B O T T O M L I N E
The path to Internet connectivity can sometimes be a slippery slope. Here are five things to watch out for when choosing your ISP.by Joel Snyder
Internet service salespeople seem to think that all prospective customers are rosy-cheeked hicks more in tune with turnips than terabytes. It's amazing the kinds of myths you'll hear when the salesperson thinks you don't know anything about Internet connectivity. If you're thinking of buying a high-speed connection from an Internet service provider (ISP), you're probably going to run into one or more of these myths and half-truths.
Getting WiredMyth 1: Fiber is better than copper. Not really. Bits travel just as well over fiber, copper, or radio waves. Yet many ISPs trot out their fiber-optic cables as if they were a badge of honor, implying that those old-fashioned copper-based ISPs are dinosaurs.
Local ISPs usually talk about fiber when describing the connection they have to their (national) ISP or, in the case of the really big boys, the connection they have to the Internet's network access points (NAPs), where the biggest ISPs exchange data traffic. Since most local ISPs buy service from bigger ISPs above them, the speed of your connection to the bigger ISP is crucial to total performance. The biggest, fastest, and best- connected of the ISPs (MCI, SprintLink, BBN, etc.) are called network service providers or "tier 1" ISPs. Folks who connect to them are "tier 2" ISPs and so on down the ladder.
Despite what some ISPs might say, copper and fiber are a lot alike. Both copper and fiber can be wired redundantly so that a single cable cut doesn't take down the line. The only time you really need to have fiber is when you want a single circuit at speeds of 45 Mbps, usually called a T-3, or higher. Most ISPs that claim to have a T-3 are bending the truth; very few really need to have fiber (more about this in Myth 2). Nevertheless, fiber sounds cooler and faster and better, so everyone wants it.
In some cases, an "all-fiber digital connection" is not preferable to copper. One nice thing about copper is that you need lots of copper lines to build high-speed access. If any one copper line goes down, the service is diminished by only a small fraction. With fiber, all your data travels over a single fiber channel, so there are many potential points of failure that can bring your ISP down completely. Look for an ISP with multiple connections to multiple tier-1 ISPs, and don't worry whether it's using fiber or copper.
There are some other minor myths, half-truths, and misleading information revolving around the fiber frenzy. For example, one company I spoke with swore that its "error-free digital fiber T-1" would give better service than a competitor's noisy old analog T-1. That's nonsense. Error rates in any digital circuit, fiber, or copper are so low as to be insignificant. In any case, the built-in error checking in TCP/IP hides any errors that pop up.
Changing ChannelsMyth 2: All T-3s are created equal. Technically, this is true. But it's not the T-3 itself--it's how the ISP uses the T-3 that matters. T-3 is an old telephony term that has been revised in the ISP world to mean any circuit running at about 45 Mbps. It's sloppy to refer to a piece of a fiber circuit as a T-3, but the meaning is generally understood by the industry.
When an ISP uses a T-3, it is unusual to see a solid 45-Mbps pipe transmitting data between point A and point B. Usually, the ISP has the telephone company turn on only a segment of the available bandwidth. The telco charges for each channel you turn on, so most ISPs start with only a few channels, keeping the others in reserve. Of course, most salespeople gloss over this point. To hear them talk, every T-3 is a full, direct pipe running at maximum speed.
Because a T-3 is raw bandwidth, how it's utilized by the ISP is crucial to how much data you can push through it. For example, a point-to-point connection with a full T-3 gives you the best possible throughput and response time. But it's much more common for an ISP to use only a part of a T-3 to connect into an asynchronous transfer mode (ATM) network, which then routes the data to a higher-level ISP. ATM is fast, but it's not as fast as a point- to-point connection. Also, ATM has an overhead called a "cell tax," and, depending on how the network is engineered, you can lose as much as 30 percent of your bandwidth to this tax.
Hops, Latency, and LossMyth 3: Hop count matters. Wrong! Hop count is irrelevant. (A hop is one of a series of transmissions to move a file from point A to point B.) ISPs like to brag about the small number of hops they are from this or that NAP. But what really matters are latency and loss: how long it takes your bits (electronic packets) to get from your computer to their destination, and how many of those packets get thrown in the trash can along the way.
Hop count measures the number of switching stations your packets pass through on the way between source and destination. In principle, the more hops, the worse the service. In fact, some hops are fast and some are slow. You can see these hops yourself from your own computer using traceroute, which is available on all popular platforms. Or, if you can't figure out how to run traceroute on your PC, point your browser to the Web page I put up specifically for this column at http://www.opus1.com/www/traceroute.html and see what it looks like from my computer.
At one time, the NAPs were the place to be. If your ISP could get your packets to the NAP in a hurry, you were in great shape. Then the tier-1 ISPs--those that connect directly to the NAPs--started bringing in 45-Mbps and 155-Mbps lines and, wonder of wonders, the NAPs began to resemble downtown Manhattan during rush hour. They still do, and they're not going to get better any time soon.
The NAPs are the last place you want your packets to pass through, and counting hops to the NAPs just tells you how soon your packets will get clogged in the NAP traffic jam. If you want good performance, look for private interconnects, sometimes called "peering arrangements," between providers. They offer a less-congested and higher-speed path between two big networks. In the end, it's not a question of who has the most connections to the NAPs; it's who has the best connections to other ISPs.
Duplex DuplicityMyth 4: Full duplex is the same as half duplex. This is one of those myths of omission. A telecommunications line is either full duplex or half duplex. On a full-duplex line, like a T-1 or a T-3, both sides can talk at the same time. On a half-duplex line, like Ethernet, only one side of the line can be talking--the other has to be listening.
Many companies are now selling Ethernet connections, which they call 10-Mbps lines. That's a misleading appellation. Ethernet is half-duplex. If you want to call an Ethernet line a "10 Mbps" line, you have to call a T-1 line a 3-Mbps line. But no one does that because everyone knows that a T-1 line is 1.5 Mbps.
An Ethernet line is, in reality, 5 Mbps, with burstable 10 Mbps. That means that if you only send or receive data, you'll see bursts of around 9 Mbps. Like ATM, Ethernet has a substantial overhead that keeps it from reaching a full 10 Mbps, even when bursting. But if you send and receive data at the same time, you'll see a long-term throughput of about 5 Mbps per side.
If you simply want to host a Web site, Ethernet is both adequate and affordable. But if you want to provide connectivity to a big company that will receive as much data as it will send, two or three T-1 lines will give you much the same result as a "10 Mbps" Ethernet line.
Don't Ask, Don't TellMyth 5: Engineering, load factors, and disaster recovery are secrets of ISPs. If your Internet connection is essential to your business, you deserve to know how your ISP builds, maintains, and expands its network.
Any ISP that refuses to give out information about its operation is either hiding something, or, worse, too embarrassed to admit that it doesn't know the answers to your questions. These myths aren't the only things you need to know about buying a high-speed Internet connection for your business. There are a lot of questions you should ask before signing up with anyone. Don't let the glib technobabble of an overactive sales person confuse you into buying the wrong service.
Joel Snyder is a senior partner at Opus One in Tucson, Ariz.
Reprinted from Internet World magazine Vol. 8 No. 5 (c) 1997 Mecklermedia Corporation. All rights reserved.