2alpha - Networking 101

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High Speed Networking 101

Computers that are close together get connected using LAN (Local Area Network) technologies. Ethernet is the most common example.

Computers (or more commonly, whole networks) that are far apart get connected using WAN (Wide Area Network) technologies. The phone system can be thought of as a Wide-Area network for people or computers using modems. It is both switched and intermittent since you can dial different numbers to connect to different places (switched) and you usually hang up when you've finished communicating (intermittent).

ISDN is a faster and less error-prone version of the same type of connection. You can also get what are called leased lines which are, in essence, pre-wired phone lines that go to a specific place without needing to be dialed. This is the preferred method of connecting a business to the Internet, since leased lines offer much higher speeds than any current switched service, and you're always connected. The ability to connect to different places isn't necessary, since the Internet itself allows you to connect to any other computer (or multiple computers) directly.

Leased lines are offered in 2 speeds appropriate to home or small business use - Digital Data Service (DDS or 56k) and T1.

DDS is a medium-speed technology that is relatively inexpensive. It uses what are essentially 2 phone lines, one for transmit and the other for receive, to move data at 56000 bits per second - about twice as fast as the fastest modems. Equipment for DDS is also significantly cheaper than equipment capable of handling higher speeds.
T1 is a high-speed technology originally used for telephone trunk lines carrying 24 conversations at once. It can also be used to carry 1,536,000 bits of data per second (more commonly referred to as 1,536 kilobits or 1.536 megabits). You can also order fractional T1 at 128k, 256k, and 384k (using 2, 4, or 6 voice channels, respectively) to save money on line charges, but the equipment is the same for all T1-level service.

To use a leased line you need a DSU (Data Service Unit - roughly equivalent to a modem, but for leased lines) and a router (basically a small computer that knows how to connect a LAN to a WAN). You will also need Ethernet cards for any computers that you want to connect to the network and possibly software as well. DSUs are specific to the type of line you are using - a fractional T1 DSU can run at 56k, but it still can't connect to a DDS circuit. Routers simply need to be fast enough to handle the speed of the connection. A router capable of handling a T1 line will happily run at 56k, whether that circuit is DDS or fractional T1.

Frame Relay 101

Traditional wide-area networking used leased lines to connect different locations directly to one another. This is fine if you only want to connect 2 places to one another, but you have to buy equipment for both ends of each line, so it gets expensive if you want to connect even a few places together. Frame Relay solves this problem using a technique called multiplexing. You install one set of wires and one set of equipment at each location which are then shared by all of the connections to that point. While a typical business these days has only one connection (to the Internet, which allows "virtual" connections to any other computers which are also connected to the Internet), their service provider would need to have a large number of connections (one to each customer, plus one or more to the other providers who collectively constitute the Internet "backbone"). Frame Relay greatly reduces the provider's costs, which makes it possible to reduce your costs. An extra benefit of Frame Relay is that the phone company charges are usually distance-insensitive, so you don't need to live near your provider to get low rates.