Communications and
Networks
Reading: Chapter 9
1
Why are networks so useful?
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They facilitate
communications
They allow for
sharing of resources
Both of the above
Th
1.
33% 33% 33%
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Network

Uses of communications technologies




Internet
Global Positioning System (GPS)
Short Message Service (SMS)
Network
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

Interconnected group of computers and devices connected via
communications devices and media
Facilitates sharing of resources and supports communications
Requires
 Sending & receiving devices
 Communications devices
 Communications channel or path
 Network OS (NOS)
3
Networks –
Communications Devices
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Communications Device
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Hardware capable of sending/receiving data
Convert signals so that they are suitable for the
communications channel

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May convert between analog and digital
Common types
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Dial-up modems
ISDN and DSL modems
Cable modems
Network interface cards
Wireless access points
Routers
4
Networks –
Communications Devices

Dial-up Modem
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Modulate/demodulate
External modem
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Internal modem
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Connects to serial or RS-232 port
Card inserted to expansion slot/PC Slot
ISDN and DSL Modems
Do not modulate/demodulate
External
Sends and receives data over a digital
telephone line
ISDN line
DSL line
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Networks –
Communications Devices

Cable modem
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Cable television network
Faster than dial-up access or ISDN line
Splitter runs separate cables to TV’s and cable modem
External
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USB port or Ethernet NIC via a cable
Network Interface Card (NIC)
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Coordinates transmission/receipt of data to/from the device
Card installed in an expansion slot of a PC, printer, PC slot
Wireless transmission includes antenna
Works with a particular network technology

Ethernet or token ring
6
Networks –
Communications Devices

Hub
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Router
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Connects multiple
computers and
routers together
Transmits packets to
correct destination
May include built-in
firewall


Provides a central
point of connectivity
for cables in a network
May include a router
Wireless access point


Allows computers and
devices to
communicate wirelessly
Allows data transfer to
a wired network
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Communications devices include
______.
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2.
routers
hubs
modems
NICs
All of the above
20% 20% 20% 20% 20%
ro
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1.
45
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Networks –
Communications Channels

Channel


Communications path between two devices
Transmission rate


Speed at which data flows through the channel
Bandwidth of the channel
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Bits per second (bps), Hertz (cycles per second)
Transmission media

Materials or techniques capable of carrying one or more signals

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Physical transmission media
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Baseband media – carry one signal at a time
Broadband media – carry multiple signals concurrently
Twisted pair, Coaxial, Fiber Optic
Wireless transmission media

Infrared, Radio Frequency, Infrared, Microwave
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Networks –
Physical Transmission Media

Twisted-pair cable
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
Used for network cabling and
telephone systems
One or more twisted-pair wires
bundled together

Each pair has two insulated copper
wires twisted together

Coaxial cable (coax)
Used for network cabling and cable
TV
Single copper wire surrounded by 3
layers

Insulating material
Woven/braided metal
Plastic outer coating

10
Networks –
Physical Transmission Media

Fiber optic cable


Light used to send signals
Thin glass or plastic strands






Surrounded by insulating
glass cladding and a
protective coating
Carries many signals
High speed
Less noise
Smaller size
Expensive, difficult to install
and modify
optical
fiber
core
glass
cladding
Protective coating
11
Networks –
Physical Transmission Media
12
All of the following except ______
are examples of physical media.
25% 25% 25% 25%
45
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3.
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2.
coaxial cable
twisted pair
microwave cable
fiber optic cable
co
1.
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Networks –
Wireless Transmission Media

Radio Frequency
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Antenna, transmitter,
receiver
Bluetooth (2.45 GHz)
802.11b & g (2.4 GHz)
Cellular Radio Waves
 Cell phones, mobile
devices
 High frequency radio
waves
 824 to 849 MHz

Infrared Signals


Microwaves
High-speed signal transmission
Signals sent between microwave
stations
Fixed-point wireless
Requires line-of-sight
Communications Satellites

Satellite receives microwave
signal and amplifies
Retransmits over wide-area, to
a number of land-based stations

IR light waves with line-of-sight transmission
14
Networks –
Wireless Transmission Media
15
All of the following except ______ are
examples of wireless media.
25% 25% 25% 25%
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3.
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w
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2.
microwaves
satellites
radio frequency
waves
fiber optic waves
m
ic
1.
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Networks

Classified according to

Geography – Geographic Distribution

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LAN
MAN
WAN
Architecture
Topology
Protocol/Communications Technology
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Networks –
Geographic Distribution
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Local Area Network (LAN)
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
Connects computers in a limited
geographical area
Each computer and device is a
node

Metropolitan Area Network (MAN)
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
High-speed network that connects LANs in
a metropolitan area
Managed by a consortium of users or a
single network provider
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Networks –
Geographic Distribution
Wide Area Network (WAN)
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Connects computers and devices in a large
geographical area

Connected via many types of media
One large network or two or more
interconnected LANs, MANs
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
Others
CAN
HAN
TAN

19
A ______ is a network that encompasses a
limited geographic area.
45
25%
25%
PA
N
LA
N
N
4.
W
A
3.
N
2.
25%
MAN
WAN
LAN
PAN
M
A
1.
25%
20
Networks

