Transcript Networks - NYU Computer Science

Computers Are
Your Future
© 2005 Prentice-Hall, Inc.
Computers Are Your Future Chapter 6
Computers Are Your Future
Chapter 6
Networks: Communicating and
Sharing Resources
© 2005 Prentice-Hall, Inc
Slide 2
Computers Are Your Future Chapter 6
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
Slide 3
Computers Are Your Future Chapter 6
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
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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.
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 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
© 2005 Prentice-Hall, Inc
Slide 6
Computers Are Your Future Chapter 6
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).
 For example, low bandwidth could be 56 Kbps and
high bandwidth could be 622 Mbps.
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
Modems: From Digital to Analog and Back
Modulation
Analog
Digital
Demodulation
Analog
Digital
 Modems are devices that transform signals when sending
and receiving transmissions.
 Modulation – Transforming digital signals to analog
 Demodulation – Transforming analog signals to digital
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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.
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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.
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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 well over 1
Mbps.
 Bandwidth is divided among the number of
subscribers using it.
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
Switching and Routing Techniques
Packet switching
Circuit switching
 Networks create an endto-end circuit between the
sending and receiving
computers.
 Electronic switches
establish and maintain the
connection.
© 2005 Prentice-Hall, Inc
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.
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Computers Are Your Future Chapter 6
Advantages and Disadvantages of Circuit and
Packet Switching
Advantages
Disadvantages
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
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
Protocols
 Protocols are
fixed, formalized standards that specify
how computers can communicate over a network.
suite – The total package of protocols that
specify how a network functions
 Protocol
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
Network Layers
user
layer
physical media
receiving
sending
protocol
user
stack
physical media
 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
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
Advantages of Networking
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
© 2005 Prentice-Hall, Inc
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
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Computers Are Your Future Chapter 6
Types of Computer Networks
Local Area Network (LAN)
 Links computers within a
building or group of
buildings
Wide Area Network (WAN)
 Links computers separated
by a few miles or thousands
of miles
 Uses direct cables, radio, or  Uses long-distance
infrared signals
© 2005 Prentice-Hall, Inc
transmission media
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Computers Are Your Future Chapter 6
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
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
LAN Hardware and Software
Networking Hardware
Networking Software
Network interface card
Operating system that
(NIC) – Provides the
connection between the
computer and the network
Inserted into a computer’s
expansion slot
supports networking
(Unix, Linux, Windows,
Mac OS)
Additional system
software
NIC
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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.
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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.
Bus
Ring
Startopology
topology
•
•
•
•
•
•
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© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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.
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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.
© 2005 Prentice-Hall, Inc
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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Computers Are Your Future Chapter 6
Backbones
 Backbones,
high-capacity transmission lines, are
regional, continental, or transcontinental.
 Internet backbones can carry 2.5 gigabits of data per
second.
© 2005 Prentice-Hall, Inc
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Computers Are Your Future Chapter 6
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
Slide 27
Computers Are Your Future Chapter 6
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
Slide 28