1. Chapter 5
LANs

2. Chapter Contents Section A: Network Building Blocks
Section B: Wired Networks
Section C: Wireless Networks
Section D: Using LANs
Section E: Security Through Encryption
Chapter 5: LANs and WLANs

3. Network Building Blocks
Network Classifications
LAN Standards
Network Devices
Clients, Servers, and Peers
Physical Topology
Network Links
Communications Protocols
Chapter 5: LANs and WLANs

4. Network Classifications
Personal Area Network (PAN) – interconnection of personal digital devices
Neighborhood Area Network (NAN) – connectivity spread over several buildings
Local Area Network (LAN) – usually connects computers in a single building
Metropolitan Area Network (MAN) – public high-speed network with range of about 50 miles
Wide Area Network (WAN) – consists of several smaller networks
Chapter 5: LANs and WLANs

5. LAN Standards
LAN technologies are standardized by the Institute of Electrical and Electronics Engineers (IEEE) Project 802 – Local Network Standards
IEEE specifies the standards for Ethernet wired local area networks
How devices physically signal each other, how devices “share the wire in the wall”, etc.
Ethernet is the de facto standard for wired LAN in use today
Chapter 5: LANs and WLANs

6. Network Devices
Each connection point on a network is referred to as a node
To connect to a LAN, a computer requires network circuitry, sometimes referred to as a network interface card (NIC)
adapter
A networked peripheral, or network-enabled peripheral, is any device that contains network circuitry to directly connect to a network
printers, scanners, copiers
A network device, or network appliance, is any electronic device that broadcasts/re-broadcasts network data, boosts signals, or routes data to its destination
routers, switches, modems, gateways, hubs, repeaters
What is a server?
Networked peripherals – printers, scanners, copiers, etc. …. Q: what is a server? Networked peripheral or network device
Network devices – routers, switches, modems, gateways, hubs, repeaters etc.
Chapter 5: LANs and WLANs

7. Network Devices
Figure 5-3
Chapter 5: LANs and WLANs

8. Clients, Servers, and Peers
Network devices can function as clients or as servers
Application server
File server
Print server
Networks that include one or more servers can operate in client/server mode
Peer to Peer(without server)
Figure 5-4 and 5-5
Chapter 5: LANs and WLANs

9. Physical Topology
The arrangement of devices in a network is referred to as its physical topology
Star: central connection point
Ring: attached to 2 neighbors
Bus: common, shared backbone
Mesh: multiple interconnections
Tree: stars on a bus
What are the advantage of each
Topology?
Figure 5-6
Chapter 5: LANs and WLANs

10. Can various network be interconnected?
Same networks can be connected by a device called repeater
Two similar networks can be connected by a device called a bridge (or switch)
Gateway is a generic term for any device or software code used to join two networks
Router(to connect your home LAN to the Internet)
Chapter 5: LANs and WLANs

11. Network Links Communication Media
Guided(Wired)
Unguided(Wireless)
A communications channel, or link, is a physical path or frequency for signal transmissions
Bandwidth is the transmission capacity of a communications channel (usually expressed in bits/sec, bps)
Broadband
Narrowband
Figure 5-7
Chapter 5: LANs and WLANs

12. Communications Protocols
Rules (Standards) for efficiently and effectively transmitting data from one network node to another. They define how to:
Divide messages into packets
Affix addresses (of the nodes) to packets
Initiate transmission (arbitrate access)
Regulate flow of data
Check for transmission errors
Acknowledge receipt of transmitted data (in some protocols)
arbitrate 
英[ˈɑ:bɪˌtreɪt] 
美[ˈɑrbɪˌtret] 
过去式：arbitrated 过去分词：arbitrated 现在分词：arbitrating
基本释义 同反义词 相关资料
vt. & vi. 1.仲裁, 公断
affix 
英[ˈæfɪks] 
美[ˈæfɪks] 
基本释义 相关资料
vt. 1.粘贴 2.附加；加(附言)，附上(签名等)，(尤指在末尾)添上 3.盖(印章)；(在邮票上)盖(邮戳) 4.加以，把…加在(某人)头上，把(责备、罪责、嘲笑等)加诸
n. 1.附加物，添加物，添加剂 2.附件，附录 3.<语法>词缀
及物动词 vt.
1.粘贴 affix a label to a bottle
在瓶子上贴一张标签
He affixed the sign to the wall.
他将标记贴到墙上。
2.附加；加(附言)，附上(签名等)，(尤指在末尾)添上 She affixes her real name to her writings.
她的著作都署上真名。
He affixed his signature to the document.
他在那份文件上签了名。
3.盖(印章)；(在邮票上)盖(邮戳) affix a seal
打上图章
Chapter 5: LANs and WLANs

13. Packet
When you send a file ,you might suppose that it is transmitted as an entire unit to its destination?
File is actually choppd up into small pieces
A packet 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(payload)
payload 
英[ˈpeiˌləud] 
美[ˈpeˌlod] 
基本释义
n. 1.有效载荷 2.（车辆等的）装载货物，装载量 3.（炸弹、导弹的）爆炸力，炸药量 4.（航天器、卫星的）装备
名词 n.
1.有效载荷
Chapter 5: LANs and WLANs

