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Networking- Computer Connections
Chapter 7
Data Communications
 Send and receive
information over
communications lines
 Centralized Data
Processing
 All processing,
hardware, software in
one central location
 Inefficient
 Inconvenient
Distributed Data Processing
 Computers at a
distance from
central
computer
 Can do some
processing on
their own
 Can access the
central
computer
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
 Basic Components
 Sending device
 Communications link
 Receiving device
Network Design
 Transmission Media
 Topology – Physical layout of components
 Protocol – Rules governing communication
 Distance/proximity
 LAN, CAN, MAN, WAN
 Technology
 Peer-to-peer
 File server
 Client/server
Data Transmission
 Digital lines
 Sends data as distinct pulses
 Need digital line
 Analog lines
 Sends a continuous electrical signal in the form
of a wave
 Conversion from digital to analog needed
 Telephone lines, coaxial cables, microwave
circuits
Analog Transmission
 Alter the carrier wave
 Amplitude – height of
the wave is increased
to represent 1
 Frequency – number
of times wave repeats
during a specific time
interval can be
increased to represent
a 1
Modem- Data Transmission
• Analog signal
converted back
to digital
Demodulation
• Sent over analog
phone line
Transmission
• Computer digital
signals converted
to analog
Modulation
Digital Transmission Lines
 Cable Modem
 Coaxial cables/ Dish TV
 Does not interfere with cable TV reception
 Up to 100 Mbps
 Always on, Shared capacity, Security?
 Integrated Services for Digital Network (ISDN)
 A set of communication standards/protocols for simultaneous digital
transmission of voice, video, data, and other network services
 ISDN is today primarily used for voice and fax traffic
 DSL- Digital Subscriber Line
 Uses conventional telephone lines
 Uses multiple frequencies/many transmitting at once
 No industry standard
 Phone line shared between computer and voice
 Cellular Modems
Speed
Cost
Convenience
Compatibility
Transmission using clock
 Asynchronous
 Start/stop transmission
 Start signal
 Group – generally one character
 Stop signal
 Less speed, less traffic
 Synchronous
 Blocks of data transmitted at a time
 Send bit pattern
 Align internal clock of sending / receiving devices
 Send data
 Send error-check bits
 More complex, expensive, speed
Asynchronous and Synchronous
Sending and
receiving devices
must work together
to communicate
Dedicated
Clock for
data
transmission!
Direction of data flow- Duplex Setting
 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
Communications Media
 Physical means of transmission
 Bandwidth
 Range of frequencies that the medium can carry
 Measure of capacity
Cables
 Wired
 Twisted pair
 Coaxial cable
 Fiber optic cable
 Wireless
 Uses infrared or low-power radio wave transmissions
 No cables
 Easy to set up and reconfigure
 Slower transmission rates
 Small distance between nodes
Twisted Pair- Wire Pair
 Considerations
 Inexpensive
 Susceptible to electrical interference (noise)
 Example- Telephone systems
 Shielded twisted pair
 Metallic protective sheath
 Reduces noise
 Increases speed
 Physical characteristics
 Requires two conductors
 Twisted around each other to reduce electrical interference
 Plastic sheath
Coaxial Cable
 Higher bandwidth
 Less susceptible to noise
 Used in cable TC systems
 Physical characteristics
 Center conductor wire
 Surrounded by a layer of insulation
 Surrounded by a braided outer conductor
 Encased in a protective sheath
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 (thinner than human hair)
 Material is light
Microwave Transmission
 Consideration
 High frequency is larger data capacity
 Line-of-site ~ shorter distance
 Cost effective
 Easy to implement
 Weather can cause interference
 microwave relay
 Physical characteristics
 Roughly 1-30 GHz ~ 30 cm-1.0 cm
 Data signals sent through atmosphere
 Signals cannot bend of follow curvature of earth
 Relay stations required
Satellite Transmission as a Microwave Relay
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)
Dhaka to Luxemburg
 Request made
 Twisted pair in the phone lines on the East Coast
 Microwave and satellite transmission across the
country
 Twisted pair in the phone lines on the West coast
 Data transferred
 Twisted pair in the phone lines on the West Coast
 Microwave and satellite transmission across the
country
 Twisted pair in the phone lines on the East coast
Network Topology
Physical layout- Star, Ring, Bus
…
Node – any device connected to the
network (topology). E.g. Server, Computer,
Printer, Other peripheral
Network Topology
Star
Central hub
All messages routed through hub
Hub prevents collisions
Node failure – no effect on overall
network
Hub failure – network fails
Ring
Travel around circular connection
in one direction
Node looks at data as it passes
• Addressed to me?
