A piece of data transmitted over a packet-based network, such as a TCP/IP network. Also called datagram.

All data transmitted over the Internet, for example, is transmitted via packets. Since each packet can take a different route to its destination, traffic loads on each individual route are reduced, thus improving network efficiency. When all packets arrive at the destination, the original message can be reassembled.

In the event that a packet does not reach its destination, the packet is resent along a different route. The term packet loss refers to how many packets (usually expressed as a percentage of the total number of packets) never made it to the final destination. Ideally, packet loss should be close to zero.


Peripheral Component Interconnect. A standard interface for connecting add-on cards to a computer. PCI slots are white, while older ISA slots are black.


A type of network in which each computer shares an equal load of network activity. Computers are interdependent, rather than dependent on a central server.


Packet Internet Groper. A small amount of data sent to test connectivity between two computers. Results depend on whether or not a response is received.


A software-based “hole” for data transmissions going to or from a computer.

There are exactly 65,536 ports, numbered sequentially from 0 to 65,535. Ports can either be open (communication allowed) or closed (communication not allowed).

Every Internet application uses a certain port or set of ports to communicate. FTP server software, for example, usually communicates on port 21. However, to allow it to operate through a NAT box, a user must “map” port 21 to the computer running FTP server software. That way, the NAT box knows to automatically forward all requests on port 21 to the specified computer, which allows the software to function as it normally should.

Even in situations without a NAT box, ports can be opened or closed for security reasons. This is most often accomplished thru the use of a firewall.


Point-to-Point Protocol over Ethernet. An authentication protocol commonly used by DSL providers to force their users to “log in” to the service. To be used through a router, PPPoE must be supported by the router’s firmware.


Point-to-Point Tunneling Protocol. A protocol designed for VPN. Commonly used to remotely connect to corporate networks. To be used through a router, PPPoE must be supported by the router’s firmware.


Any networking language that computers use to communicate.

The Internet is based on the TCP/IP protocol; common LAN protocols include NetBEUI and the older IPX/SPX. In Windows, protocols are indicated by gray cable icons.


A server located between end users and real servers that intercepts requests in order to speed fulfillment.

Proxy servers work by caching copies of pages that have already been accessed. For example, if user A requests, user A’s computer may actually contact a proxy server. The proxy server will then check to see if it has a copy of in its memory. If not, it contacts and requests the homepage, then turns around and sends it to user A. At the same time, the proxy server stores a copy of in its memory. A few minutes later, when user B requests, the proxy server can simply provide a copy from its memory bank; there is no need to actually contact again.

Since proxy servers are usually much closer to the end user than real servers, they can offer a significant increase in effective Internet speed.