LAN - A local area network (LAN) is a group of computers and associated devices that share a common communications line or wireless link and typically share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users (for example, in a home network) or as many as thousands of users (for example, in an FDDI network).

WAN - A wide area network ( WAN ) is a geographically dispersed telecommunications network . The term distinguishes a broader telecommunication structure from a local area network ( LAN ). A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network ( MAN ).

Network Hub - A hardware device providing the interconnection between networked devices. It is called a hub because the network wiring can be sketched like a spoked wheel with the hub at the center. A Network Hub is used with 10-Base T and 100-Base T EtherNet wiring. Hubs differ in the number of ports they have and in large networks multiple hubs can be bridged together.

Network Switch - A network switch is a computer networking device that connects network segments. It uses the logic of a Network bridge but allows a physical and logical star topology. It is often used to replace network hubs. A switch is also often referred to as an intelligent hub.

Network Router - A device that forwards data packets along networks . A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Routers are located at gateways , the places where two or more networks connect.

Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

Very little filtering of data is done through routers.

Ethernet - Ethernet is the most widely-installed local area network technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.

A newer version of Ethernet, called 100Base-T (or Fast Ethernet), supports data transfer rates of 100 Mbps. And the newest version, Gigabit Ethernet supports data rates of 1 gigabit (1,000 megabits) per second.

Firewall - A network firewall is a system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.
There are several types of firewall techniques:

Packet filter : Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.

Application gateway : Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.

Circuit-level gateway : Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.

Proxy server : Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses.

Wi-Fi: Short for wireless fidelity and is meant to be used generically when referring of any type of 802.11 network. Currently the most popular and widely used is 802.11G.

Networking Glossary - Page 2