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Transcript of Computers Are Your Future Chapter 8 Computers Are Your Future © 2008 Prentice-Hall, Inc.
Computers Are Your Future Chapter 8
© 2008 Prentice-Hall, Inc. Slide 2
Computers Are Your Future
Chapter 8
Networks: Communicating and Sharing Resources
Computers Are Your Future Chapter 8
© 2008 Prentice-Hall, Inc. Slide 3
Network Fundamentals
A computer network consists of two or more computers linked together to exchange data and share resources.
•LAN – local area network (small geographic area)
•WAN – wide area network (large geographic area)
Computers Are Your Future Chapter 8
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Communication Devices
Convert data into signals. Transform data from
analog into digital signals and back.
Computers, modems, routers, switches, wireless access points, and network interface cards are all communication devices.
modems
routers
switches
Network Interface Cards
computers
Computers Are Your Future Chapter 8
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Communication Devices
Workstations – computer connected to a networkCalled clientsContains a network interface card (NIC)
Computers Are Your Future Chapter 8
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Communication Devices
Routers – connect two or more LANs or WANsCan determine the best path to route data.LANs often use switches which are similar to routers.
Computers Are Your Future Chapter 8
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Communication Devices
File serverHigh capacity, high speed computerLarge hard driveContains a network operating system (NOS)
Computers Are Your Future Chapter 8
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Network Fundamentals
Network administrators InstallMaintainSupport Interact with usersTroubleshoot problems
Computers Are Your Future Chapter 8
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Advantages of Networks
Reduced hardware costs Application sharing Sharing information
resources Centralized data
management Connecting people
Computers Are Your Future Chapter 8
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Disadvantages of Networks
Loss of autonomy Lack of privacy Security threats Loss of productivity
Computers Are Your Future Chapter 8
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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
Computers Are Your Future Chapter 8
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LAN Hardware and Software
Networking HardwareNetwork interface card
(NIC) – Provides the connection between the computer and the network
Inserted into a computer’s expansion slot
Networking SoftwareOperating system that
supports networking (Unix, Linux, Windows, Mac OS)
Additional system software
NIC
Computers Are Your Future Chapter 8
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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.
Computers Are Your Future Chapter 8
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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.
Computers Are Your Future Chapter 8
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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. Click to see examples.
Bus topology• Called a daisy chain• Every workstation is connected to
a single cable• Resolves collisions through
contention management• Difficult to add workstations
Star topology• Contains a hub or central wiring
concentrator• Easy to add workstations• Resolves collisions through
contention management
Ring 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
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Protocols
Protocols are fixed, formalized standards that specify how computers can communicate over a network.
A protocol suite is the total package of protocols that specify how a network functions.
Computers Are Your Future Chapter 8
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Network Layers
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. The protocol stack is the vertical (top to bottom)
arrangement of the layers; each layer is governed by its own set of protocols.
user
physical media
user
physical media
receiving
sending
protocol
layerstack
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Ethernet Protocol Ethernet uses a protocol called Carrier Sense Multiple Access/
Collision Detection (CSMA/CD) CSMA/CD works as follow:
1. Sender senses the media for a fixed time2. Sender computer place a data unit with fixed size (packet), the
packet contains the address of the receiver plus the data, now two possibilities
3. If no other computer were sending at the same time, The packet will reach the destination, the distention will confirm by sending an acknowledgement back to the sender. If another computer was sending at the same time, collision will occur and both packets will not reach their destinations.
4. As a result of collision, no acknowledgement is sent to the sender . The sender in this case will assume the packet has not reached the distention and resend it again after waiting for some random time interval.
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No collision
Ethernet Protocol
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A and C transmit at the same time => collisionA and C will re-transmit after a random time => Collision avoidance
Ethernet Protocol
A B
C
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Wi-Fi
Wireless-fidelityWireless LANUses a central access pointAdvantages
• Fast (11 Mbps)• Reliable• Long range• Integrates with existing networks
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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.
Computers Are Your Future Chapter 8
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Backbones
Backbones, high-capacity transmission lines, can be regional, continental, or transcontinental.
Internet backbones can carry 2.5 gigabits of data per second.
Computers Are Your Future Chapter 8
The internet protocol
The internet protocols collectively called Transmission Control Protocol/Internet Protocol TCP/IP
IP enables direct and immediate contact between one computer another. A computer can contact another by dialing the other computer’s IP address.
TCP defines how the connection is established between 2 computers
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Computers Are Your Future Chapter 8
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Circuit switchingNetworks create an end-
to-end circuit between the sending and receiving computers.
Electronic switches establish and maintain the connection.
Switching and Routing Techniques
Packet switchingOutgoing 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.
Computers Are Your Future Chapter 8
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Advantages Disadvantages
Circuit switchingVoice 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
Advantages and Disadvantages of Circuit and Packet Switching
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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)
Computers Are Your Future Chapter 8
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WAN Applications
LAN-to-LANWANs are used to connect
LANs at two or more geographic locations.
Companies use WANs to connect their branches to one network system.
Transaction AcquisitionInformation 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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Chapter 8 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
Peer-to-peer uses no file server.
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Chapter 8 Summary continued
Network topologies are the physical layout of a LAN. LAN topologies include:
• Bus topology
• Star topology
• Ring topology Protocols define how devices communicate with each
other. Ethernet is the most widely used LAN protocol.
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Chapter 8 Summary (continued)
Point of presence (POP) is a WAN connection point.
Circuit switching creates permanent end-to-end circuit that is optimal for voice and real-time data.
Packet switching does not require a permanent switched circuit.