Download Introduction to Networking

Unit III
Data Communication and
Networks
(ITM)
Ashima Wadhwa
Assistant Professor (giBS)
Overview of Networks


Network – two or more computers linked
together so they can communicate, share
resources and exchange information
Networks allow users to:
◦
◦
◦
◦
◦
◦
Access shared programs and data
Transfer data from one computer to another
Share peripheral devices such as printers
Share storage devices to store data for backup
Use e-mail to communicate with one another
Access the Internet
Networking

Computer network A collection of
computing devices that are connected in
various ways in order to communicate
and share resources
Usually, the connections between
computers in a network are made using
physical wires or cables
However, some connections are wireless,
using radio waves or infrared signals
153
Networking
The generic term node or host refers to
any device on a network
 Data transfer rate The speed with
which data is moved from one place on a
network to another
 Data transfer rate is a key issue in
computer networks

154
Networking

Computer networks have opened up an entire
frontier in the world of computing called the
client/server model
155
Advantages:
› Enable people to work together
› Reduce costs from sharing networked
hardware and software
› Increase productivity by sharing data
› Provide access to a wide range of services
and specialized peripheral devices
Disadvantages
› Unavailable resources when network malfunctions
› More vulnerable to unauthorized access than
stand alone computers
› Susceptible to an increased number of worms,
Trojan horses, and blended threats
Types of Networks
LAN
 WAN

Local Area Network (LAN)
Network of computers located in a single
location, like a home, school, or office
building
 Can share connection with other LANS
and with the internet

Characteristics of a LAN?
Local area network
 Relatively limited in size
 Computers connected in small areas
 Same office
 True peer-to-peer
 Can support limited number of nodes

Wide Area Network (WAN)

Network over a large area like a city, a
country, or multiple countries
◦ Connects multiple LANs together
Generally utilizes different and much
more expensive networking equipment
than LANs
 The internet is
the most
popular WAN

Types of Computer Networks :
Wired and Wireless Networks
 Client / Server And Peer to Peer
Networks

Wired Network
A wired network uses cables to connect
network devices
 Wired networks are fast, secure, and
simple to configure
 Devices tethered to cables
have limited mobility

Wireless Networking
A network is considered wireless when data is
transmitted from one device to another without
cables or wires
 Tend to be slower than wired networks
 Have more security issues
 Common wireless terms:

› Wi-Fi - common standard technology for building home
networks and other LANs
› Hotspots – many businesses use Wi-Fi technology to
allow the public an access point to a wireless network
› Bluetooth – allows handhelds, cell phones, and other
peripherals to communicate over short ranges
Client/Server Network
work devices can function as clients or servers

Server - computer that performs
administration or coordination functions
within a network
 Types: (1)application server, (2) file server, (3)

print server
Client – regular workstation that performs
applications
Client / Server Networks

Clients
◦ Computers that request or order information
from a server
◦ Usually desktop computers with their own
local storage and processing power
◦ Thin client – network computer with no local
storage

Servers
◦ Computers that work behind the scenes to
provide (serve) the resources requested by the
clients
◦ Two types
 Non-dedicated – provides many different services to
its client computers such as file retrieval, printing,
and emailing
 Dedicated – provides only one type of resource to
its clients, such as printing
Client/Server Network
Peer-to-Peer Network
A network of personal computers, each of
which acts as both client and sever, so that
each can exchange files directly with every
other computer on the network
 Each computer can access any of the others,
although access can be restricted to those
files that a computer's user chooses to
make available
 Less expensive than client/server networks
but less efficient when large amounts of
data need to be exchanged

Peer-to-peer
Topology

A Network Topology is the way computer
systems or network equipment
connected to each other. Topologies may
define both physical and logical aspect of
the network. Both logical and physical
topologies could be same or different in a
same network.
Topology

Common types:
◦
◦
◦
◦
◦
◦
Star
Ring
Bus
Tree
Mesh(Fully Connected)
Hybrid
Star Topology

