Glossary

Note: these aren't the definitions you'd find in a book. If that's what you want, then go look in a book. These are they way I would explain the terms to someone. I'd appreciate it if you'd let me know of anything that's misleading or just plain wrong, but I'm not trying to be too strict. Life is tough enough. Sometimes, I may show some sarcasm, though.

Firewall

A way to block unwanted traffic from a company's internal network. It can be as simple as a router that simply prohibits TCP/IP packets of a certain type from crossing the boundary between the company's LAN and the Internet. In a complex system, it will allow traffic only from certain IP addresses, or only certain kinds of traffic, or only traffic that has been authenticated somehow.

Hub

A hub is a little box about the size of a modem that you can interconnect a bunch of 10baseT ethernet lines with. A 10baseT line runs from each computer to the hub; the hub makes sure all the lines get all the traffic. See Routers and Hubs for more info.

ISDN

Integrated Services Digital Network. It was a great idea; it was very successful in Europe; but in the US of A, the telco's resisted until it flopped.

The idea was to replace the analog link between your house and the local telco with a digital one. The digital link could carry multiple voice lines, digital data, control signals, and all kinds of stuff over the same pair of wires usually used for a single voice line. It required the telco to put in a special card at their end of your line. At your end, there needed to be a network interface and then you could connect a variety of things to the other side of the interface.

In practice, ISDN prices and install charges were held high and lead times were kept long, so that few people installed it. It is really not a good choice now unless you can't get DSL or you need a reliable, moderate bandwidth connection between two points, like your home and your office, and you can't get it with a regular internet connection. ISDN is a dial-up technology, so with an ISDN modem you can dial directly to another ISDN modem and get up to 128Kbytes/sec of bandwidth. See more here.

LAN

Local Area Network. It's a bunch of computers in reasonable physical proximity interconnected to each other, usually with 10baseT ethernet and a hub. A WAN is used to connect one LAN to another over a large distance.

Router

A Router can be either a box or some software that you run on a PC (Macs included, of course.) Routers are used as traffic directors between two networks, like between your local LAN and your ISP. For more details, see Routers and Hubs.

WAN

Wide Area Network. A network used to connect physically distance networks (LANS) together. The entire Internet can be thought of as a WAN. WANs generally involve telcos, like AT&T, carriers like UUnet or Qwest, frame relay or microwave links.