14. Ethernet Frame Structure
IEEE Ethernet frame
Type
64 – 1518 bytes in length
Preamble: 8 bytes
7 bytes with pattern , followed by one byte with pattern (frame delimiter)
used to synchronize receiver, sender clock rates
Addresses: 6 bytes, frame is received by all adapters on a LAN and dropped if address does not match
Type (Length): 2 bytes, length of data segment (min. 46 bytes)
CRC (Cyclic Redundancy Check): 4 bytes, created by sender, checked by receiver, if error detected, the frame is simply dropped
Chapter 5: LANs and WLANs

15. Why not just send an entire file?
Circuit-switching technology vs.
Packet switching technology
The Internet
Voice over IP (VoIP)
Advantages of one vs. the other?
Figure 5-11
Chapter 5: LANs and WLANs

16. Communications Protocols
Every packet that travels over a packet-switched network includes the address of its destination device
Most physical devices have more than one address
A MAC address is a unique number assigned to a network interface card when it is manufactured
An IP address is a series of numbers used to identify a network device in an internet
IP addresses can be assigned by registration, or obtained dynamically through DHCP
Chapter 5: LANs and WLANs

17. QuickCheck page 207/255
Chapter 5: LANs and WLANs

18. Wired Networks Wired Network Basics HomePNA and Powerline Networks
Ethernet
Ethernet Equipment
Ethernet Setup
Chapter 5: LANs and WLANs

19. Wired Network Basics
A wired network uses cables to connect network devices
Wired networks are fast, secure, and simple to configure and well-proven
Devices tethered to cables have limited mobility
Figure 5-12
tether 
英[ˈteðə] 
美[ˈtɛðɚ] 
过去式：tethered 过去分词：tethered 现在分词：tethering复数：tethers
基本释义 词组习语 同反义词 相关资料
n. 1.(拴牲畜用的)系绳;系链 2.(能力等的)限度,范围
Chapter 5: LANs and WLANs

20. HomePNA and Powerline Networks
HomePNA (HPNA) networks utilize existing telephone wiring to connect network devices
Special NICs and cables are required
Powerline networks transmit data over power lines as low-frequency radio waves
Figures 5-13 and 5-14
Chapter 5: LANs and WLANs

21. Ethernet
Simultaneously broadcasts data packets to all network devices (a star topology)
IEEE defines the Ethernet protocol
CSMA/CD protocol used to share the channel
Vary in speed from 10Mbps to 10Gbps
Figure 5-15
Chapter 5: LANs and WLANs

22. Ethernet-
On an Ethernet, data travels on a first come, first served basis. If two workstations attempt to send data at the same time, a collision occurs.
That data must be resent.
Figure 5-16
CSMA-Carrier Sense Multiple Access with Collision Detection
Chapter 5: LANs and WLANs

23. Ethernet Equipment Checking a workstation for an Ethernet port
Figure 5-18
Chapter 5: LANs and WLANs

24. Ethernet Equipment
Ethernet adapter - NIC (designed to support the Ethernet protocols)
Network hub
Network switch
Network router
RJ45 connector
Figures 5-19 and 5-20 and 5-21
Chapter 5: LANs and WLANs

25. Typical Ethernet Setup
Technically, this device functions as an Ethernet switch, as well as an IP router.
Chapter 5: LANs and WLANs

26. Quickcheck 216/264
Chapter 5: LANs and WLANs

27. Wireless Networks Wireless Basics Bluetooth Wi-Fi Wi-Fi Equipment
Wi-Fi Setup
Chapter 5: LANs and WLANs

28. Wireless Basics Advantage
A wireless network transports data from one device to another without cables or wires
RF signals(Radio wave)
Transceiver
A combination of a transmitter
And a receiver
Microwaves
Infrared light
Advantage
Disadvantage
Speed,range,licensing,Security concerns
Slower than wired networks
Figure 5-25
Radio frequency signal
antenna [æn'tɛnə] 
[词典释义] n. 1. 【动】触角,触须 2. 【无】【美】天线
[网络释义] antenna 1.天线;触角 2.标志杆 3.大触角 ANTENNA 1.天线 2.大线 Antenna 1.天
Chapter 5: LANs and WLANs

29. Most popular technologies
Wi-Fi
Bluetooth
WiMAX
Fixed internet access
Zigbee
Internet of things
Chapter 5: LANs and WLANs

30. Bluetooth
Bluetooth is a short-range, wireless network technology designed to make its own connections between electronic devices, without wires, cables or any direct action from a user
a piconet
Peak transmission rates of only 1Mbps(version1.2) or 3Mbps(Version 2.0+EDR) over a range of 3-300feet
“Bluetooth” - from 10th century Danish King, Harald Bluetooth
Chapter 5: LANs and WLANs

31. Wi-Fi
Wireless networking technologies that are compatible with Ethernet (per IEEE )
MIMO technology uses two or more antennae to send multiple sets of signals
Figure 5-29
antennae
[æn'teni:]
添加生词
改进词条
an·ten·nae
n. 天线, [动]触须, 触角, 直觉 名词antenna的复数形式
Chapter 5: LANs and WLANs