All the cables run from the computers to a
central location, where they are all connected
by a device called a hub. Each computer on a
star network communicates with a central
hub that resends the message either to all the
computers or only to the destination
computers.
Advantages of Star topology
▸ Due to its centralized nature, the topology offers
simplicity of operation.
▸ It also achieves isolation of each device in the
network.
▸ Adding or removing network nodes is easy, and can
be done without affecting the entire network.
▸ Due to the centralized nature, it is easy to detect
faults in the network devices.
▸ As the analysis of traffic is easy, the topology poses
lesser security risk.
▸ Data packets do not have to pass through many
nodes, like in the case of a ring network. Thus, with
the use of a high-capacity central hub, traffic load can
be handled at fairly decent speeds.
Disadvantages of Star Topology
▸ Network operation depends on the
functioning of the central hub. Hence,
central hub failure leads to failure of the
entire network.
▸ Also, the number of nodes that can be
added, depends on the capacity of the
central hub.
▸ The setup cost is quite high.
Ring Topology
 Every
device has exactly two neighbors
for communication purposes
 All messages travel through a ring in
the same direction (either "clockwise"
or "counterclockwise“)
Advantages of Ring topology
▸ The data being transmitted between two nodes
passes through all the intermediate nodes. A central
server is not required for the management of this
topology.
▸ The traffic is unidirectional and the data transmission
is high-speed.
▸ In comparison to a bus, a ring is better at handling
load.
▸ The adding or removing of network nodes is easy, as
the process requires changing only two connections.
▸ The configuration makes it easy to identify faults in
network nodes.
▸ In this topology, each node has the opportunity to
transmit data. Thus, it is a very organized network
topology.
▸ It is less costly than a star topology.
Disadvantages of Ring Topology
▸ The failure of a single node in the network can
cause the entire network to fail.
▸ The movement or changes made to network
nodes affect the entire network's performance.
▸ Data sent from one node to another has to
pass through all the intermediate nodes. This
makes the transmission slower in comparison to
that in a star topology. The transmission speed
drops with an increase in the number of nodes.
▸ There is heavy dependency on the wire
connecting the network nodes in the ring.
Bus Topology
A
common backbone (a single cable)
to connects all devices and devices
attach, or tap into, the cable with an
interface connector
 Devices wanting to communicate
with other devices on the network
send a broadcast message onto the
wire that all other devices see, but
only the intended recipient actually
accepts and processes the message
Advantages of Bus topology
▸ It is easy to set up, handle, and
implement.
▸ It is best-suited for small networks.
▸ It costs very less.
Disadvantages of Bus Topology
▸ The cable length is limited. This limits the number
of network nodes that can be connected.
▸ This network topology can perform well only for a
limited number of nodes. When the number of
devices connected to the bus increases, the efficiency
decreases.
▸ It is suitable for networks with low traffic. High
traffic increases load on the bus, and the network
efficiency drops.
▸ It is heavily dependent on the central bus. A fault in
the bus leads to network failure.
▸ It is not easy to isolate faults in the network
nodes.
▸ Each device on the network "sees" all the data
being transmitted, thus posing a security risk.
Tree Topology
 Tree Topology
integrates the
characteristics of Star and Bus
Topology.
Advantages of Tree topology
▸ The tree topology is useful in cases where a star or bus
cannot be implemented individually. It is most-suited in
networking multiple departments of a university or
corporation, where each unit (star segment) functions
separately, and is also connected with the main node (root
node).
▸ The advantages of centralization that are achieved in a star
topology are inherited by the individual star segments in a
tree network.
▸ Each star segment gets a dedicated link from the central
bus. Thus, failing of one segment does not affect the rest of
the network.
▸ Fault identification is easy.
▸ The network can be expanded by the addition of
secondary nodes. Thus, scalability is achieved.
Disadvantages of Tree Topology
▸ As multiple segments are connected to a
central bus, the network depends heavily on
the bus. Its failure affects the entire network.
▸ Owing to its size and complexity,
maintenance is not easy and costs are high.
Also, configuration is difficult in comparison
to that in other topologies.
▸ Though it is scalable, the number of nodes
that can be added depends on the capacity
of the central bus and on the cable type.
Mesh Topology

