4. Router
A router is an electronic device and/or software that connects
at least two networks and forwards packets among them according
to the information in the packet headers and routing tables. Routers
are fundamental to the operation of the Internet and other
complex networks (such as enterprise-wide networks).
A network consists of two or more computers, and typically
other devices as well (such as printers and external hard drives),
that are linked together so that they can communicate with each
other and thereby share files and the devices. Examples of the
networks connected by a router can be two LANs (local area
networks) or WANs(wide area networks) or a LAN and its ISP's
(Internet service provider's) network.
6. modem
A modem (modulator-demodulator) is a device
that modulates an analog carrier signal to encode digital
information and demodulates the signal to decode the transmitted
information. The goal is to produce a signal that can be transmitted
easily and decoded to reproduce the original digital data. Modems
can be used with any means of transmitting analog signals,
from light emitting diodes to radio. A common type of modem is one
that turns the digital data of a computer into modulated electrical
signal for transmission over telephone lines and demodulated by
another modem at the receiver side to recover the digital data.
8. Hub (ฮับ)
An Ethernet hub, active hub, network hub, repeater
hub, multiport repeater or hub is a device for connecting
multiple Ethernet devices together and making them act as a
single network segment. It has multipleinput/output (I/O) ports, in
which a signal introduced at the input of anyport appears at the
output of every port except the original incoming. A hub works at
the physical layer (layer 1) of the OSI model. Repeater hubs also
participate in collision detection, forwarding a jam signal to all ports
if it detects a collision.
