Full and Half-Duplexing
There are three different terms used to
describe how transmitters and receivers interact during
communications, simplex, half-duplex, and full-duplex. In simplex
communications, the data travels only one way and no response is
needed or possible. An example of simplex is a school Public Address
(PA) system. In half-duplex communications, data travels from a
transmitter to a receiver, then from the receiver to the transmitter,
repeatedly, however, never simultaneously - simultaneous transmission
and reception of data is not possible. Examples of half-duplex are
walkie-talkies and 10BASE-T Ethernet. In full-duplex communications,
both transmitter and receiver may send and receive simultaneously.
Clearly this is the fastest way to communicate, but requires more
sophisticated electronics. Examples of full duplex are the telephone
and 100BASE-TX (Fast Ethernet).
WAN and LAN
A Wide Area Network (WAN) is
geographically unlimited; while, a Local Area Network (LAN) is limited
to a smaller region. WANs can span over a cities, countries, and
multiple locations; LANs are limited to a single building or school
campuses.
LANs operate within a limited
geographic area, such as a single building, connecting workstations,
peripherals, and other devices on a single network. LANs provide a
business with complete computer technology to share devices on a
network.
WANs are geographically unlimited and
vary in size, between cities, states, or even globally. WANs provide
an efficient way to move information from one network (a LAN) to
another network.

Server, Workstation, and Host
Servers are typically powerful
computers, which provide resources and services to other computers on
a network. Workstations (clients) are devices, which are capable of
local processing of data, and use resources and services provided by
the server. Host is the special name given to ANY addressable computer
system on a network running TCP/IP, examples of hosts include
workstations, servers, minicomputers, mainframes, and even routers.
Server-Based Networking and
Peer-To-Peer Networking
Two types of networks are Server-Based
and Peer-to-Peer. A server-based network, also known as
client/server, connects numerous hosts to a centralized computer. This
computer serves as a server, providing security functions and access
to the network and resources, allowing for a central security system.
As the network grows and the number of nodes increase, this type of
network can add specific servers to address to specific needs and
resources. Examples include file and print servers, application
server, domain controllers, and directory servers.
Client-Server networks require
typically a powerful server computer, running a network operating
system, and administration by highly trained personnel. Advantages are
the variety of services that can be provided and the central
administration of those services; however, the disadvantages include
cost and complexity.
In a peer-to-peer network, there is no
centralized server or security system. Each node on the network works
as its own server, granting permission to the other nodes on the
network to access its resources. This type of network is limited to
approximately 10 nodes connected to each other. Advantages include
simplicity, low cost, and ease of administration, while disadvantages
include slow speed and a severely limited range of services that can
be provided.
Cable, NIC, and Router
In order to create a properly
functioning network, the main necessities required include cables,
NICs, and routers. A cable is the physical media used to wire
networks. The cables that can be used to wire a network include
unshielded and shielded twisted pair (UTP and STP), coaxial, fiber
optic, or wireless (if no cables are required). These physical media
are used in combination with the network interface card (NIC), which
allows the computer to communicate with the network. Another way to
look at the NIC is that it allows the workstation Operating System
(OS) to communicate with the local area network operating system (NOS).
A router is a layer 3 device which performs best path selection and
packet switching, and is used to connect one or more Local Area
Networks (LAN) together to create a Wide Area Network (WAN).
Broadband and Baseband
Two types of signaling are Broadband
and Baseband. Broadband is an analog signaling technique normally used
in cable television. This type of signaling can carry video, voice,
and data across a wire. It shares the medium's bandwidth over
different channels, often using different carrier frequencies. One
sharing technique is called frequency division multiplexing (FDM).
Baseband is a digital signaling
technique, which uses the entire medium's bandwidth for a single
channel at a time and allows very high throughputs (the actual
measured bandwidths are possible due to this single-channel-at-a-time
technique). Signals are in the form of voltage pulses on copper, light
pulses on optical fiber, or electromagnetic waves in the atmosphere. A
form of multiplexor (MUX) device is usually required so that multiple
devices can take their turns using the medium.
Gateway
A gateway, which works as a translator,
provides communication between different operating systems and
frequently services the Internet. A gateway must exist if two
different types of operating systems, such as Windows and UNIX, are to
communicate. In order to communicate with node on a different network
over the Internet, the device must be connected to a LAN or a dial up
connection.
Gateway also refers to default gateway,
an IP address is used to forward packets from one subnet to another
subnet, if there is no other routing information available.
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