In a mesh network
topology, each of the
network node,
computer and other
devices, are
interconnected with
one another.
Advantages of Mesh topology
1) Data can be transmitted from different
devices simultaneously. This topology can
withstand high traffic.
2) Even if one of the components fails there is
always an alternative present. So data transfer
doesn’t get affected.
3) Expansion and modification in topology can be
done without disrupting other nodes.
Disadvantages of Mesh topology
1) There are high chances of redundancy
in many of the network connections.
2) Overall cost of this network is way too
high as compared to other network
topologies.
3) Set-up and maintenance of this
topology is very difficult. Even
administration of the network is tough.
Hybrid Topology
 Combination
of
any two or more
network
topologies
› A hybrid topology
always accrues
when two
different basic
network
topologies are
connected
Advantages of Hybrid topology



One of the prominent advantages of this
topology is its flexibility. The topology is
designed, so that it can be implemented for a
number of different network environment.
As compared to most other topologies,
this topology is reliable. It has better fault
tolerance.
Any type of topology can be combined with
another without making any changes to the
existing topology
Disadvantages of Hybrid Topology
Since different topologies come together
in a hybrid topology, managing the
topology becomes difficult. It is also very
expensive to maintain.
 Installation and configuration of the
topology is difficult.

Communication

Main purpose of communication is to transfer information from a
source to a recipient via a channel or medium.

Basic block diagram of a communication system:
Source
Transmitter
Channel
Receiver
Recipient
Brief Description





Source: analog or digital
Transmitter: transducer, amplifier, modulator, oscillator, power
amp., antenna
Channel: e.g. cable, optical fibre, free space
Receiver: antenna, amplifier, demodulator, oscillator, power
amplifier, transducer
Recipient: e.g. person, (loud) speaker, computer
Data Communication Channels
or
Data Transmission Modes :
Simplex
 Half Duplex
 Full Duplex

Data Communication Channels
or
Data Transmission Modes
Simplex
◦ Data in a simplex channel is always one way. Simplex channels are not often used because
it is not possible to send back error or control signals to the transmit end. An example of
a simplex channel in a computer system is the interface between the keyboard and the
computer, in that key codes need only be sent one way from the keyboard to the
computer system.
 Half Duplex
◦ A half duplex channel can send and receive, but not at the same time. Its like a one-lane
bridge where two way traffic must give way in order to cross. Only one end transmits at a
time, the other end receives.
 Full Duplex
◦ Data can travel in both directions simultaneously. There is no need to switch from
transmit to receive mode like in half duplex. Its like a two lane bridge on a two-lane highway.


Analog and digital signals are used to
transmit information, usually through electric
signals. In both these technologies, the
information, such as any audio or video, is
transformed into electric signals.
The difference between analog and
digital technologies is that in analog
technology, information is translated into
electric pulses of varying amplitude. In digital
technology, translation of information is into
binary format (zero or one) where each bit
is representative of two distinct amplitudes.
Comparison chart




Analog
Analog signal is a
continuous signal
which represents
physical
measurements.
Denoted by sine waves
Uses continuous range
of values to represent
information



Digital
Digital signals are
discrete time signals
generated by digital
modulation.
Denoted by square
waves
Protocols
Network Protocol
Defines rules and conventions for communication between
network devices
 Protocols for computer networking all generally use packet
switching techniques to send and receive messages in the
form of packets
 Network protocols include mechanisms for:

› Devices to identify and make connections with each other
› Formatting rules that specify how data is packaged into
messages sent and received
› Message acknowledgement
› Data compression designed for reliable and/or highperformance network communication

Hundreds of different computer network protocols have
been developed each designed for specific purposes and
environments
What is OSI?




