1 introduction-to-computer-networking

DefinitionDefinition
 A computer network is a group of
interconnected computers.
 It allows computers to communicate with
each other and to share resources and
information

ComponentsComponents
 A minimum of at least 2 computers
 Cables or wireless communication that
connect the computers to each other.
 A network interface device on each computer
(this is called a network interface card or NIC)
 A ‘Switch’ used to switch the data from one
point to another.
 Network operating system software.

Types of networkTypes of network
The three basic types of networks include:
 Local Area Network (LAN)
 Metropolitan Area Network (WAN)
 Wide Area Network (WAN)

Local Area Network (LAN)
 A LAN covers a relatively small area such as a
classroom, school, or a single building
 LANs are inexpensive to install and also
provide higher speeds.

Metropolitan Area Network (MAN)
 A MAN spans the distance of a typical
metropolitan city
 The cost of installation and operation is higher
 MANs use high-speed connections such as
fiber optics to achieve higher speeds.

Wide Area Network (WAN)
 WANs span a larger area than a single city.
 These use long distance telecommunication
networks for connection, thereby increasing
the cost.
 The Internet is a good example of a WAN.

Network Configuration
Classification based on how computers
behave in a network
Two classifications are:
 Peer-to-Peer networkPeer-to-Peer network
 Server based networkServer based network

Peer-to-Peer Networks
 In a peer-to-peer
network, the networked
computers act as equal
partners, or peers, to
each other.
 As peers, each computer
can take on the client
function or the server
function alternately.

Client/Server Networks
 In a client/server network
arrangement, network
services are located in a
dedicated computer whose
only function is to respond to
the requests of clients.
 The server contains the file,
print, application, security,
and other services in a
central computer that is
continuously available to
respond to client requests.

Networking hardware
 Hub – electronic device (with a number of ports) used
in a LAN to link groups of computers
 Repeaters (also called amplifiers) – electronic devices
that receive signals and amplify and send them along
the network
 Routers - electronic devices used to ensure
messages are sent to their intended destinations
 Gateway – consists of hardware and/or software that
allows communications between dissimilar networks
 Bridge – consists of hardware and/or software
that allows communication between two
similar networks

Network Topologies
 A network topology describes the layout of the
wire and devices as well as the paths used by
data transmissions.
Bus TopologyBus Topology
 Also called linear bus
 One wire connects all
nodes
 Terminator ends the
wires

Network Topologies
Star TopologyStar Topology
 All nodes connect to a hub
Packets sent to hub
Hub sends packet to
destination
Ring TopologyRing Topology
 Nodes connected in a circle
 Tokens used to transmit
data

Network Topologies
Mesh TopologyMesh Topology
 All computers connected
together
 Internet is a mesh network
Tree TopologyTree Topology
 Hierarchal Model
 Combines characteristics of
linear bus and star topologies.

Communications Media
 Communications ChannelCommunications Channel
To transfer data from one computer to
another requires some type of link through
which the data can be transmitted. This link
is known as the communications channel.
To send data through the channel requires
some type of transmission media, which
may be either physical or wireless.

Physical Media
Twisted-pair cableTwisted-pair cable
 Pair of insulated copper wires
 Types
 Shielded(STP)
 Unshielded(UTP)
 UTP common in LAN
 Max. cable length – 100 meters
 Least expensive type of cable
 Used in many telephone systems

Physical Media
Co-axial cableCo-axial cable
 Consists of an insulated
center wire grounded by a
shield of braided wire
 Carries data as
electromagnetic signals
 Good resistance against
interference
 Used by the cable
television industry

Physical Media
Fiber optic cableFiber optic cable
 Core – cylinder of glass
 Bandwidth is greater, so it
can carry more data
 Not subject to interference
 Transfer rate – more than
100 mbps
 Expensive

Wireless Media
Microwave systemMicrowave system
– transmits data via high-frequency
radio signals through the atmosphere
Satellite systemSatellite system
– receive transmitted signals, amplify
them, and then transmit the signals
to the appropriate locations

Wireless Media
Cellular technologyCellular technology
– uses antennae resembling telephone
towers to pick up radio signals within
a specific area (cell)
Infrared technologyInfrared technology
– transmits data as infrared light waves
from one device to another, providing
wireless links between PCs and
peripherals

InternetworkInternetwork
An Internetwork is the connection of two
or more distinct computer networks or
network segments via a common routing
technology.
Any interconnection among or between
public, private, commercial, industrial, or
governmental networks may also be
defined as an internetwork.

Intranet
An intranet is a private LAN designed for
use by everyone within an organization.
An intranet might consist of an internal
e-mail system, a message board and
one or more Web site portals that
contain company news, forms, and
personnel information

Extranet
A network that connects people
within your company with people
who are outside your company--all
within a secure, password-protected
network that can be accessed from
anywhere.

Internet
A computer network consisting of a
worldwide network of computer
networks that use the TCP/IP
network protocols to facilitate data
transmission and exchange

Internet Connections
Internet backbone : A set of high-speed
networks that carry Internet traffic.
These networks are provided by companies
such as AT&T, GTE, and IBM
Internet service provider (ISP) : A
company that provides other companies or
individuals with access to the Internet

 There are various technologies available that you can
use to connect a home computer to the Internet
 A phone modem converts computer data into an
analog audio signal for transfer over a telephone
line, and then a modem at the destination converts
it back again into data
 A digital subscriber line (DSL) uses regular
copper phone lines to transfer digital data to and
from the phone company’s central office
 A cable modem uses the same line that your cable
TV signals come in on to transfer the data back and
forth

 Broadband A connection in which transfer
speeds are faster than 128 bits per second
 DSL connections and cable modems are
broadband connections
 The speed for downloads (getting data from
the Internet to your home computer) may not
be the same as uploads (sending data from
your home computer to the Internet)

Packet Switching
 To improve the efficiency of transferring information
over a shared communication line, messages are
divided into fixed-sized, numbered packets
 Network devices called routers are used to direct
packets between networks

Open System Interconnection (OSI)
 The International
Organization for
Standardization (ISO)
established the Open
Systems
Interconnection (OSI)
Reference Model
 Each layer deals with a
particular aspect of
network communication

Network Protocols
Network protocols are layered such that
each one relies on the protocols that
underlie it
Sometimes referred to as a protocol
stack

TCP/IP Protocol
 TCP stands for Transmission Control
Protocol
 TCP software breaks messages into packets,
hands them off to the IP software for delivery,
and then orders and reassembles the packets
at their destination
 IP stands for Internet Protocol
 IP software deals with the routing of packets
through the maze of interconnected networks to
their final destination

 Other protocols build on the foundation
established by the TCP/IP protocol suite
Simple Mail Transfer Protocol (SMTP)
File Transfer Protocol (FTP)
Telnet
Hyper Text Transfer Protocol (HTTP)

Network Security
 Firewalls can either be hardware and/or software
based.
 It sits at the gateway between the two networks,
usually a private network and a public network such as
the internet.
 All traffic from inside to outside and vice versa, must
pass through the firewall.
 Only authorized traffic as defined by the local security
policy, will be allowed to pass.
 The firewall itself is immune to penetration.

1 introduction-to-computer-networking

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