1. Networks
Chapter 9

2. Objectives Describe the basic components of a network
Explain the methods of data transmission, including types of signals, modulation, and choices among transmission modes
Differentiate among the various kinds of communications links and appreciate the need for protocols
Describe various network configurations
List the components, types, and protocols of a local area network
Appreciate the complexity of networking
Describe some examples of networking
MIS105: Networks

3. Contents Data Communications Network Data Transmission
Communications Media
Network Topology
Local Area Network
Wide Area Network
Organization of Resources
Protocol
Software
Communication Applications
MIS105: Networks

4. Send and receive information over communications lines
Data Communications
Send and receive information over communications lines
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5. Centralized Data Processing
All processing, hardware, software in one central location
Inefficient
Inconvenient
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6. Distributed Data Processing
Computers at a distance from central computer
Can do some processing on their own
Can access the central computer
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7. Distributed Data Processing

8. Network
Uses communication equipment to connect two or more computers and their resources
PC based
LAN – shares data and resources among users in close proximity
WAN – shares data among users who are geographically distant
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9. Sending device Communications link Receiving device
Basic Components
Sending device Communications link Receiving device
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10. Network Design Data Transmission (Analog or Digital)
Media (Modem, Routers etc)
Topology – Physical layout of components
Protocol – Rules governing communication of data
Distance
LAN
WAN
Technology
Peer-to-peer
File server
Client/server
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11. Data Transmission Digital Transmission Sends data as distinct pulses
Data is represented as an
electromagnetic signal
Need digital line
Analog Transmission
Sends a continuous electrical signal in the form of a wave
Conversion from digital to analog needed
Telephone lines, coaxial cables, microwave circuits

12. Digital Transmission Asynchronous and Synchronous
Sending and receiving devices must work together to communicate
MIS105: Networks

13. Asynchronous Transmission
Contains start/stop bits
Start signal
Generally one character at a time (8 bits)
Stop signal
Low-speed communications

14. Synchronous Transmission
Blocks of data transmitted at a time
Send multiple characters at a time
Align internal clock of sending / receiving devices
Send error-check bits
More complex
More expensive
Faster transmission
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15. Analog Transmission
Data is transmitted through alteration of the carrier wave (a basic frequency)
Amplitude Modulation (AM) – height of the wave is increased to represent 1; higher amplitude means higher strength of sound or pixel
Frequency Modulation (FM) – number of times wave repeats during a specific time interval can be increased to represent a 1
Low cost
Good for shorter distance
Still very popular
MIS105: Networks

16. Modem Modem = Modulation + Demodulation Modulate Demodulate
Convert from digital to analog
Demodulate
Convert from analog to digital
Speeds up to 56,000 bps (56K)

17. Modem Transmission process
Modulation – Computer digital signals converted to analog
Sent over analog phone line
Demodulation – Analog signal converted back to digital

18. Types of Modems Direct-connect PCMCIA External Internal
Personal Computer Memory Card International Association
Notebook and laptop computers

19. Types of Modems DSL: Digital Subscriber Line
Uses conventional telephone lines
Uses multiple frequencies to simulate many modems transmitting at once
No industry standard
Cost
Speed (usually upto 3Mbps)
Phone line shared between computer and voice
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20. Types of Modems Cable Modem Coaxial cables
Does not interfere with cable TV reception
Up to 10 million bps
Always on
Shared capacity
Security problem
05: Networks