Classified according to

Geography
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Architecture – Broad outline of the network
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Peer-to-Peer
Client/Server
Topology
Protocol/Communications Technology
21
Network Architectures –
Client/Server and Peer-to-Peer
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Client/Server

client
client
Server controls resources

More storage space, power



client
Serves as a repository
Dedicated servers
Client relies on the server for
access to resources
printer

server
Peer-to-Peer
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Share peripheral devices
Up to 10 “peer” computers
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Internet Peer-to-Peer (P2P)
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NOS & applications software, storage
Users connect directly to each other’s
hard disk
Popular, inexpensive
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Networks
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Can be classified according to

Geography
Architecture
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Topology – Physical arrangement of devices

connected to the network
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Bus
Ring
Star

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Networks often use a combination of topologies
Protocol/Communications Technology
23
Network Topologies –
Bus and Ring Networks
 Bus Network
Single central cable connects computers and
devices
 Transmits in both directions
 If a device fails, network continues to function
Reliable
 Popular, inexpensive
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Ring Network
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Cable forms a closed ring
Transmits in only one direction
If one device fails, all those after the
device cannot function
Spans larger distance than bus network
LANs and WANs
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Network Topologies –
Star and Other Networks
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Star Network
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Devices connect to a central
computer

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If one device fails, only that
device is affected

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Hub
Hub fails
Other Topologies

Mesh

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Redundant interconnections between nodes
Tree

Star networks connected together via a bus
25
With ______ topology, the devices on the
network are connected together in a
closed loop.
25%
45
25%
tr
ee
St
ar
in
g
4.
R
3.
us
2.
25%
bus
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star
tree
B
1.
25%
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Networks

Can be classified according to

Geography
Architecture
Topology

Protocol/Communications Technology –

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Standards that govern how data/instructions flow over
the network
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Ethernet
Token Ring
TCP/IP
WAP
Others
27
Networks –
Network Communications Technologies
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Communications Protocol
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Set of rules and procedures for exchanging
information among computers
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Ethernet
Token ring
TCP/IP
WAP
Others
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Network Communications Technologies –
Ethernet
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Ethernet
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Widely used LAN standard
Developed by Xerox, DEC, Intel - 1976
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Fast Ethernet (100Base-T) - 100 Mbps
Gigabit Ethernet - 1000 Mbps
10-Gigabit Ethernet – 10 Gbps
Bus or star topology
PCs in the network to contend for access

Collision
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Network Communications Technologies –
Token Ring
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Token Ring
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Ring or star topology
LAN standard
Passes a signal called a token

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
Special bit pattern
Only device with token can transmit
Device catches the token, attaches message , sends it to
travel around the network to receiving device
Receiving device catches token, strips off the message,
resends token
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Network Communications Technologies –
TCP/IP

TCP/IP
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Used to connect hosts on the Internet
Includes several protocols
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Data broken up into small packets
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Transmission Control Protocol and Internet Protocol
Origin information
Destination information
Sequence information
Data/information/instructions
Packet switching
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
Break up message into packets, route packets, destination
reassembles the message
Routers direct packets individually along fastest path
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Network Communications Technologies –
WAP

Wireless Application Protocol
(WAP)

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Access Internet via mobile devices
2.0 Specification
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
Open Mobile Alliance (OMA)
Web sites provide wireless content
to display on microbrowsers

WML – XML application designed for
small screens
32
Network Communications Technologies –
802.11, Bluetooth, IrDA

IEEE 802.11 (802.11b, g – “WiFi”)

Family of standards used with wireless LANs

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Bluetooth


Devices contain special chip
Short-range radio waves transmit between Bluetooth devices

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Used for public Internet access points
Short distance
IrDA

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
IrDA devices contain IrDA ports
Infrared light waves
Line-of-sight transmission
33
With TCP/IP is used to send data over the
Internet, the data is divided into small
pieces or ______.
25%
45
25%
bs
hu
to
k
en
s
s
ck
et
4.
pa
3.
nd
le
s
2.
25%
bundles
packets
tokens
hubs
bu
1.
25%
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Networks –
Intranets

Intranet

Internal network in an organization used to share
information



Enterprise network
Connects to the Internet


Uses Internet technologies (TCP/IP, Web server, Web pages)
Extranet - Allows outside user access
Firewall

Designed to prevent unauthorized access to a private network



Firewall blocks messages that do not meet security criteria
Uses hardware, software, combination of both
All messages entering or leaving the intranet must pass through
the firewall
35
Networks –
Home Area Networks (HAN)

Network within a home

Connects digital devices
HomePLC – electrical lines; cables
connect card/USB/parallel port to wall
outlet
Phoneline – telephone lines; cables
connect NIC/PC card to telephone jack

Network card that plugs into
PCI slot and wall outlet for
home power-line network
Howstuffworks.com
HomeRF, 802.11b – radio waves; NIC connects to transceiver with
antenna or to wireless access point
Ethernet – twisted pair cables; Ethernet NIC cards and cables to
connect devices

36
Do you have a home area
network?
o
50%
N
s
2.
Yes
No
50%
Ye
1.
30
37
Networks Summary


Uses of Communications Technology
Networks


Communications Devices
Communications Channels


Geographic



Bus, Ring, Star
Protocols


Peer-to-Peer, Client/Server
Topologies


LAN, MAN, WAN
Architectures


Physical and Wireless Transmission Media
Ethernet, Token Ring, TCP/IP, WAP, 802.11, others
Intranets and Firewalls
Home Networks
38