Developed by the International Organization for
Standardization (ISO) in 1984
The primary architectural model for intercomputer
communications.
A conceptual model composed of seven layers, each
specifying particular network functions.
Describes how information from a software application
in one computer moves through a network medium to
a software application in another computer.
OSI Lower Layers/OSI Upper Layers
Physical
2. Data Link
3. Network
1.
Transport
2. Session
3. Presentation
4. Application
1.
OSI Physical Layer
Responsible for transmission of bits
 Always implemented through hardware
 Encompasses mechanical, electrical, and
functional interfaces
 Transmission technique: determines
whether the encoded bits will be
transmitted by baseband (digital) or
broadband (analog) signaling.

OSI Data Link Layer







Link establishment and termination: establishes and
terminates the logical link between two nodes.
Frame traffic control: tells the transmitting node to "back-off"
when no frame buffers are available.
Frame sequencing: transmits/receives frames sequentially.
Frame acknowledgment: provides/expects frame
acknowledgments. Detects and recovers from errors that
occur in the physical layer by retransmitting nonacknowledged frames and handling duplicate frame receipt.
Frame delimiting: creates and recognizes frame boundaries.
Frame error checking: checks received frames for integrity.
Media access management: determines when the node "has
the right" to use the physical medium.
OSI Network Layer





Routing: routes frames among networks.
Subnet traffic control: routers (network layer intermediate
systems) can instruct a sending station to "throttle back" its
frame transmission when the router's buffer fills up.
Frame fragmentation: if it determines that a downstream
router's maximum transmission unit (MTU) size is less than
the frame size, a router can fragment a frame for
transmission and re-assembly at the destination station.
Logical-physical address mapping: translates logical addresses,
or names, into physical addresses.
Subnet usage accounting: has accounting functions to keep
track of frames forwarded by subnet intermediate systems,
to produce billing information.
OSI Transport Layer
Message segmentation: accepts a message from the
(session) layer above it, splits the message into
smaller units (if not already small enough), and passes
the smaller units down to the network layer. The
transport layer at the destination station reassembles
the message.
 Message acknowledgment: provides reliable end-toend message delivery with acknowledgments.
 Message traffic control: tells the transmitting station
to "back-off" when no message buffers are available.
 Session multiplexing: multiplexes several message
streams, or sessions onto one logical link and keeps
track of which messages belong to which sessions
(see session layer).

OSI Session Layer
Session establishment, maintenance and
termination: allows two application
processes on different machines to
establish, use and terminate a connection,
called a session.
 Session support: performs the functions
that allow these processes to
communicate over the network,
performing security, name recognition,
logging, and so on.

OSI Presentation Layer
Character code translation: for example,
ASCII to EBCDIC.
 Data conversion: bit order, CR-CR/LF,
integer-floating point, and so on.
 Data compression: reduces the number of
bits that need to be transmitted on the
network.
 Data encryption: encrypt data for security
purposes. For example, password
encryption.

OSI Application Layer
Resource sharing and device redirection
 Remote file access
 Remote printer access
 Inter-process communication
 Network management
 Directory services
 Electronic messaging (such as mail)
 Network virtual terminals

TCP/IP
Transmission control Protocol/Internet
Protocol
 Developed by DARPA
 No official protocol standard
 Can identify five layers

◦
◦
◦
◦
◦
Application
Host-to-Host (transport)
Internet
Network Access
Physical
An OSI View of TCP/IP
TCP\IP Model
OSI Model
Application
(http, telnet, snmp,
smtp, nfs, ftp)
Transport
(TCP, UDP)
Internet (IPv4/IPv6)
Network Access
Physical layer
(HDLC)
Sender
Application
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
HTTP
Request
TCP HTTP
Request
IP
TCP HTTP
Ethernet IP
Receiver
Application
Layer
Transport
Layer
Request
TCP HTTP
Request
Network
Layer
Data Link
Layer
Physical
Layer
HTTP
Request
TCP HTTP
Request
IP
TCP HTTP
Ethernet IP
Request
TCP HTTP
Request
TCP/IP Network Access Layer
Exchange of data between end system and
network
 Address of host and destination
 Prioritization of transmission
 Software at this layer depends on network