21. Types of Modems Cellular Modems Uses cellular telephone system
Slower speed
MIS105: Networks

22. ISDN Integrated Services Digital Network
One of the oldest Digital broadband transmission
Speeds upto 128 Kbps
Connect and talk at the same time
Need
Adapter
Upgraded phone service
Initial costs high
Ongoing monthly fees may be high
Not available in all areas
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23. Types of Communication Channels
Direction of data flow
Simplex
One direction
Television broadcasting
Arrival/departure screens at airport
Half-duplex
Either direction, but one way at a time
CB radio
Bank deposit sent, confirmation received
Full-duplex
Both directions at once
Telephone conversation
Point to Point (P2P or Pt2Pt)
Connection restricted to 2 endpoints
Eg, 2 computers connected directly using their interface cards
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24. Communications Media Physical means of transmission Bandwidth
Range of frequencies that the medium can carry
Measure of capacity
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25. Network Cable Twisted pair Coaxial cable Fiber optic cable Wireless
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26. Twisted Pair Cable Inexpensive
Susceptible to electrical interference (noise)
Telephone systems
Physical characteristics
Requires two conductors
Twisted around each other to reduce electrical interference
Plastic sheath
Shielded twisted pair
Metallic protective sheath
Reduces noise
Increases speed
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27. Coaxial Cable Higher bandwidth Less susceptible to noise
Used in cable TV systems
Physical characteristics
Center conductor wire
Surrounded by a layer of insulation
Surrounded by a braided outer conductor
Encased in a protective sheath
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28. Fiber Optics Transmits using light Higher bandwidth Less expensive
Immune to electrical noise
More secure – easy to notice an attempt to intercept signal
Physical characterizes
Glass or plastic fibers
Very thin
Material is light
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29. Wireless Transmission
Uses infrared or low-power radio wave transmissions
No cables
Easy to set up and reconfigure
Slower transmission rates
Small distance between nodes
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30. Microwave Transmission
Line-of-site
High speed
Cost effective
Easy to implement
Weather can cause interference
Physical characteristics
Data signals sent through atmosphere
Signals cannot bend of follow curvature of earth
Relay stations required
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31. Satellite Transmission
Microwave transmission with a satellite acting as a relay
Long distance
Components
Earth stations – send and receive signals
Transponder – satellite
Receives signal from earth station (uplink)
Amplifies signal
Changes the frequency
Retransmits the data to a receiving earth station (downlink)

32. Satellite Transmission

33. Network Topology Physical layout
Star
Ring
Bus
Node – any device connected to the network
Server
Computer
Printer
Other peripheral
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34. Network Topologies Packets Pieces of data transmitted over a network
Packets are created by sending node
Data is reassembled by receiving node
Packet header
Sending and receiving address
Packet payload
Number and size of data
Actual data
Packet error control
Teaching tip
For technical students take the time to draw the packet structure on the board. The typical structure is destination address | sending address | packet number | total packets | data size | payload | error control.
MIS105: Network Basics

35. Network Topologies Star topology All nodes connect to a hub Advantages
Packets sent to hub
Hub sends packet to destination
Advantages
Easy to setup
One cable can not crash network
Disadvantages
One hub crashing downs entire network
Uses lots of cable
Most common topology
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36. Star Topology
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37. Network Topologies Ring topology Nodes connected in a circle
Tokens used to transmit data
Nodes must wait for token to send
Advantages
Time to send data is known
No data collisions
Disadvantages
Slow
Lots of cable
One node can crash the entire network
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38. Network Topologies
Ring topology
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39. Token Ring Ring topology No danger from collisions Token passing
Token has an address
Node looks at token as it passes
Addressed to me? Retrieve data
Pass it on if not my address
Send
Empty token? Attach message
Pass it on if not empty
MIS105: Networks

40. Network Topologies Bus topology Also called linear bus
One wire connects all nodes
Terminator ends the wires
Advantages
Easy to setup
Small amount of wire
Disadvantages
Slow
Easy to crash
Teaching tip
Pages 352 and 353 have diagrams of each network topology
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41. Network Topologies
Bus topology
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42. Network Topologies Mesh topology All computers connected together
Internet is a mesh network
Advantage
Data will always be delivered
Disadvantages
Lots of cable
Hard to setup
rk Basics

43. Network Hardware Hubs Center of a star network
All nodes receive transmitted packets
Slow and insecure
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44. Network Hardware Switches Replacement for hubs
Only intended node receives transmission
Fast and secure
Insider information
Twisted pair networks cannot achieve higher than 10 Mbps using a hub. Switches are necessary to achieve 100 Mbps or higher.
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45. Network Hardware Bridge Connects two or more LANs together
Packets sent to remote LAN cross
Other packets do not cross
Segments the network on MAC addresses
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46. Network Hardware Router Connects two or more LANs together
Packets sent to remote LAN cross
Network is segmented by IP address
Connect internal networks to the Internet
Need configured before installation
Discussion point
Ask who in the class has high speed Internet. Then determine if anyone is sharing this to the rest of the house or dorm. If they are, see if they can describe the setup. Most likely, the sharing is done with a router.
MIS105: Network Basics

