1. Telecommunications and Networks
Chapter 6
Telecommunications
and
Networks

2. Overview of Communication
Communications is the transmission of a signal by way of a medium from a sender to a receiver.

3. Telecommunications
Electronic transmission of signals for communications
Telephone
Radio
Television
Lessens barriers of time and distance

4. Telecommunications Data communications Telecommunications media
Specialized subset of telecommunications
Includes the electronic collection, processing, and distribution of data
Telecommunications media
Anything that carries an electronic signal and interfaces between a sending device and a receiving device

5. Elements of a Telecommunications System
[Figure 6.3]

6. Analog and Digital Signals
Continuous fluctuations over time between high and low voltage
Digital
A discrete voltage state

7. Analog and Digital Signals
Analog signal
Fig. 6.4
Digital signal

8. Analog Waves Frequency Amplitude
The number of times per second a continuous wave completes one cycle
Amplitude
The difference of the extremes from the midpoint in a cycle

9. Basic Modulation Techniques
Amplitude modulation (AM)
Converts digital data to analog signals using a single frequency carrier signal
High-amplitude wave denotes a binary 1
Low-amplitude wave denotes a binary 0

10. Basic Modulation Techniques
Frequency modulation (FM)
Uses a constant amplitude carrier signal and two frequencies to distinguish between 1 and 0
Phase modulation
Uses a phase shift at transition points in the carrier frequency to represent 1 or 0

11. Communications Speed Bits per second (bps) Bandwidth Broadband
Number of bits that can be transferred in one second
Bandwidth
Range of signal frequencies that can be sent over a medium at the same time
Broadband
Bandwidth of 256,000 to 1 million bps

12. Types of Communications Media
Twisted wire cable
Coaxial cable
Fiber-optic cable
Microwave transmission
Cellular transmission
Infrared transmission

13. Twisted Wire Cable A cable consisting of pairs of twisted wires
The twist helps the signal from “bleeding” into the next pair

14. Coaxial Cable
Inner conductor wire surrounded by insulation, called the dielectric
Dielectric is surrounded by a conductive shield, which is in turn covered by a layer of nonconductive insulation, called the jacket

15. Fiber-Optic Cable
Consists of many extremely thin strands of glass or plastic bound together in a sheathing
Transmits signals with light beams

16. Wireless Transmission
Microwave: Terrestrial
Microwave: Satellite
Cellular
PCS

17. Telecommunications Devices
Modems
Fax modems
Special-purpose modems
Multiplexers
Communications processors

18. How a Modem Works

19. Multiplexers
Allow several telecommunication signals to be transmitted over a single communications medium concurrently
Time division multiplexer (TDM)
Multiple incoming signals are sliced into small time intervals
Frequency division multiplexer(FDM)
Incoming signals are placed on different frequency ranges

20. Time Division and Frequency Division Multiplexers
[Figure 6.14]

21. Communications Processors
Called front-end processors because they are in front of and before the main system CPU
[Figure 6.15]
Main
system
Front-end
processor
Incoming and
outgoing jobs

22. Telecommunications Carriers and Services
Common carriers
Long-distance telephone companies
Value-added carriers
Companies that have developed private telecommunications systems and offer their services for a fee

23. Telecommunications Carriers and Services
Switched line
Standard telephone line that uses switching equipment to allow one transmission device to be connected to others
Dedicated line
Provides a constant connection between two points
Also called a leased line

24. Telecommunications Carriers and Services
Private branch exchange (PBX)
Manages both voice and data transfer within a building and to outside lines
Wide area telephone services (WATS)
A billing method for heavy users of voiceband media
Phone and dialing services
Additional services from the common carriers (i.e. ANI)

25. Telecommunications Carriers and Services
Integrated services digital network (ISDN)
Technology that uses existing common-carrier lines to simultaneously transmit voice, video, and image data in digital form
Digital subscriber line (DSL)
Businesses/homes that have a DSL over existing phone wires can use a special modem that transmits up to 768 Kbps

26. Telecommunications Act of 1996
Completely rewrites the 62-year-old Communications Act
Goal: To promote competition and eliminate monopolies for a wide range of communication services
May cause profound changes in U.S. communications that can lead to a complete renovation in the way information is delivered to consumers

27. Global Telecommunications
One of the largest and fastest growing sectors of the global economies
Criticality of implementing and managing global networks
Increase of international acquisitions and mergers
Need to compete on a global basis

28. Computer Network
Includes communications media, devices, and software needed to connect two or more computer systems and/or devices
Benefits of a Network
Can turn a company into an agile, powerful and creative organization, giving it long-term competitive advantage
Can be used to share hardware, programs, and databases across the organization

29. Basic Data Processing Strategies
Centralized processing
All processing occurs in a single location
Decentralized processing
Processing devices are placed at various remote locations
Distributed processing
Computers at remote locations are connected to each other via telecommunications devices

