The document discusses computer networks and data communications. It describes how networks allow computers to be connected over long distances to share resources and process data in a distributed manner. The key components of a network include sending and receiving devices connected by a communications link. Different types of networks exist depending on the distance between nodes, from local area networks (LANs) to wide area networks (WANs). The document outlines various methods for data transmission, network topologies, protocols, and applications of computer networking.

1. Networking- Computer Connections
Chapter 7

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

26. Bridged Network Ring

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

35. Protocol …

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)

40. !@#$%^&*

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