47. Network Hardware Gateway Connects two dissimilar networks
Connects coax to twisted pair
Most gateways contained in other devices
Gateway
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48. Connections over short distances through communications media
LAN Local Area Network
Components
PCs
Network cable
NIC
Connections over short distances through communications media
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49. LAN Network Interface Card (NIC)
Connects computer to the wiring in the network
Circuitry to handle
Sending
Receiving
Error checking
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50. WAN Wide Area Network
Link computers in geographically distant locations

51. Hybrid Network Types Campus Area Networks (CAN)
A LAN in one large geographic area
Resources related to the same organization
Each department shares the LAN
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52. Hybrid Network Types Metropolitan Area Network (MAN)
Large network that connects different organizations
Shares regional resources
A network provider sells time
Teaching tip
An example of a regional resource is a supercomputer. For example, Pittsburgh has the Pittsburgh Super Computing center ( The various colleges in Pittsburgh connect to the center through a MAN in Pittsburgh.
MIS105: Network Basics

53. Hybrid Network Types Home Area Network (HAN) Small scale network
Connects computers and entertainment appliances
Found mainly in the home
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54. Hybrid Network Types Personal Area Network (PAN)
Very small scale network
Range is less than 2 meters
Cell phones, PDAs, MP3 players
Insider information
PAN is very new. Few devices support PAN. High end cell phones include Bluetooth technology. Once the technology matures, Bluetooth will allow the creation of a PAN.
MIS105: Network Basics

55. Communication Services
Common carriers licensed by FCC (Federal Communications Commission)
Switched / dial-up service
Temporary connection between 2 points
Ex: plain old telephone service (POTS)
Dedicated service
Permanent connection between 2 or more locations
Ex: Build own circuits, Lease circuits (leased lines)
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56. High Capacity Digital Lines
1.54 Mbps
24 simultaneous voice connections T3
28 T1 lines
43 Mbps
Expensive
High-volume traffic
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57. Multiplexer
Combines data streams from slow-speed devices into single data stream
Transmits over high-speed circuit (ex T1)
Multiplexer on receiving end needed to restore to component data streams
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58. Organization of Resources Client/Server
Controls the network
Hard disk holding shared files
Clients
Other computers on network
Thin client – no processing
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59. Organization of Resources Client/Server and File Server
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60. Organization of Resources File Server
Server transmits file to client Client does own processing
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61. Organization of Resources Client/Server
How it works
Client sends request for service to server
Server fulfills request and send results to client
Client and server may share processing
Benefits
Reduces volume of data traffic
Allows faster response for each client
Nodes can be less expensive computers
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62. Organization of Resources Peer-to-Peer (P2P)
Peer to peer networks (P2PN)
All nodes are equal
Nodes access resources on other nodes
Each node controls its own resources
Most modern OS allow P2PN
Distributing computing is a form
Kazaa
Common with up to 12 computers
Disadvantage – slow transmission
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63. Organization of Resources Hybrid
Contains elements of various organizations to optimize transmission speed and organizational needs
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64. Protocol Set of rules governing the exchange of data
Assists with coordination of communications; ie, was the message received properly?
TCP/IP
Transmission Control Protocol / Internet Protocol
Internet standard
All computers in world speak same language
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65. Carrier sense multiple access with collision detection
Ethernet
CSMA/CD
Carrier sense multiple access with collision detection
Tries to avoid 2 or more computers communicating at the same time
Computer listens and transmits when cable is not in use
Collision results in waiting a random period and transmitting again
Performance degrades with multiple collisions
Dominant protocol
Bus or star topology
Uses CSMA/CD
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66. File Transfer Software
Download
Receive a file from another computer
Upload
Send a file to another computer

67. Terminal Emulation Software
PC imitates a terminal for communication to mainframe
Micro-to-mainframe link
MIS105: Networks

68. Office Automation Communication Applications
Facsimile (Fax)
Groupware
Teleconferencing
Video conferencing
ATM
Electronic fund transfers
Telecommuting
Online services
The Internet
Electronic data interchange (EDI)
MIS105: Networks