretty much max out your analog modem any old time of the day by downloading from any old site.
I lied. I have one more final point. You also won't always realize the full speed of your connection (whether it be a 28.8 modem, T-1 or cable) for the same reason that you can't drive 80 mph through downtown. Sure, your car might be able to go that fast (or if you're me, almost that fast), but there's one small problem: traffic. When other people get online (and they always are), they are competing for bandwidth with other Internet users. So, for example, if I have a T-1 and I'm hitting a website that's served off a T-1, I won't realize full T-1 speeds because maybe there are ten other people hitting that same site at the same time. If that's the case, the Gods of the Ether divvy up the available bandwidth as they see fit :-). Actually, it's sorta based on the connection speeds of the people who are requesting the bandwidth in the first place; obviously Joe F. Schmoe on his phunky 14.4 modem will get less bandwidth than me on my T-1 if we both hit the same server at the same time. It also seems to be related to what kind of protocol you're using; for example, if you're doing real-time type stuff like watching some QuickTime TV, that's a situation in which you need a constant stream of data flowing in your direction, otherwise you get an unwanted simulation of musical chairs as your data stream gets broken up to make way for other people's traffic. Ideally, the Internet is smart enough to know that the media you're consuming is real-time, and therefore will give your data stream preference over somebody hitting a web page, which is not as time-sensitive as what you're doing. They'll still get the web page, but a little slower than if you weren't listening to All Things Considered, or some other fine NPR program.
It's not always as clear-cut as that, though. Oftentimes driving around on Saturday morning in Bradenton, FL during tourist season (does that mean we can legally kill them??), you'll ask yourself "Where the hell are all these people GOING!". You can't tell; all you know is that there are tons of people on the road (judging by their speed, I can only assume that the driving itself is part of the attraction, to be prolonged and savored). The main intersections are usually the ones most backed up, simply because lots of people need to go through them to get wherever it is they're going. The exact same thing happens on the Internet (except of course you don't run the risk of being disfigured by some cataract-ridden snowbird). There are big Internet intersections (otherwise known as exchange points or peering points) where bottlenecks can occur. For the same reason that I love driving home at 4 a.m., I like surfing the net during non-peak hours (mornings, weekends).
Okay, I think that's just about everything you need to know. Here are the charts I promised you:
Traditional user to ISP (Internet Service Provider) Connections:
These are the kinds of connections that are widely available to the average consumer. The first four require only a single phone line and of course a modem; the last three need special lines installed by the phone company, and either an ISDN 'modem', or routing equipment. By the way, don't buy ISDN - it's a horrible value. If at all possible, get a cable modem (read on).
| 14.4 Modem | 14.4 Kbit/s |
| 28.8 Modem | 28.8 Kbit/s |
| 33.6 Modem | 33.6 Kbit/s |
| 56k Modem | 56 Kbit/s |
| Leased Line (56K) | 56 Kbit/s |
| Single Channel ISDN | 64 Kbit/s |
| Dual Channel ISDN | 128 Kbit/s |
High Speed Internet Connections
These are the kinds of connections that are available only in some areas, and at higher prices. ADSL is even now being tested and deployed in select cities in the US. The same is true of the cable modem, which is *by far* the best value around. Cable companies all around the nation are beginning to offer Internet access via cable modem technology. As more and more people get them, there will be a larger demand for them. Behold as the bar for bandwidth explodes upward over the next few years. You'll pay about $35 - $45 a month for unlimited use, and it performs at least as well as a T-1, which would probably cost you around a grand a month, counting telco charges and ISP charges. The other great thing about cable is that the phone company doesn't even get involved (at least, not at your level), and also that the cable company IS your ISP. (some cable companies can only deliver data TO your computer over their cable network, and require you to use a regular modem in tandem with your cable modem for "upstream" data - i.e. requesting files, telling the Internet which website you want to go to, etc.)
DSL speeds are for links < 12,000 ft. from central office
| Frame Relay | 64 Kbit/s - 1.544 Mbit/s |
| T-1 | 1.544 Mbit/s |
| Asymmetric DSL (ADSL) |
6 Mbit/s Downstream
640 Kbit/s Upstream |
| Consumer DSL (CDSL) |
1 Mbit/s Downstream
128 Kbit/s Upstream |
| High-speed DSL (HDSL) | 1.544 Mbit/s |
| ISDN DSL (ISDL) | 128 Kbit/s |
| Rate-adaptive DSL (RADSL) |
6 Mbit/s Downstream
640 Kbit/s Upstream |
| Single-pair HDSL (S-HDSL) | 768 Kbit/s |
| Symmetric DSL (SDSL) | 2 Mbit/s |
| Very high-speed DSL (VDSL) |
51 Mbit/s Downstream
2.3 Mbit/s Upstream |
| Direct PC (satellite) | 400 Kbit/s |
| Cable Modem | 10 Mbit/s |
Internet Backbone Connections
These are used to connect ISPs to the rest of the Internet, or to connect large organizations or "online entities" to the net. The bigger ones are used to connect different exchange points on the Internet together. You don't really need to know this stuff here. Actually, the only reason I have this here is for those rare IRC sessions when people start talking about their wish lists, and you want to be able to mention somthing faster as your dream connection :-). The biggest trunk that's commonly in use is OC12, which is quite fast indeed. According to my sources, OC768 is theoretical only. The most common of these are the T-1 and T-3; my office has a T-1 which serves Internet access to quite a few different locations throughout our enterprise (we have a county-wide WAN), and my ISP has a T-3 Internet backbone. Corporations with a vested interest in providing Internet content to lots of people like Apple or Netscape also have very fast connections. Last time I checked, Apple was using two T-3s and an OC3 as their Internet conduit.
OC rates are for Packet Over Sonet. OC# is # times faster than OC1.
| Connection Method | Mbps |
| T1/DS1 | 1.54 |
| T3/DS3 | 45 |
| OC1 | 52 |
| OC3 (STM1) | 156 |
| OC12 (STM4) | 622 |
| OC48 | 2,488 |
| OC192 | 9,953 |
| OC768 | 39,813 |
| ATM | 155 Mbit/s, 622 Mbit/s |
LAN Network Connections:
LAN stands for Local Area Network, and refers to the kinds of connections within a single building. Ethernet is the standard here, and it comes in several different flavors, the most common of which are 10 Base-T and 100 Base-T. Most new computers now include ethernet cards.
| Connection Method | Mbps |
| 10 Base-T | 10 |
| 100 Base-T (fast ethernet) | 100 |
| FDDI | 100 |
| 1000 Base-T | 1000 |
All of this information is correct to the best of my knowledge. If you've found a mistake or discrepency, please drop me a line at dre@mac.com. Also, please ask any questions you might have. I don't pretend to be an all-knowing type, but if I do know I'll help out as best I can. This info was gathered on 11/27/98.