• Pass it on if not my address
No danger from collisions
Node failure – network fails
Bus
Single pathway
All nodes attached to single line
Collisions result in re-send
Node failure – no effect on overall
network
LAN- Local Area Network
 Consideration
 Connections over short distances
 Low Cost- equipment, maintenance
 Easy setup
 Components
 PCs
 Network cable
 NIC
 Connects computer to the wiring in the network
 Circuitry to handle Sending, Receiving, Error checking
Connecting Networks- LANs
 Hubs
 Bridge – connects networks with similar
protocols
 Switch (IP switches)
 Replacing routers
 Less expensive
 Faster
 Router – directs traffic via best path
 Gateway
 Connects LANs with dissimilar protocols
 Performs protocol conversion
Bridged Network Ring
WAN- Wide Area Network
 Link computers in geographically distant
locations
Communication Service Provider
 Common carriers licensed
 by FCC in the US
 Bangladesh Telecommunication Regulatory
Commission (BTRC)
 Bangladesh Telegraph and Telephone Board (BTTB)
 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)
High Capacity Digital Lines
 T1 digital transmission system (American)
 a single physical wire pair can be used to carry many
simultaneous voice conversations by time-division
multiplexing
 connect major telephone exchanges
 1.54 Mbps ~ 24 simultaneous voice connections
 T3 is 28 T1 lines = 43 Mbps
 Expensive, High-volume traffic
 E2 digital transmission system (European)
 E2: multiplexing level 2: 8 Mbit/s
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
Client/Server- e.g. a file server
Clients
Other computers on network
Thin client – no processing
Server
Controls the network
Hard disk holding shared files
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
 File Server System
 Server does authentication and transmits file to client
 Client does own processing
 Benefits
 Reduces volume of data traffic
 Allows faster response for each client
 Nodes can be less expensive computers
Organization of Resources
Peer-to-Peer Technology
 All computers have equal status
 Share data and devices as needed
 Disadvantage – slow transmission
Hybrid- Contains
elements of
various
organizations to
optimize
transmission speed
and organizational
needs
Protocol
 Set of rules governing the exchange of data
 Assists with coordination of communications
 Was message received properly?
 TCP/IP- Internet standard
 Transmission Control Protocol / Internet Protocol
 All computers in world speak same language
Protocol …
Ethernet
 Dominant protocol
 Bus or star topology
 Uses 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
Ring topology- Token Ring
 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
Application of the network
 File Transfer Software
 Download- Receive a file from another computer
 Upload- Send a file to another computer
 Terminal Emulation Software
 PC imitates a terminal for communication to
mainframe
 Micro-to-mainframe link
Office Automation
Communication Applications
 E-mail
 Facsimile (Fax)
 Groupware
 Teleconferencing
 Video conferencing
 ATM
 Electronic fund
transfers
 Telecommuting
 Online services
 The Internet
 Electronic data
interchange (EDI)
!@#$%^&*
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
Contents
 Data Communications
 Network
 Data Transmission
 Communications Media
 Network Topology
 Local Area Network
 Wide Area Network
 Organization of Resources
 Protocol
 Software
 Communication Applications

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Computer Networking Basics

  • 2. Data Communications  Send and receive information over communications lines  Centralized Data Processing  All processing, hardware, software in one central location  Inefficient  Inconvenient
  • 3. Distributed Data Processing  Computers at a distance from central computer  Can do some processing on their own  Can access the central computer
  • 4. 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  Basic Components  Sending device  Communications link  Receiving device
  • 5. Network Design  Transmission Media  Topology – Physical layout of components  Protocol – Rules governing communication  Distance/proximity  LAN, CAN, MAN, WAN  Technology  Peer-to-peer  File server  Client/server
  • 6. Data Transmission  Digital lines  Sends data as distinct pulses  Need digital line  Analog lines  Sends a continuous electrical signal in the form of a wave  Conversion from digital to analog needed  Telephone lines, coaxial cables, microwave circuits
  • 7. Analog Transmission  Alter the carrier wave  Amplitude – height of the wave is increased to represent 1  Frequency – number of times wave repeats during a specific time interval can be increased to represent a 1
  • 8. Modem- Data Transmission • Analog signal converted back to digital Demodulation • Sent over analog phone line Transmission • Computer digital signals converted to analog Modulation
