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.

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.

Internet

A "public" communications network using TCP/IP protocols. To access the Internet, you must be running TCP/IP at the point of connection and you must arrive there with a unique IP address - a "quad-dot" number like 216.71.126.178. Each of the four numbers ranges from 0 to 255. No other machine in the world has the same address. TCP/IP requires that you send a "packet" addressed to a machine with another IP address. The internet will do all the routing to get it there. If one route breaks down, it will find another. Packets are re-assembled in the right order at the other end. It's magnificent.

Intranet

A "private" version of the Internet. Typically a TCP/IP network running within a company that excludes access from computers not connected directly to the company's network.

MAE-West

And MAE-East. These are major connection points between ISPs. MAE-West is located in Santa Clara, CA; MAE-East is in Virginia. Most internet traffic goes through one of these major switching points. The exception is where one ISP has a direct connection to another ISP. (Called "peering".) That traffic doesn't have to go through MAE. MAE can be a bottleneck.

T-1

T1 is a 1.5 Mbit/second internet connection. Most companies have at a connection at least this fast. There are also T3 connections, which are faster yet, and OC3, which is an optical fiber protocol that's faster yet. ISPs use high performance fiber connections between each other.

TCP/IP

The protocol of the internet - by definition. The IP stands for "Internet Protocol". The TCP is something else I can't remember. TCP/IP works off a few very simple principles:

• Every connected machine has a unique 32-bit address, usually expressed as a "quad-dot" like 216.71.1267.178.
• Transmission are made in fairly small packets of bits, with headers containing the source and destination IP addresses.
• The network consists of routers each of which will forward the packet to a router closer to the destination. If the packet doesn't get through, it will try another path. Eventually, unless the whole network is down, the packet will get through.

TCP/IP is way cool.

VPN

Virtual Private Network. A VPN is created when a company uses the public Internet to connect its sites, and encrypts the traffic so that others cannot understand the contents of packets. A VPN replaces a dedicated (expensive) connection between two locations with a (cheap) internet connection.

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.