What is a Computer Network
Computer networking is the engineering discipline concerned with
communication between computer systems or devices.
Networking,
routers,
routing protocols,
and
networking over the public Internet have their specifications
defined in documents called RFCs.
A computer network is any set of computers or devices connected to
each other. Examples of networks are the Internet, or a small home local
area network (LAN) with two computers connected with standard networking
cables connecting to a network interface card in each computer. All
modern aspects of the Public Switched Telephone Network (PSTN) are
computer-controlled, and telephony increasingly runs over the Internet
Protocol, although not necessarily the public Internet.
Views of networks
Network administrators see
networks from both physical and logical
perspectives. The physical perspective involves geographic locations,
physical cabling, and the network elements (e.g.,
routers,
bridges and
application layer gateways that interconnect the physical media. Logical
networks, called, in the TCP/IP architecture, subnets , map onto one or
more physical media. For example, a common practice in a campus of
buildings is to make a set of
LAN cables in each building appear to be a
common subnet, using virtual
LAN (VLAN) technology.
Basic Hardware Components
All networks are made up of basic hardware building blocks to
interconnect network nodes, such as Network Interface Cards (NICs),
Bridges,
Hubs,
Switches, and
Routers. In addition,
some method of connecting these building blocks is required, usually in
the form of galvanic cable (most commonly Category 5 cable). Less common
are microwave links (as in IEEE 802.11) or optical cable ("optical
fiber").
Network Interface Cards
A network card, network adapter or NIC (network interface card) is a
piece of computer hardware designed to allow computers to communicate
over a computer network. It provides physical access to a networking
medium and provides a low-level addressing system through the use of MAC
addresses. It allows users to connect to each other either by using
cables or
wirelessly.
Repeaters
A repeater is an
electronic device that receives a signal and retransmits it at a higher
level or higher power, or onto the other side of an obstruction, so that
the signal can cover longer distances without degradation.
Network Hub
A hub
contains multiple ports. When a packet arrives at one port, it is copied
the packets to all the ports of the
hub. When the packets are copied,
the destination address in the frame does not change to a broadcast
address. It does this in a rudimentary way, it simply copies the data to
all of the Nodes connected to the
hub.
Network Bridge
A network bridge
connects multiple network segments at the data link layer (layer 2) of
the OSI model. Bridges do not promiscuously copy traffic to all ports,
as does a hub. but learns which MAC addresses are reachable through
specific ports. Once the bridge associates a port and an address, it
will send traffic for that address only to that port. Bridges do send
broadcasts to all ports except the one on which the broadcast was
received.
Network Switch
Switches are
a marketing term that encompasses
routers and
bridges, as well as
devices that may distribute traffic on load or by application content
(e.g., a Web URL identifier).
Switches may operate at one or more OSI
layers, including physical, data link,
network, or transport (i.e.,
end-to-end). A device that operates simultaneously at more than one of
these layers is called a multilayer switch.
Routers
Routers are the
networking device that forwards data packets along
networks by using
headers and forwarding tables to determine the best path to forward the
packets. Routers work at the network layer (layer 3) of the OSI model.
Routers also provide interconnectivity between like and unlike media.
This is accomplished by examining the Header of a data packet. They use
routing protocols such as Open Shortest Path First (OSPF) to communicate
with each other and configure the best route between any two hosts. A
router is connected to at least two
networks, commonly two
LANs or
WANs
or a LAN and its
ISP's network. Some DSL and Cable Modems have been
integrated with routers for home consumers.
Source: http://www.wikipedia.org
