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Network Terminology

Access point: The hardware interface between a wireless LAN and a wired LAN. The access point attaches to the wired LAN through an Ethernet connection. Today, many residential routers and gateways incorporate access points.

Cable modem: Hardware that allows high-speed Internet access over a cable television line.

Category 5 cable: Wiring certified to have the characteristics necessary for the transmission of Ethernet signals at 10 Mbps, 100 Mbps, and 1 Gbps.

DHCP (Dynamic Host Configuration Protocol): A specification for the service provided by a router, gateway, or other network device that automatically assigns an IP address to any device that requests one.

DOCSIS (Data Over Cable Service Interface Specification): A relatively new industry standard that defines how cable modems communicate over cable TV lines. Any DOCSIS-compatible modem will work on any DOCSIS-compatible cable TV network.

DSL (digital subscriber line): A type of digital connection between a customer’s facility and a telephone company’s central office. DSL supports high-bandwidth transmissions over traditional telephone wires. Data rates can reach several hundred kilobits per second in the download direction. Like a cable modem, DSL is always on, but unlike with a cable modem, the local connection is not shared within a neighborhood. This gives DSL more consistent throughput–but lower peak throughput–than most residential cable modem installations.

802.11b: A standard for wireless local area networks. It provides for transmissions at up to 11 Mbps in the 2.4-GHz band. Also referred to as Wi-Fi.

Ethernet: The most popular LAN communication technology. There are a variety of types of Ethernet, including 10 Mbps (traditional Ethernet), 100 Mbps (Fast Ethernet), and 1,000 Mbps (Gigabit Ethernet). Most Ethernet networks use Category 5 cabling to carry information, in the form of electrical signals, between devices.

Hub: A hardware device that provides a central point for the connection of Ethernet cables from workstations and other network devices. Hubs work on a contention scheme, which means that all connected devices must share the available communication capacity (or bandwidth). This can result in a slowing of communication to individual devices and an overall reduction in throughput. Because this is not the case with switches, which cost little more than hubs, we recommend using switches in every application.

IP: (Internet Protocol) The standard that describes the layout of the basic unit of information on the Internet (the packet) and also details the numerical addressing scheme used to route that information. Your Internet service provider controls the IP address of any device it connects to the Internet. This includes cable modems, DSL modems, and systems connected through dial-up modems, for example. You can control the IP addresses inside your network, but they must conform to IP addressing rules. In large corporate networks, IP addressing is a job for experts. In smaller LANs, most people will allow the DHCP function of a router or gateway to assign the IP addresses on internal networks.

NAT: (network address translation) A technique, generally applied by a router, that makes many different IP addresses on an internal network appear to the Internet as a single address. For routing messages properly within your network, each device requires a unique IP address. But the addresses may not be valid outside your network. NAT solves the problem. When devices within your network request information from the Internet, the requests are forwarded to the Internet under the router’s IP address. NAT distributes the responses to the proper IP addresses within your network. As a byproduct, NAT has the effect of hiding your network resources, because the outside world sees only the router’s address. Hackers can penetrate NAT, but not without substantial effort. Most firewalls and routers offer some type of NAT, thus providing a powerful, secure interface (known as a proxy) to the Internet.

NIC: (network interface card) A plug-in adapter card that enables a computer to connect to a LAN.

Patch cable: An Ethernet cable wired in a way that allows it to link the Ethernet ports (connectors) on two PCs without a hub or switch in between. A patch cable is also used to link two switches, or to link a switch to a router, by connecting the port on each labeled uplink.

Residential gateway: A residential router.

RJ-11, RJ-45: Commonly used modular connectors. An RJ-11 connector attaches to telephones; the larger RJ-45 connector is used for Ethernet cable connections. Each type has 8 pins.

Router: An interconnection device that links a local network to the outside world. A router uses a networking protocol, such as IP, to address and direct packets of data flowing into and out of the network. A router may also integrate firewall, DHCP, NAT, and filtering capabilities. Routers come in many different capacities and offer a variety of features. A small router, designed for home and small-office use, typically has one Ethernet connection for a cable or DSL modem and another for the network. A router, also known as a residential gateway, may include a wireless access point.

Switch: A hardware device that serves as a central connection point for all network cables. Unlike the situation with a hub, the devices connected to a switch do not share the network communication capacity (bandwidth); each device connected to a switch receives the full network bandwidth. Switches can be standalone devices the size of paperback books, or devices integrated into racks of equipment. In relatively small networking environments, a switch of 4 to 12 ports may be part of a router or gateway.

Virtual private network (VPN): A communications system that uses authentication, encryption, and data-packaging technology to allow private network traffic to travel over the public Internet without being deciphered by unauthorized parties. VPNs provide remote-office and work-at-home users with secure access to a corporate LAN or WAN (wide area network).