Download Local-Area Networks

COMPUTER
NETWORKS
Computer Networks
A series of
electronic devices
connected
together through
copper cables,
fiber optics, and
radio waves.
Computer Networks
There are many types of computer
networks, including:
 Local-Area Networks (LAN's): The
computers are geographically close to
each other (in the same building).
 Wide-Area Networks (WAN's): The
computers are farther apart and are
connected by telephone lines or radio
waves.
 Metropolitan-Area Networks (MAN's): A
MAN is usually not privately owned by the
user or the company.
Local-Area Networks
(LAN's):
two buildings with 4 departments connected
as a LAN.
Wide-Area Networks (WAN's):
A WAN would
be most useful
for large
companies with
offices or
factories in
widely
separated
areas
INTERNET – A type of WAN
Computer Networks
In addition to these types, the
following characteristics are
also used to categorize
different types of networks:

topology

architecture

protocol
Computer Networks
topology :
 The geometric arrangement of
a computer system.
 Common topologies include a
mesh,star,bus, ring,tree.
Topology refers to the shape
of a network, or the network's
layout.
Topologies are either
physical or logical.
Physical Topology
The physical layout of devices on a
network.
Every LAN has a topology, or the way
that the devices on a network are
arranged and how they communicate
with each other.
The way that the workstations are
connected to the network through
the actual cables that transmit data.
Logical Topology
The way that the signals act on the
network media,
or the way that the data passes
through the network from one device
to the next without regard to the
physical interconnection of the
devices.
Network Topology
The five most common network
topologies.
 Mesh
 Star
 Bus
 Ring

Tree
Mesh Topology
In a true mesh topology
every node has a
connection to every
other node in the network.
Star Topology
Nodes communicate
across the network by
passing data through
the hub.
All devices are
connected to a
central hub.
Bus Topology
All devices are
connected to a central
cable, called the bus
or backbone.
Ring Topology
All devices are
connected to one
another in the shape of
a closed loop, so that
each device is
connected directly to
two other devices, one
on either side of it.
Tree Topology
A hybrid topology.
Groups of starconfigured networks
are connected to a
linear bus backbone.
Computer Networks
architecture
Networks can be broadly
classified as using either a
 peer-to-peer or
 client/server
Network Architecture
peer-to-peer
Sharing single
computers with
each other.
peer-to-peer
 One individual can access and
save files to another
individuals computer.
 This can be slow when large
files are being transferred.
client/server
 A single computer is set aside to only save files
and run programs.
 Each computer in the network can run any
program, or save files, to this single computer,
which is named the server.
 Computers on a network are
sometimes called nodes, a
processing location.
 Every node has it's own unique
network address.
 Computers and devices that
allocate resources for a
network are called servers.
Computer Networks
protocols
For two computers to talk to each
other, they must agree on some
kind of standard way of
communicating.
Computer Networks
 computers on a network will not be able
to communicate unless they are able to
speak the same "language."
 The
languages by which computers
communicate over a network are called
protocols.
protocol
 Protocols tell computers how to send
and receive data and what to do with
the data after they receive it.
 The protocol defines a common set of
rules and signals that computers on
the network use to communicate.
Computer Networks
Modern computer networks use
standard protocol called Ethernet
to communicate with one another.
Ethernet
 One of the most popular protocols
for LAN's is called Ethernet, a localarea network (LAN) protocol
developed by Xerox Corporation in
cooperation with DEC and Intel in
1976.
Ethernet
 Ethernet uses a bus or star topology
and supports data transfer rates of
10 Mbps.
 It is one of the most widely
implemented LAN standards.
 Another popular LAN protocol for
PC's is the IBM token-ring network.
Ethernet
Ethernet is a technology used to
connect multiple devices together to
form a "network", it consists of physical
cables, connectors, and a protocol that
allows clear communications between
devices.
Ethernet run at either 10, 100 or 1000
megabits per second.
Cable and Hardware
Ethernet has
several wiring
standards that
dictate the speed
and the
communications
medium the
computers will
use.
Cable Type & Speed
Name
10Base-2
Cable Type
Coaxial
Speed
10Mbps
10Base-T
CAT3 or CAT5
10Mbps
10Base-F
Twisted Pair
Fiber optic
10Mbps
100Base-T (Fast Ethernet)
CAT5 Twisted Pair
100Mbps
1000Base-T (Gigabit Ethernet)
Fiber optic
1000Mbps
Network Channels
There are three main cable types:
Coaxial, which looks like TV antenna
wire,
Twisted pair; which looks like phone
wire; and
Fiber optic wire.
Types of cables
Coaxial
Coaxial cable is
classified into two
categories:
 baseband
(uses
digital signals)
and
 broadband (uses
analog signals)
coaxial cable
Coaxial
A single insulated inner wire is
surrounded by a cylindrical conductor
which is covered with a shield; it
transmits electromagnetic signals.
Types of cables
Twisted Pair
two insulated
copper wires
twisted together in
a regular spiral
pattern;
one pair
establishes one
communication
link;
it transmits
electromagnetic
signals.
Twisted pair
Twisted pairs are
distinguished
between
shielded (STP) &
unshielded (UTP)
twisted pairs
according to their
protection against
electromagnetic
fields
Types of cables
Fiber optic
transmits optical
signals, which
must be
transformed to
electromagnetic
signals
Fibre Optic
consists of three concentric sections,
the core (a fibre conducting optical rays),
the cladding (reflecting optical rays) and
 the jacket (surrounding one or many fibres
to protect them)
Wireless Networks
Wireless networks are
perfect when you don’t
feel like stringing a
bunch of cable over you
floor.
They also have the
added advantage that
your
computer
(or
laptop) can be “on the
go” anywhere in the
house.
However, they are quite
expensive.
Other network hardware
Besides wire, you will need
network cards for each machine on
a network, and a hub
Hub
The most important
piece of your network is
the hub.
It is the heart of any
10/100 Base-T network.
All computers on the
network are connected
to the hub.
Hub
It is the job of the
hub to broadcast a
signal send from one
machine to all the
machines on the
network.
The hub also isolates
a computer if it
detects a cable fault.
Hub
Hubs come in many
sizes, ranging from 4
ports all the way up to
36 ports.
Each port can be used
to connect a computer.
The more ports, the
more computers you
can connect.
Obviously, the more
ports, the higher the
price.
The network card
The last piece of hardware you will need is
network interface cards (or NICs) for each
machine in your house.
The network card
This card is used to communicate on
the network.
Some computers, such Macintoshes,
already come pre-installed with
network cards.
The network card
You can tell if your computer has a
network card build in by looking in
the rear of the case for a jack that
looks kind of like a phone jack,
only bigger.
Network cards come in three flavors:
10Base-T,
 10/100Base-T
 100Base-T.

