Telecommunications

1
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
• 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

• Analog
• 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
• 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)
• 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

22
TelecommunicationsCarriers 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 Actof 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 Typesof Network Topology
Figure 6.17
(a) ring
(b) bus
(d) star
(c) hierarchical
32
Types of Networks

• Local area networks (LAN)
• 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)
• 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
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
• IBMs communications protocol
• Ethernet
• A popular protocol often used with local area
  networks
• Other protocols

42
Bridges, Routers,and Gateways

• Bridge
• 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
• 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