TCP/IP Internet Layer
An Internet is an interconnection of two or
more networks
 Internet layer handles tasks similar to network
access layer, but between networks rather than
between nodes on a network
 Uses IP for addressing and routing across
networks
 Implemented in workstations and routers

TCP/IP Transport Layer
Also called host-to-host layer
 Reliable exchange of data between
applications
 Uses TCP protocols for transmission

TCP/IP Application Layer
Logic needed to support variety of applications
 Separate module supports each type of
application (e.g. file transfer)

◦
◦
◦
◦
◦
FTP
HTTP
Telnet
News
SMTP
*TCP/IP
Application
Presentation
Session
Transport
TELNET
FTP
SMTP
DNS
SNMP
DHCP
RIP
RTP
RTCP
Transmission
Control Protocol
User Datagram
Protocol
OSPF
ICMP
IGMP
Internet Protocol
Network
ARP
Data link
Physical
Ethernet
Token Bus
Token Ring
FDDI
Overview of the Internet
Internet – a vast network of LANs and
WANs that electronically connects
millions of people worldwide
 The Internet was formed in 1969 by
ARPA, whose network, ARPANET,
featured multiple servers and connections

The World Wide Web
World Wide Web – a set of software
programs that enables users to access
resources on the Internet via hypertext
documents, or Web pages
 Web page – a document created in HTML
containing hypertext links that, when clicked,
enable users to access a different location or
document
 Web site – a collection of related Web pages
 Web browser – a software application that
enables users to easily access, view and
navigate Web pages on the Internet

How the Internet Works

Network protocols and packets:
◦ Protocol – an agreed-upon format for
transmitting data between two devices
◦ Packet – a fixed piece of information sent
across a network

Every computer connected to the
Internet uses Transmission Control
Protocol/Internet Protocol (TCP/IP)
◦ TCP/IP – software that makes Internet
communication possible
How the Internet Works (cont’d)

Computers access information from the
Internet as follows:
◦ You request data from an Internet server
◦ The request is divided into packets
◦ The packets are routed from your LAN to
the Internet backbone
◦ The packets are routed from the Internet
backbone to the destination server
◦ The destination server sends the requested
information using the same process
Connecting to the Internet

Six elements are required to connect to
the Internet:
◦
◦
◦
◦
◦
Computer
Operating system
TCP/IP
Client software
Internet connection (dial-up or direct through
an ISP)
◦ Internet address
Internet Service Providers (ISPs)

Internet Service Provider (ISP) – an
organization that provides access to the
Internet
◦ Most ISPs charge a flat monthly rate
◦ There are some basic-service ISPs that offer
Internet connectivity for free
◦ ISPs offer dial-up or direct Internet
connections
Internet Protocols

Internet Protocol version 4 (IPv4) –
supports 32-bit dotted quad IP address
format
◦ Most widely used version of IP
◦ Approximately 4 billion possible IP addresses

Internet Protocol version 6 (IPv6) –
supports
128-bit hexadecimal address format
◦ Also known as Internet Protocol Next
Generation (IPng)
◦ Will replace IPv4 in the future
◦ Approximately 4 trillion possible IP addresses
Internet Protocols (cont’d)




Hypertext Transfer Protocol (HTTP) – used
to transfer Web pages from a Web server to
a Web client (Web browser)
Hypertext Transfer Protocol Secure
(HTTPS) – used to access a secure Web
server
File Transfer Protocol (FTP) – used to
transfer files between computers on the
Internet
Electronic mail (e-mail) protocols:
◦ Simple Mail Transfer Protocol (SMTP) – used to transfer e-mail
messages to others with an outgoing mail server
Domain Name System (DNS)
Domain Name System (DNS) – resolves
IP addresses into easily recognizable
names
 For example:

