The ABC of
Networking
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. 802.11a: A standard for wireless local area networks. It
provides for transmissions at up to 54 Mbps/up to 72 Mbps in the 5-GHz band.
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.
CAT5 Cable (Category 5): 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.
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.
Firewall: A hardware or software system that
enforces an access control policy between two networks. It can be
thought of as a pair of mechanisms: one to block traffic, and the
other to permit traffic.
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.
LAN (Local Area Network): A LAN is
a high-speed communications system designed to link computers and
other data processing devices together within a small geographic area
such as a workgroup, department, or a single floor of a multi-story
building.
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. Print
Server: An interconnection device that links a
LAN or WAN to printer(s) that allow multiple
users on the same network to share one or more printers
Residential Gateway: A residential router.
RJ-11, RJ-45: Commonly used modular connectors. An RJ-11
connector that has 4 pins attaches to telephones; the larger RJ-45 connector
with 8 pins is used
for Ethernet cable connections.
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).
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