Download Wireless Networks

Chapter 5
LANs And WLANS
(了 解)
Contents
Network Building Blocks (Section A)
Wired Networks (Section B)
Wireless Networks (Section C)
Using LANs (Section D)
Security Through Encryption (Section E)
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CHAPTER OBJECTIVES
Describe the characteristics of PANs(个人域网), NANs,
LANs, MANs(区域网), and WANs
Diagram the five most common network topologies(拓扑)
Diagram Shannon's model of a communications network
List the types of cables and other links typically used for
data communications networks
Make a list of network devices and explain the role of
each one
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CHAPTER OBJECTIVES
Describe the role of communications protocols
Explain the difference between packet switching and
circuit switching technology
Describe how to set up wired and wireless networks
List various ways to share files over a LAN
List security measures for wired and wireless networks
List and define types of encryption(加密) that help
secure computer networks and data
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Section A Network Building Blocks
Network Classifications
P198-199
How are computer networks classified?
Networks can be classified according to their size and geographic scope.
A PAN.---- (personal area network) refers to the interconnection of personal
digital devices within a range of about 30 feel and without the use of wires or
cables.
 A NAN (neighborhood area network) provides connectivity within a limited
geographical area, usually spread over several buildings.
 A LAN ---(local area network) connects personal computers within a very
limited geographical area-usually a single building.
A MAN ----(metropolitan area network) is a public high-speed network capable
of voice and data transmission within a range of about 50 miles (80 km).
A WAN -----(wide area network) covers a large geographical area and usually
consists of several smaller networks.
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LANs Standards
P199
What are LAN standards ?
LAN technologies are standardized by the Institute of
Electrical and Electronics Engineers (IEEE) Project 802Local Network Standards.
 What are the most popular LAN standards?
Several LAN standards including ARCnet, Token Ring,
and FDDI(光纤分布数据接口), were popular in the past.
Today, most LANs are configured with Ethernet
technology and use compatible Wi-Fi standards in
applications that require wireless access.
More specifics about these in sections B and C.
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Network device
such as Router ,
hub , switch,
repeater.
Network
Peripheral
Such as
printer,
scanner
Storage
device
Computer
Network Devices
P200
Network
interface card
(NIC)
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Client, Servers ,And Peers
P201
 What is the difference between a network client
and a server?
A server is a computer that provides services to other
computers called clients.
Application Server
File Server
Print Server
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Client, Servers ,And Peers
P201
Can a network function without a server?
Files and applications can he shared among workstations
operating in peer-to-peer mode.
A network can function in client/server mode when necessary
and also exchange data in peer-to-peer fashion.
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参考：
http://docs.huihoo.com/p2p/1/index.html
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Physical Topology p202
How are the devices on a LAN physically arranged?
The arrangement of devices in a network is referred to as its
physical topology.
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Physical Topology p202
Can various networks he interconnected?
Yes.
Two similar networks can be connected by a device called a
bridge, which simply transfers data without regard to its format.
Networks that use different topologies and technologies can be
interconnected by using gateways(通道).
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Network Links p203
 What connects the nodes of a network ?
 Data in a network with wired links travels from one device to another over
cables
 Networks without wires transport data through the air
What's bandwidth ?
Bandwidth is the transmission capacity of a communications channel.
The bandwidth of a channel carrying digital data is usually measured in
bits per second (bps).
※ Broadband
※ Narrowband
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Communications Protocols
p204
 What is a protocol ?
A protocol is a set of rules for interacting(相互作用) and negotiating(处
理).
A communications protocol refers to a set of rules for efficiently
transmitting data from one network node to another.
The best-known communications protocol is probably TCP/IP.
 How does data over a network ?
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Communications Protocols
p205-207
Your file is chopped up(切开) into small pieces called packet to
transmit.
A packet(信息包) is a parcel of data that is sent across a computer
network. Each packet contains the address of its sender, the destination
address, a sequence number, and some data.
How are packets routed to their destinations?
Every packet that travels over a network includes the address of its
destination device.
Two commonly used addresses are
 MAC addresses :is a unique number assigned to a network interface
card when it is manufactured.
 IP addresses : is a series of numbers used to identify a network device.
such as 204.127.129.1
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Section B Wired Networks
Wired Networks Basics
p208-209
What is a wired network?
A wired network is one that uses cables to connect network
devices.
What are the advantages of wired networks?
Wired networks are fast, secure, and simple to configure.
What are the disadvantages of wired networks?
The cables that offer speed and security for a wired network
are also its main weakness.
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Wired Networks Basics p208-209
Today ,the most popular LAN technology is Ethernet.
Alternatives such as HomePNA and HomePlug technology
are available but much less frequently use.
有关HOMEPNA AND POWERLINE NETWORKS的相关知
识在P209-210，作为选学内容。
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Ethernet
p210-211
 How does Ethernet work?
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Ethernet
p211-216
 How fast is an Ethernet network(以太网 )?
What equipment do I need for an Ethernet network?
Two or more Ethernet-ready computers
An Ethernet router
Surge strip(防浪涌插座) or UPS
Cables for each computer
Internet access device, such as cable modem
or DSL modem and corresponding cables
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Ethernet Equipment
p212
HOW can I tell if a computer is Ethernet ready?
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Ethernet Setup
p214
What's the general procedure for setting up Ethernet?
Run Cables from the
router to each
workstation or server
Run a cable
between the router
and the device used
for your Internet
Connection
Configure each
workstation
Configure the router
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Section C Wireless networks
Wireless Networks Basic
P217
What Is a wireless network?
A wireless network transports data from one device to another
without the use of cables or wires. It transports data from radio
signals, microwaves, and infrared light.
How do radio signals transport data?