  • 9. Digital Transmission Lines  Cable Modem  Coaxial cables/ Dish TV  Does not interfere with cable TV reception  Up to 100 Mbps  Always on, Shared capacity, Security?  Integrated Services for Digital Network (ISDN)  A set of communication standards/protocols for simultaneous digital transmission of voice, video, data, and other network services  ISDN is today primarily used for voice and fax traffic  DSL- Digital Subscriber Line  Uses conventional telephone lines  Uses multiple frequencies/many transmitting at once  No industry standard  Phone line shared between computer and voice  Cellular Modems Speed Cost Convenience Compatibility
  • 10. Transmission using clock  Asynchronous  Start/stop transmission  Start signal  Group – generally one character  Stop signal  Less speed, less traffic  Synchronous  Blocks of data transmitted at a time  Send bit pattern  Align internal clock of sending / receiving devices  Send data  Send error-check bits  More complex, expensive, speed
  • 11. Asynchronous and Synchronous Sending and receiving devices must work together to communicate Dedicated Clock for data transmission!
  • 12. Direction of data flow- Duplex Setting  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
  • 13. Communications Media  Physical means of transmission  Bandwidth  Range of frequencies that the medium can carry  Measure of capacity
  • 14. Cables  Wired  Twisted pair  Coaxial cable  Fiber optic cable  Wireless  Uses infrared or low-power radio wave transmissions  No cables  Easy to set up and reconfigure  Slower transmission rates  Small distance between nodes
  • 15. Twisted Pair- Wire Pair  Considerations  Inexpensive  Susceptible to electrical interference (noise)  Example- Telephone systems  Shielded twisted pair  Metallic protective sheath  Reduces noise  Increases speed  Physical characteristics  Requires two conductors  Twisted around each other to reduce electrical interference  Plastic sheath
  • 16. Coaxial Cable  Higher bandwidth  Less susceptible to noise  Used in cable TC systems  Physical characteristics  Center conductor wire  Surrounded by a layer of insulation  Surrounded by a braided outer conductor  Encased in a protective sheath
  • 17. 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 (thinner than human hair)  Material is light
  • 18. Microwave Transmission  Consideration  High frequency is larger data capacity  Line-of-site ~ shorter distance  Cost effective  Easy to implement  Weather can cause interference  microwave relay  Physical characteristics  Roughly 1-30 GHz ~ 30 cm-1.0 cm  Data signals sent through atmosphere  Signals cannot bend of follow curvature of earth  Relay stations required
  • 19. Satellite Transmission as a Microwave Relay
  • 20. 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)
  • 21. Dhaka to Luxemburg  Request made  Twisted pair in the phone lines on the East Coast  Microwave and satellite transmission across the country  Twisted pair in the phone lines on the West coast  Data transferred  Twisted pair in the phone lines on the West Coast  Microwave and satellite transmission across the country  Twisted pair in the phone lines on the East coast
  • 22. Network Topology Physical layout- Star, Ring, Bus … Node – any device connected to the network (topology). E.g. Server, Computer, Printer, Other peripheral
  • 23. Network Topology Star Central hub All messages routed through hub Hub prevents collisions Node failure – no effect on overall network Hub failure – network fails Ring Travel around circular connection in one direction Node looks at data as it passes • Addressed to me? • Pass it on if not my address No danger from collisions Node failure – network fails Bus Single pathway All nodes attached to single line Collisions result in re-send Node failure – no effect on overall network
  • 24. LAN- Local Area Network  Consideration  Connections over short distances  Low Cost- equipment, maintenance  Easy setup  Components  PCs  Network cable  NIC  Connects computer to the wiring in the network  Circuitry to handle Sending, Receiving, Error checking
  • 25. Connecting Networks- LANs  Hubs  Bridge – connects networks with similar protocols  Switch (IP switches)  Replacing routers  Less expensive  Faster  Router – directs traffic via best path  Gateway  Connects LANs with dissimilar protocols  Performs protocol conversion
  • 27. WAN- Wide Area Network  Link computers in geographically distant locations
  • 28. Communication Service Provider  Common carriers licensed  by FCC in the US  Bangladesh Telecommunication Regulatory Commission (BTRC)  Bangladesh Telegraph and Telephone Board (BTTB)  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)