◦ 64.128.206.9 = www.CIW-certified.com

Domain name and IP address refer to the
same Web server
Typical Domain Name
www.CIW-certified.com
Server (host)
name
Registered
company
domain name
Domain
category
(top-level
domain)
Top-Level Domains







com — commercial or company sites
edu — educational institutions, typically
universities
org — organizations; originally clubs,
associations and nonprofit groups; currently,
various types of organizations
mil — U.S. military
gov — U.S. civilian government
net — network sites, including ISPs
int — international organizations (rarely
used)
Applications /Services
Operations Of Internet
Download programs and files
 E-Mail
 Voice and Video Conferencing
 E-Commerce
 File Sharing
 Information browsing
 Search the web addresses for access through search
engine
 Chatting and many more…

Disadvantages of Internet




Theft of personal information such as name, address, credit card
number etc.
Virus threats nothing but a program which disrupts the normal
functioning of your system.
Spamming refers to receiving unwanted e-mails in bulk, which
provide no purpose and needlessly obstruct the entire system.
Pornography This is perhaps the biggest threat related to children’s
healthy mental life.A very serious issue concerning the Internet.
Though, internet can also create havoc, destruction and
its misuse can be very fatal,
the advantages of it outweigh its disadvantages.
What is Intranet ?

Internal company network that uses Internet standards
(HTML, HTTP & TCP/IP protocols) & software.

Accessed only by authorized persons, especially
members or employees of the organization
Applications of Intranet
Sharing of company policies/rules & regulations
 Access employee database
 Distribution of circulars/Office Orders
 Access product & customer data
 Sharing of information of common interest
 Launching of personal/departmental home pages
 Submission of reports
 Corporate telephone directories

Disadvantages
Management
problem
Security
problem

A company may not have person to update their
Intranet on a routine basis

Fear of sharing information and the loss of control

Limited bandwidth for the business

Unauthorized access
Abuse of access
Denial of service


Productivity
problem



Information overload lowers productivity
True purpose of the Intranet is unknown to many
employees/departments
Hidden or unknown complexity and costs
What is Extranet ?

Extranet is an Intranet for outside authorized users using
same internet technology.

Inter-organizational information system.

enable outsiders to work together with company’s
employees.

open to selected suppliers, customers & other business partners
Benefits of Extranet
Improved quality.
 lower travel costs.
 lower administrative & other overhead costs.
 reduction in paperwork.
 delivery of accurate information on time.
 improved customer service.
 better communication.
 overall improvement in business
effectiveness.

Disadvantages





The suppliers & customer who don’t
have technical knowledge feel problem.
Faceless contact.
Information can be misused by other competitors.
Fraud may be possible.
Technical Employees are required.
Communication Media