RF signals (radio frequency signals) are sent and received by a
transceiver (a combination of a transmitter and a receiver) that is
equipped with an antenna.
How do microwaves transport data?
Microwaves are electromagnetic signals. It can be aimed in a
single direction and have more carrying capacity than radio waves.
How do infrared(红外线) transport data?
Infrared can also carry data signals, but only for short distances
and with a clear line of sight.
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Wireless Networks Basic
P217-218
What are the advantages of wireless networks?
The main advantage of wireless networks is mobility.
What are the disadvantages of wireless networks?
The main disadvantages of wireless networks are speed, range,
licensing, and security.
Why is wireless slower than wired?
Wireless signals are susceptible(敏感的) to interference(干扰) from
devices . When interference affects a wireless signal, data must de
retransmitted.
What limits the range of a wireless network?
It can be limited by the type of signal, the transmitter strength, and
the physical environment.
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Wireless Networks Basic
P217-218
Note:
To make wireless network data useless to intruders(入侵者). it
should be encrypted(编码).
To broadcast at most frequencies, a license is required.
What are the most popular technologies for wireless
networks?
By far the most popular wireless LAN technology is Wi-Fi. A second
wireless technology called Bluetooth is useful for some applications.
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Bluetooth
P219
What is Bluetooth?
Bluetooth is a short-range wireless network technology that's
designed to make its own connections between electronic devices,
without wires, cables or any direct action from a user.
Where is Bluetooth use ?
Anyone can set up a Bluetooth network. Bluetooth connectivity
replaces the short cables that would otherwise tether (拴系)a
mouse, keyboard, or printer to a computer.
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Wi-Fi
P220
 What is Wi-Fi ?
Wi-Fi refers to a set of wireless networking technologies defined by IEEE
802.11 standards that are compatible with Ethernet.
A Wi-Fi network transmits data as radio waves over 2.4 GHz or 5.8 GHz
frequencies.
 How do the speed and range of Wi-Fi compare to
other network technologies?
Wireless network speed and range, are often theoretical maximums.
Although Wi-Fi 802.11n is capable of 200 Mbps speeds, in actual
performance it is unlikely to match Fast Ethernet and is far slower than
Gigabit Ethernet.
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Wi-Fi Equipment
P221
What equipment is required for a Wi-Fi
network?
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Wi-Fi Setup
p222
What's the general procedure for setting up Wi-Fi
network?
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Section D Using LANs
LAN Advantages And Challenges
p226-227
Why are LANs advantageous?
 LANs
enable people to work together
Sharing networked software can reduce costs
Sharing data on a LAN can increase productivity
Sharing networked hardware can reduce costs
 Sharing networked hardware can provide access to a
wide range of services and specialized peripheral devices
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LAN Advantages And Challenges
p226-227
Do LANs have disadvantages?
when a network malfunctions(失灵), all the resources
you're accustomed to accessing are unavailable until
the network is repaired.
their vulnerability(弱点) to unauthorized access.
more vulnerable than standalone computers to
malicious(怀恶意的) code.
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Sharing Files
p228
How do I access network resource?
If you use Windows, it automatically
detects available LANs any time you
turn on a workstation.
You can access shared data on other
workstations in a variety of ways.
Such as
Windows Explorer
Driver mapping
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Sharing Files
p229
How do I specify which resources can be shared by
other workstations?
You can allow other network users to view and edit files in the
folders you've designated as shared, or you can limit access only
to viewing.
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Sharing Files
p230
What is file server?
A file server is a computer whose primary purpose is to
be a repository(仓库) for files that can be accessed by
network workstations.
Are file servers a good idea for home networks?
Whereas file servers are an essential component of most
business networks, in many home networks, files are
stored on workstations in shared folders rather than on a
file server.
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Sharing Printers
p230
How can I set up a printer for network access?
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Sharing Printers
p231
How does printer sharing work?
① Connect the printer to one of the workstations
② Enable printer sharing
③ turn on printer and workstation
Any workstation on the network can send print jobs to the printer.
How do I enable printer sharing?
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Sharing Printers
p231
How do I send a print job to a shared printer?
you have to make sure that the printer driver is installed on
your computer
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Troubleshooting
p232
What if my network stops working?
Cables
Signal strength
Interference
Network devices
Security
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Section E Security Through Encryption
Wi-Fi Security p234
What are the threats to my wireless network?
wireless networks are much more susceptible to unauthorized
access and use.
Evil twin
LAN jacking
War chalking
How can I secure my wireless network?
Wireless encryption(编密码) scrambles(加密) the data
transmitted between wireless devices and then unscrambles the
data only on devices that have a valid encryption key.
What are the types of wireless encryption?
WEP
WPA
http://myhard.yesky.com/net/441/2152441.shtml
http://www.rcdaily.com.cn/html/wuxian/20080220/71.html
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Encryption
p237
Exactly what is encryption？
Encryption transforms a message in such a way that its contents are
hidden from unauthorized readers.
How does encryption work?
 An original message---one that has not yet been encrypted-is referred
to as plaintext(明文).
 An encrypted message is referred to as ciphertext(暗文).
 The process of converting plaintext into ciphertext is called encryption.
 The reverse process converting ciphertext into plaintext is called
decryption.
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Encryption
p237
What's the difference between strong and weak
encryption?
weak encryption is easy to decrypt even without the algorithm and
key.
Strong encryption is loosely defined as "very difficult to break."
How long does it take to break strong encryption ?
Encryption methods can be broken by the use of expensive,
specialized, code-breaking computers.
A 32-bit key
(232) numbers
less than a day
A 40-bit key
(240) numbers
a week
128-bit encryption and 256-bit encryption are probably secure for
several years. Most encryption today uses a 128-bit key.
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THE
END