  • 29. High Capacity Digital Lines  T1 digital transmission system (American)  a single physical wire pair can be used to carry many simultaneous voice conversations by time-division multiplexing  connect major telephone exchanges  1.54 Mbps ~ 24 simultaneous voice connections  T3 is 28 T1 lines = 43 Mbps  Expensive, High-volume traffic  E2 digital transmission system (European)  E2: multiplexing level 2: 8 Mbit/s
  • 30. 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
  • 31. Client/Server- e.g. a file server Clients Other computers on network Thin client – no processing Server Controls the network Hard disk holding shared files Organization of Resources
  • 32. 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  File Server System  Server does authentication and transmits file to client  Client does own processing  Benefits  Reduces volume of data traffic  Allows faster response for each client  Nodes can be less expensive computers Organization of Resources
  • 33. Peer-to-Peer Technology  All computers have equal status  Share data and devices as needed  Disadvantage – slow transmission Hybrid- Contains elements of various organizations to optimize transmission speed and organizational needs
  • 34. Protocol  Set of rules governing the exchange of data  Assists with coordination of communications  Was message received properly?  TCP/IP- Internet standard  Transmission Control Protocol / Internet Protocol  All computers in world speak same language
  • 36. Ethernet  Dominant protocol  Bus or star topology  Uses 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
  • 37. Ring topology- Token Ring  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
  • 38. Application of the network  File Transfer Software  Download- Receive a file from another computer  Upload- Send a file to another computer  Terminal Emulation Software  PC imitates a terminal for communication to mainframe  Micro-to-mainframe link
  • 39. Office Automation Communication Applications  E-mail  Facsimile (Fax)  Groupware  Teleconferencing  Video conferencing  ATM  Electronic fund transfers  Telecommuting  Online services  The Internet  Electronic data interchange (EDI)
  • 41. 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
  • 42. Contents  Data Communications  Network  Data Transmission  Communications Media  Network Topology  Local Area Network  Wide Area Network  Organization of Resources  Protocol  Software  Communication Applications

Editor's Notes

  1. ISDN- Integrated Services Digital Network Digital transmission Speeds of 128,000 bps Connect and talk at same time Need Adapter Upgraded phone service Initial costs high Ongoing monthly fees may be high Not available in all areas
  2. A hub is a simple device that sends all data to all devices connected to the hub. A hub provides no error checking, and no filtering, it simply forwards everything. Every device connected to a hub shares the same broadcast domain and so is in the same collision domain. Sometimes hubs are divided into passive and active. A passive hub does nothing except provide a path fo A bridge is used to connect two networks, and therefore has one port for each network. A bridge operates at the Data Link layer (layer 2) of the OSI model; therefore, it can read the MAC (Media Access Control) addresses in the data packets. A bridge has internal RAM. When a bridge first starts up, it behaves like a hub. But as the bridge receives packets from each network, it builds a table of the source MAC addresses on each segment.r the data. An active hub regenerates the signal before sending it along. The operation of the switch is almost identical to that of a bridge. The MAC address table of a switch is built by inspecting the source MAC address of frames. Forwarding decisions are made using the destination address of frames. When the switch receives a frame, it looks at the destination MAC address and then forwards it out only the port associated with that MAC address. Like a bridge, a switch will always forward all broadcast and frames with unknown destinations to every port, with the exception of the port on which the transmission originated. Routers Forward packets based on information at layer 3 and above Establish network address translation (NAT) boundaries Terminate virtual circuits (VPNs) Encrypt and decrypt traffic Implement complex filters (stateful inspection, routing policy, etc.) Support modular physical interfaces of several types Switches Forward packets (frames, if you prefer) primarily at layer 2 Aggregate many connections into a few higher-bandwidth links Provide a much higher-throughput backplane Include mostly fixed copper or fiber Ethernet interfaces
  3. Before the digital T-1 system, carrier wave systems such as 12-channel carrier systems worked by frequency division multiplexing; each call was an analog signal.