1. Lecture 5 Communications and Networks

2. Communications What is computer communications?
A process in which one computer transfers data, instructions, and information to another computer(s) a d c b e f

3. Uses of Communications Technologies
Voice mail
Fax
Chatroom
Instant Message
FTP
Newsgroup
Telephony
Videoconference
Groupware
Global Positioning System (GPS)

4. share data and information facilitate communications
Networks
share data and information
What is a network?
A collection of computers and devices connected by communications channels
Facilitates communications among users
Allows users to share resources
facilitate communications
share hardware
share software

5. Networks What is a local area network (LAN)?
Network that connects computers and devices in a limited geographical area.
Often uses Ethernet protocol

6. Networks What is a node ? Each computer or device on a network
What is a node ?
Each computer or device on a network
often the nodes are connected to the LAN via cables
node
node
a wireless LAN (WLAN) is a LAN that uses no physical wires
node
node
node

7. Networks What is a network operating system?
The system software that organizes and coordinates the activities on LAN
Also called a network OS or NOS
Administration
Adding, deleting, and organizing users and performing maintenance tasks
File management
Locating and transferring files
Printer management
Prioritizing print jobs and reports sent to specific printers on the network
Security
Monitoring and, when necessary, restricting access to network resources

8. Networks What are servers and clients? Server
file server stores and manages files
Server
Controls access to the hardware and software on the network
Provides a centralized storage are for programs
Dedicated servers perform a specific task
Clients
Other computers on the network
Rely on the server for resources
print server manages printers and print jobs
database server stores and provides access to a database
network server manages network traffic

9. Networks What is an Internet use of peer-to-peer (P2P)?
An Internet network that enables users with the same networking software to connect to each other’s hard disks and exchange files directly
Napster and Gnutella are two examples of P2P

10. Networks What is a network topology?
The configuration, or physical arrangement, of the devices in a communications network
Networks usually use combinations of three topologies
bus
ring
star

11. Networks What is a bus network?
Consists of a single central cable, to which all computers and other devices connect
The bus is the physical cable
The bus is also called the backbone
Inexpensive and easy to install
personal computer
personal computer
personal computer
personal computer
personal computer

12. Networks What is a ring network?
A cable forms a closed ring, or loop, with all computers and devices arranged along the ring
Data travels from device to device around the entire ring

13. Networks What is a star network?
All of the devices connect to a central computer/hub
All data that transfers from one computer to another passes through the hub
personal computer
personal computer
personal computer
host computer
personal computer
printer
file server

14. Networks What is an intranet?
has a Web server
What is an intranet?
An internal network that uses Internet technologies
Generally make company information accessible to employees and facilitate working in groups
Typically also includes a connection to the Internet
uses TCP/IP technologies
accessible via a Web browser
supports multimedia Web pages coded in HTML
users can post and update information on the intranet by creating and posting a Web page

15. Networks What is an extranet?
Allows customers or suppliers to access part of a company’s intranet

16. Networks What is a firewall?
Hardware and/or software that restricts access to data and information on a network
personal computer
printer
personal computer
corporate network
personal computer
Internet
firewall
personal computer
personal computer
personal computer
personal computer

17. Networks What is a home network?
Multiple computers connected together in a home or home office
All computers in the house can
connect to the Internet at the same time
Access files and programs on the other computers in the home
Share peripherals

18. Networks What is an intelligent home network?
Extends the basic home network to include features such as lighting control, thermostat adjustment, and a security system

19. Communications Software
What is communications software?
Consists of programs that help you establish a connection to another computer or network
Manages the transmission of data, instructions, and information

20. Costs no more than making a regular call
The Telephone Network
What is a dial-up line?
A temporary connection that uses one or more analog telephone lines for communications
A modem at the sending end dials the telephone number of a modem at the receiving end
Advantages
Costs no more than making a regular call
Computers at any two locations can establish a connection using modems and the telephone network
Disadvantage
Cannot control the quality of the connection because the telephone company’s switching office randomly selects the line

21. Can be analog or digital
The Telephone Network
What is a dedicated line?
A connection that always is established between two communications devices
The quality and consistency of the connection is better because dedicated lines provide a consistent connection
Can be analog or digital
Digital lines transfer data and information at faster rates than analog lines

