1. Computers Are Your Future
© 2005 Prentice-Hall, Inc.

2. Computers Are Your Future
Chapter 6
Networks: Communicating and
Sharing Resources
© 2005 Prentice-Hall, Inc

3. What You Will Learn About
Basic networking concepts
The three major types of physical media
Bandwidth
How modems transform digital computer signals into analog signals
Circuit switching and packet switching networks
© 2005 Prentice-Hall, Inc

4. What You Will Learn About
The importance of protocols in a computer network
The advantages of a network
Peer-to-peer and client/server LANs
The most widely used LAN protocol
Ways that businesses use WANs
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5. Network Fundamentals
A computer network consists of two or more computers linked together to exchange data and share resources.
Communications is the process of sending and receiving messages.
Communications channels are the paths through which messages are passed.
Communications devices transform electronic signals.
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6. Physical Infrastructure
Physical infrastructure refers to cables, modems, switches, and routers.
Twisted-pair – Two insulated wires twisted around each other; the same type of wire as that used for telephones
Types of twisted-pair technologies:
Leased line (T1)
Integrated Services Digital Network (ISDN)
Digital Subscriber Line (DSL)
Coaxial cable – Consists of an insulated center wire surrounded by a layer of braided wire; the same type of wire as that used for cable TV
Fiber-optic cable – Type of fiber glass cable that transmits data in the form of light impulses; can carry more data for longer distances than other wire
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7. Bandwidth
Bandwidth is the amount of data that can be transmitted through a communications channel.
Digital bandwidth is measured in bits per second (bps), kilobits per second (Kbps), megabits per second (Mbps), or gigabits per second (Gbps).
Low bandwidth is 56 Kbps and high bandwidth is 622 Mbps.
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8. Modems: From Digital to Analog and Back
Modulation
Analog
Digital
Demodulation
Digital
Analog
Modems are devices that transform signals when sending and receiving transmissions.
Modulation – Transforming digital signals to analog
Demodulation – Transforming analog signals to digital
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9. Modems: From Digital to Analog and Back
Internal Modem
External Modem
Two types of modems:
Internal modems – Fit into a computer’s expansion slot
External modems – Connect to a port outside the system box
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10. Asynchronous and Synchronous Communications
Asynchronous communication is a method of networking in which bits of data are sent and received one bit at a time; each byte contains a start and stop bit.
Synchronous communication requires a synchronization signal that identifies units of data.
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11. Modulation Protocols
Modulation protocols are communications standards that modems conform to.
Data transfer rate is the rate at which two modems can exchange data. It is measured in bits per second (bps).
A modulation protocol called V.90 enables modems to transfer data at 56 Kbps.
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12. Cable Modems
Cable modems enable computers to access the Internet by way of a cable TV connection.
Data is transferred through a coaxial cable.
Bandwidths range from 500 Kbps to 1 Mbps.
Bandwidth is divided among the number of subscribers using it.
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13. Switching and Routing Techniques
Packet switching
Outgoing messages are divided into fixed-size data units called packets.
Packets are numbered and addressed to the receiving computer.
Routers examine the packets and send them to their destination.
Circuit switching
Networks create an end-to-end circuit between the sending and receiving computers.
Electronic switches establish and maintain the connection.
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14. Advantages and Disadvantages of Circuit and Packet Switching
Circuit switching
Voice and real-time transmission
No delivery delays
Costly
A direct electrical connection between the computers is required
Packet switching
Efficient, less expensive, and reliable
Will function if part of the network is down
Delays in receiving packets
Not ideal for real-time voice communication
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15. Protocols
Protocols are fixed, formalized standards that specify how computers can communicate over a network.
Protocol suite – The total package of protocols that specify how a network functions
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16. Network Layers
user
physical media
receiving
sending
protocol
layer
stack
Network architecture is the overall design of a network.
The network design is divided into layers, each of which has a function separate from that of the other layers.
Protocol stack – The vertical (top to bottom) arrangement of the layers; each layer is governed by its own set of protocols
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17. Advantages of Networking
Shared applications
Users share software
File server enables all users to work with the same application program
Building information resources