30. Network Concepts and Considerations
Network topology
Logical models that describe how networks are structured or configured
Star network
A network that has a central hub or computer system

31. Four Basic Types of Network Topology
[Figure 6.17]
(a) ring
(b) bus
(c) hierarchical
(d) star

32. Types of Networks Local area networks (LAN) Regional networks
Connect computer systems and devices within the same geographical area
Regional networks
Tie regional areas together via telecommunications systems

33. Types of Networks Wide area networks (WAN) Private WANs
Tie large geographic regions together using microwave and satellite transmission or telephone lines
Private WANs
Computer equipment owned by users and data communications equipment provided by a common carrier
Value-added networks (VAN)
Offer services in addition to those offered by a traditional network (e.g., CompuServe)
International networks
Link system together between countries

34. Terminal-to-Host
“Dumb”
terminal
Fig 6.20
Applications and databases reside on the same host computer
User interacts with the application using a “dumb” terminal

35. LANs and WANs [Figure 6.18] [Figure 6.19]
A Typical LAN in a BUS Topology A Wide Area Network

36. File Server
Fig 6.21
Applications and databases reside on the same host computer
File server transfers data and programs to PCs on the network, which do the processing

37. Client/Server
Fig 6.22
Applications and databases reside on specialized host computers
Servers do most or all of the processing and transmit the results to the client

38. The Client/Server Approach
Advantages
Cost potential
Improved performance
Increased security
Disadvantages
Increased cost potential
Loss of control
Complex multivendor environment

39. Functions of Communications Software
Error checking
Message formatting
Communications logs
Data security and privacy
Translation capabilities for networks

40. Communications Software
Network operating systems
Systems software that controls the computer systems and devices on a network and allows them to communicate with each other
Network management software
Software tools and utilities available for managing networks

41. Communications Protocols
Open systems interconnection (OSI)
A protocol (or standard) endorsed by the International Standards Committee
TCP/IP
Developed by the U.S. government to link its defense research agencies
SNA
IBM’s communications protocol
Ethernet
A popular protocol often used with local area networks
Other protocols

42. Bridges, Routers, and Gateways
Connects two or more networks
Router
Features more sophisticated addressing software than bridges
Gateway
Links LANs or networks that employ different higher-level protocols

43. Bridges, Routers, and Gateways
[Figure 6.24]

44. Coordinating Communications and Networks
Polling
A procedure in which the main computer checks each device one at a time to see if there are any messages waiting to be communicated to other network devices
Token passing
A technique in which an electronic “token” is passed from one device to another
Contention
A procedure in which a device checks to see if a message is currently being transmitted

45. Data Transfer Modes Packet switching Frame relay
Communications process that divides electronic messages into small segments (data packets)
Frame relay
Uses wideband communications media and high speed switching devices
Voice-over frame relay
Moves voice traffic onto frame relay to bypass the public telephone network

46. Data Transfer Modes Asynchronous transfer mode (ATM)
A high-speed network technology that provides transport for voice, video, text, and other multimedia data
Fiber distributed data interface (FDDI)
Designed specifically to serve the needs of high-performance, mission-critical LAN applications

47. Telecommunications Applications
Links between PCs and mainframes
Facilitates the upload or download of data
Voice storage and forwarding
Sometimes called voice mail
Allows users to leave, receive, and store verbal messages for and from people around the world

48. Telecommunications Applications
Electronic mail
Users connected to a network can send messages to others by computer
Electronic document distribution
Involves transporting documents over communications lines and networks

49. Telecommunications Applications
Electronic software distribution
Involves installing software on a file server for users to share by signing onto the network and downloading the software onto their computers over the network
Telecommuting
Working at home on a PC and communicating with the central office or other workers via networks

50. Telecommunications Applications
Teleconferencing
Allows groups to have conferences in one connected voice phone call
Videoconferencing
An extension of teleconferencing that combines voice, video, and audio transmission

51. Telecommunications Applications
Electronic data interchange (EDI)
Uses network systems and follows standards and procedures that allow output from one system to be processed directly as input to other systems, without human intervention
[Figure 6.27]

52. Telecommunications Applications
[Figure 6.28]
Public network services
Give PC users access to vast databases and other services, usually for an initial fee plus usage fees

53. Telecommunications Applications
Specialized information systems
Include legal, patent, and technical information
Regional information systems
Include local electronic bulletin boards and electronic mail facilities that offer information regarding local club, school, and government activities
Distance learning
Extends the classroom by using telecommunications

54. Network Design Considerations
Reliability
Security
Response time
Privacy issues
Vendor services and support
Company support

55. Communications Audits
Purpose: To make sure the communications system is operating as intended
Types of communications audits:
Walk-thorough
Software check
Network check
Policy and procedures
Program and database check