•
•
•
Cables
coaxial
twisted-pair
fiber optic

•
•
•
Wireless Media
Infrared
Narrowband radio
Microwave
Cables
pp.
Cable is used to connect network devices.
There are many types of networking cable in
use today. Different types of cable have
particular strengths and weaknesses, most
notably in the speed at which they can
transfer information.
111-116
Cables
The vast majority of networks are connected by
some sort of cabling. The cables are the network
transmission media that carry signals between
computers.
Three major groups of cabling connect the
majority of networks:
• coaxial
• twisted-pair
• fiber optic
pp.
111-116
Coaxial cable
Coaxial cable consists of
a core of copper wire
surrounded by insulation,
a
braided
metal
shielding, and an outer
cover.
pp.
111-116
shielding
A layer of
covering that grounds a
cable and protects it from
electric noise and crosstalk.
Twisted-Pair Cable
The twisting of the
twisted-pair cable wire
cancels out crosstalk from
adjacent pairs of cable.
The higher the number of
twists per foot of cable,
the more effectively it
cancels out crosstalk.
The total number of pairs
in
a
cable
varies,
depending on the purpose
of the cable.
pp.
111-116
twisted-pair cable A type of
cable that consists of two
insulated strands of copper
wire twisted around each
other.
Twisted Pair Cable
pp.
Fiber Optic Cable
In a fiber optic cable,
pulses of light travel down
extremely thin tubes of
glass or plastic to transmit
data.
The signal—a light
pulse—can be transmitted
over many miles very
quickly.
111-116
fiber optic cable A type of
cable made up of extremely
thin tubes of glass or plastic
that allow pulses of light to
travel through it to transmit
data.
Wireless Media
•Infrared
•Narrowband radio
•Microwave
pp.
125-128
Infrared Light
There are four types of
infrared networks:
• line-of-sight
• scatter infrared
• reflective
• broadband optical
telepoint
infrared A type of light
beam used in wireless
networks to transmit the data
between devices.
pp.
125-128
Narrowband Radio
Narrowband radio is
similar to broadcasting
from a radio station. The
broadcast range is 3,000
meters (9,842 feet), and
does not require line-ofsight focusing. However,
because the signal is high
frequency, it is subject to
attenuation from steel and
load-bearing walls.
narrowband radio
A high-frequency
transmission similar to
broadcasting from a radio
station. The user tunes both
the transmitter and the
receiver to a certain
frequency.
pp.
125-128
pp.
Microwave
Microwave systems can
be used for the following:
• satellite-to-ground links
• between two buildings
• across large, flat, and open
areas, such as bodies of
water or deserts
microwave
Part of the
electromagnetic
spectrum,
and a form of radiation that
can be used for short- and
long-distance
communications systems.
125-128
Microwave Technology
pp.
125-128
A microwave system can be used to transmit data from building to
building.
Network hardware
Cables
 Wireless Media
 Hubs
 Repeaters
 Bridges and Switches
 Routers
 Gateways
 Modems

Hubs
The hub is a central hardware component for many LANs. Hubs
operate at the Physical Layer in the OSI model. Hubs contain
multiple ports, and can connect to other hubs to expand the
network.
pp.
104-109
Repeaters
Repeaters operate at the
Physical Layer of the OSI
model. Essentially,
repeaters allow smaller
LANs to grow into larger
LANs by moving
transmissions from one
network segment to
another.
pp.
repeater A device that can
be used to connect two
cables and that boosts the
signal before sending it
along.
segment A section of the
network that includes the
cable and nodes that are
connected to a device, such
as a repeater, hub, or bridge.
104-109
Bridges and Switches
Bridges can be used to
connect dissimilar network
segments that use
different methods of
transferring data.
In today’s networks, it is
uncommon to find bridges
because switches
provide “multibridge”
capability.
bridge A device used to
connect two network
segments together.
switch A multiport bridge
that allows several segments
of a network to communicate
with one another.
pp.
104-109
Bridges and Switches
An important function of bridges and switches is to minimize
collision of data packets by creating collision domains. Bridges
and switches prevent the passing of collisions from one network
segment to another.
pp.
104-109
pp.
Routers
Bridges are clever
devices, but they are not
as smart as routers.
Brides forward data from
one network segment to
another, routers:
• forward packets from one
network to another and ,
• determine the best route to
use to deliver the data
router A network device
used to connect networks of
different types and that
forwards packets from one
network to another, even
those separated by great
distances. A router
determines the best route to
use to deliver the data.
104-109
pp.
Gateways
Gateways enable
dissimilar networks to
communicate. Gateways
operate at higher levels in
the OSI model such as
the Application,
Presentation, and Session
layers. In some cases,
they operate at all seven
layers.
gateway A dedicated
network computer whose job
is to convert data packets
from one network protocol to
another. Enables dissimilar
networks to communicate.
104-109
Modems

•
•
A modem is a computerto-computer
communication device
that converts digital
signals from the
computer to analog
signals for the telephone
lines. The word “modem”
comes from the two
operations it handles:
modulation
demodulation


modulation The
process on changing the
digital signal to an analog
signal on the sending
computer.
demodulation The
process of converting
the analog signal back to
a digital signal on the
receiving computer.
Queries??
Queries?