Users create common pools of data that can be accessed by employees
Reduced hardware costs
Users share equipment
Connected people
People can work together without being at the same location
Groupware enables sharing of schedules and communications
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18. Types of Computer Networks
Local Area Network (LAN)
Links computers within a building or group of buildings
Uses direct cables, radio, or infrared signals
Wide Area Network (WAN)
Links computers separated by a few miles or thousands of miles
Uses long-distance transmission media
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19. Local Area Networks (LANs)
Network access is controlled by a network administrator.
Users can access software, data, and peripherals.
LANs require special hardware and software.
Computers connected to a LAN are called workstations or nodes.
Types of LANs:
Peer-to-peer
Client-server
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20. LAN Hardware and Software
Networking Hardware
Network interface card (NIC) – Provides the connection between the computer and the network
Inserted into a computer’s expansion slot
Networking Software
Operating system that supports networking (Unix, Linux, Windows, Mac OS)
Additional system software
NIC
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21. Peer-to-Peer Networks
All computers on the network are treated as equal.
There are no file servers.
Users decide which files and peripherals to share.
Peer-to peer is not suited for networks with many computers.
Peer-to-peer is easy to set up. Example: home networks
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22. Client-Server Networks
Typical corporate networks are client-server.
Client-server requires various topologies or physical layouts.
The network requires file servers, networked computers (clients), and a network operating system (NOS).
Clients send requests to servers for programs and data, and to access peripherals.
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23. LAN Topologies The physical layout of a LAN is called its topology.
Topologies resolve the problem of contention, which occurs when multiple users try to access the LAN at the same time.
Collisions or corrupt data occur when different computers use the network at the same time.
Ring topology
Bus topology
Star topology
All workstations are attached in a circular arrangement
A special unit of data called a token travels around the ring
Workstations can only transmit data when they possess a token
Called a daisy chain
Every workstation is connected to a single cable
Resolves collisions through contention management
Difficult to add workstations
Contains a hub or central wiring concentrator
Easy to add workstations
Resolves collisions through contention management
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24. Wide Area Networks (WANs)
WANs are similar to long-distance telephone systems.
They have a local access number called a point of presence (POP).
They contain long-distance trunk lines called backbones.
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25. Transaction Acquisition
WAN Applications
LAN-to-LAN
WANs are used to connect LANs at two or more geographic locations.
Companies use WANs to connect their branches to one network system.
Transaction Acquisition
Information about transactions is instantly relayed to the corporate headquarters.
Point-of-sale (POS) terminals relay transactions to central computers through WANs.
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26. Backbones
Backbones, high-capacity transmission lines, are regional, continental, or transcontinental.
Internet backbones can carry 2.5 gigabits of data per second.
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27. WAN Protocols
X.25 is the oldest packet switching protocol. It is used by automated teller machines and credit card authorization devices.
New protocols designed for digital lines and faster data transfer rates are:
Switched Multimegabit Data Service (SMDS)
Asynchronous Transfer Mode (ATM)
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28. Public Data Network (PDN)
PDN is a for-profit data communications network.
Fees are paid on a per-byte-transferred basis.
They offer good security and network availability.
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29. Virtual Private Network (VPN)
A virtual private network consists of lines that are leased to a single company.
The network is not open to the public.
It is the most secure type of WAN.
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30. Chapter 6 Summary
Computer networks link two or more computers to exchange data and share resources.
Two types of computer networks:
Local area network (LAN)
Wide area network (WAN)
Computer networks:
Reduce hardware costs
Enable users to share applications
Provide a means to pool an organization’s data
Foster teamwork
Computer networks require physical media such as telephone wire, coaxial cable, or fiber-optic cable to connect the computers.
© 2005 Prentice-Hall, Inc

31. Chapter 6 Summary continued
Modems transform analog and digital signals.
Network protocols enable the network to function smoothly.
Data is sent through the network by switching and routing techniques.
LAN topologies include:
Bus topology
Star topology
Ring topology
Wide area networks are used to link computers throughout the world.
© 2005 Prentice-Hall, Inc