22. The Telephone Network What is transfer rate?
The speed with which a line carries data and information
The faster the transfer rate the faster you can send and receive data and information
Usually are expressed as bits per second (bps)
bits per second (bps)
kilobits per second (Kbps)
megabits per second (Mbps)
gigabits per second (Gbps)

23. The Telephone Network
What are popular types of digital dedicated lines?
ISDN
DSL
T-carrier
CATV
ATM

24. Communications Devices
What is a communications device?
Any type of hardware capable of transmitting data, instructions, and information between a sending device and a receiving device
Sometimes the device must convert the data, instructions, and information from analog to digital signals or vice versa
cable modems
dial-up modems
ISDN and DSL modems
network interface cards

25. Communications Devices
What is a modem?
A communications device that converts a computer's digital signals to analog signals before they are transmitted over standard telephone lines
Sometimes called a dial-up modem
mo + dem
modulate
To change into an analog signal
demodulate
To convert an analog signal into a digital signal

26. Communications Devices
What is a digital modem?
One that sends and receives data and information to and from a digital telephone line such as ISDN or DSL
ISDN modem
Also called an ISDN adapter
Sends and receives digital data to an ISDN line
DSL modem
Sends and receives digital data to a DSL line

27. Communications Devices
What is a cable modem?
A modem that sends and receives data over the cable television (CATV) network
Currently much faster than a dial-up modem or ISDN
Usually attaches to a USB port or a port on a network interface card

28. Communications Devices
What is a network interface card (NIC)?
A card you insert into an expansion slot of a personal computer or other device, enabling the device to connect to a network
NIC for desktop computer
NIC for notebook computer

29. Communications Channel
What is a BUS?
The communications path between two devices

30. Physical Transmission Media
What is twisted-pair cable?
Consists of one or more twisted pair wires bundled together
Each twisted pair wire consists of two separate insulated copper wires
Twisted together to reduce noise
Noise is an electrical disturbance that can degrade communications
twisted pair cable
twisted pair cable
twisted pair wire

31. Physical Transmission Media
What is coaxial cable?
Consists of a single copper wire surrounded by at least three layers
Often called coax
Often used for cable television wiring
plastic outer coating
woven or braided wire
insulating material
copper wire
coaxial cable

32. Physical Transmission Media
What is fiber-optic cable?
Contains a core of dozens or hundreds of thin strands of glass or plastic
Uses light to transmit signals
Each strand is called an optical fiber
Thin as a human hair
protective coating
glass cladding
optical fiber core
cable contains many optical fibers
outer covering jacket
fiber-optic cable between floors of a building

33. Wireless Transmission Media
What is broadcast radio?
A wireless transmission medium that distributes radio signals through the air over long distances such as between cities, regions, and countries and short distances such as within an office or home
Slower and more susceptible to noise than physical transmission media
transmitter
sends the broadcast radio signal
receiver
accepts the broadcast radio signal
must have an antenna that is located in the range of the signal
transceiver
both sends and receives signals from wireless devices

34. Wireless Transmission Media
What is cellular radio?
A form of broadcast radio that is used widely for mobile communications, specifically wireless modems and cellular telephones
A cellular telephone is a telephone device that uses radio signals to transmit voice and digital data messages
mobile telephone switching office (MTSO)
calling party in auto
cell
public switched telephone network
cell
cell
base station (microwave station)
cell
called party

35. Wireless Transmission Media
What is a microwave station?
An earth-based reflective dish that contains the equipment necessary for microwave communications
Microwaves are extremely high-speed signals
Line-of-sight towers
Must transmit in a straight line

36. Wireless Transmission Media
What is a communications satellite?
A space station that receives microwave signals from an earth-based station, amplifies the signals, and broadcasts the signals back over a wide area to any number of earth-based stations
Transmission to a satellite is an uplink
Transmission from a satellite to an earth-based station is a downlink

37. Wireless Transmission Media
What is infrared (IR)?
A wireless transmission media that sends signals using infrared light waves
Requires a line-of-sight transmission
Many computers and devices have an IrDA port that enables the transfer of data using infrared light rays