The network card
10Base-T Ethernet
The primary type of Ethernet in use today is
10Base-T, which operates at 10 Mbps and
follows a star topology using unshielded
twisted-pair cabling.
10Base-T Ethernet networks are very easy to
set up. This flavor of Ethernet relies on hubs.
The network card
100Base-T cards cost only a little more
than ones that operate at 10 Mbps, and
give you much more flexibility for
upgrading your network in the future.
Most 100Base-T hubs will automatically
sense whether the card connected to each
port is 10 or 100 Mbps and operate
accordingly.
ARCNET
Short for Attached Resource Computer
network, ARCnet is one of the oldest,
simplest, and least expensive types of
local-area network.
ARCnet was introduced by Datapoint
Corporation in 1977.
It uses a token-ring architecture, supports
data rates of 2.5 Mbps, and connects up to
255 computers.
Token ring
is a local area network (LAN) in
which all computers are connected in
a ring or star topology and a bit- or
token-passing scheme is used.
This prevents the collision of data
between two computers that want to
send messages at the same time.
The Token Ring protocol is the
second most widely-used protocol
on local area networks after Ethernet.
ARCNET
A special advantage of ARCnet is
that it permits various types of
transmission media i.e
twisted-pair wire,
 coaxial cable, and
 fibre optic cable

to be mixed on the same network.
Summar
y
Types of Networks:
LAN
WAN
MAN
Network Topology:
Mesh
Star
Bus
Ring
Tree
Network Interface Card:
Ethernet
Arcnet
Channels:
Twisted pair
Coaxial
Fibre optic
Server
Nodes
Hubs