32. Wi-Fi Equipment
Figure 5-31
Chapter 5: LANs and WLANs

33. Wi-Fi Equipment
If your computer is not pre-equipped with wireless circuitry, you can purchase and install a Wi-Fi card
Figure 5-33
Chapter 5: LANs and WLANs

34. Wi-Fi Equipment Wireless network setups Wireless ad-hoc network
Wireless infrastructure network
Wireless access point
Wireless router
Figure 5-34
Chapter 5: LANs and WLANs

35. Wi-Fi Setup(9-steps) Set up the router
Connect to the router with a computer
Configure the router
Access the router setup utility
Create a new router password
Chapter 5: LANs and WLANs

36. Wi-Fi Setup Enter an SSID for the network
Activate WEP, WPA, or WPA2 and create an encryption key(!!)
Set up the wireless workstations
Connect an Internet access device
Generally a modem that will connect to the service available in your area (cable, DSL, etc.) from your service provider (ISP)
Chapter 5: LANs and WLANs

37. Typical Wi-Fi Setup
Figure 5-35
Chapter 5: LANs and WLANs

38. Quick 225/273
Chapter 5: LANs and WLANs

39. Using LANs LAN Advantages and Challenges Sharing Files
Sharing Printers
LAN Parties
Troubleshooting
Chapter 5: LANs and WLANs

40. LAN Advantages 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 (read “expensive”)
Chapter 5: LANs and WLANs

41. Chapter 5: LANs and WLANs

42. LAN Challenges Resources become unavailable when network malfunctions
Networks may be vulnerable to unauthorized access
More vulnerable than standalone computers
Wireless networks can be tapped from a “snooping” computer
Networked computers are susceptible to an increasing number of worms, Trojan horses, and blended threats
Chapter 5: LANs and WLANs

43. Sharing Files
If you use Windows, it automatically detects available LANs any time you turn on a workstation
To connect to a shared resource, you might be asked for a user ID and password
Figure 5-41
Chapter 5: LANs and WLANs

44. Sharing Files In this drive mapping example, a server’s drive
C is mapped as drive F
by a workstation. After the mapping is complete, the server’s hard disk appears in the workstation’s directory as drive F and can be used just as though it were a drive connected directly to the workstation.
Figure 5-42
Chapter 5: LANs and WLANs

45. Sharing Files
To allow other network users to access files or folders on your Windows computer, you have to designate them as shared (commonly, via Windows Explorer)
Figure 5-43
Chapter 5: LANs and WLANs

46. File Server
a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files (such as documents, sound files, photographs, movies, images, databases, etc.) that can be accessed by the workstations that are attached to the computer network.
The term server highlights the role of the machine in the client–server scheme, where the clients are the workstations using the storage.
A file server is usually not performing any calculations, and does not run any programs on behalf of the clients.
It is designed primarily to enable the rapid storage and retrieval of data where the heavy computation is provided by the workstations.
File servers are commonly found in schools and offices and rarely seen in local internet service providers using LAN to connect their client computers.
Chapter 5: LANs and WLANs

47. Sharing Printers Three setups allow for printer sharing:
Set up printer sharing using a workstation printer
Set up printer sharing using a print server
Install printer with built-in networking
Figure 5-45
Chapter 5: LANs and WLANs

48. Sharing Printers
In Windows, use the Printers and Faxes dialog box to allow other users to share the printer attached to your workstation
Figure 5-46
Chapter 5: LANs and WLANs

49. P233/281
Chapter 5: LANs and WLANs

50. Security Through Encryption
Wi-Fi Security
Encryption
Chapter 5: LANs and WLANs

51. Wi-Fi Security
Wireless networks are much more susceptible to unauthorized access and use by casual users than wired networks
LAN jacking, or war(wireless access revolution) driving, is the practice of intercepting wireless signals by cruising through an area
NetStumber
Figure 5-50
Chapter 5: LANs and WLANs

52. Wi-Fi Security
Wireless encryption scrambles data transmitted between wireless devices and then unscrambles the data only on devices that have a valid encryption key
WEP (Wired Equivalent Privacy)
WPA (Wi-Fi Protected Access)
WPA2
Activate encryption by using a wireless network key
Chapter 5: LANs and WLANs

53. Encryption
Encryption transforms a message so that its contents are hidden (encrypted) from unauthorized readers
Plaintext has not yet been encrypted
An encrypted message is referred to as ciphertext
Decryption is the opposite of encryption
Cryptographic algorithm
Cryptographic key
Chapter 5: LANs and WLANs

54. Encryption Weak vs. strong encryption
AES (Advanced Encryption Standard)
Encryption methods can be broken by the use of expensive, specialized, code-breaking computers
Brute-force method
Chapter 5: LANs and WLANs

55. Encryption
Public key encryption (PKE) eliminates key-distribution problem, by using one key to encrypt a message and another key to decrypt the message
Figure 5-55
Chapter 5: LANs and WLANs

56. The Idea of Public Key Cryptography
Put (lock, locking key) in the public domain, i.e., in a post office.
Anyone who wants to send me a letter confidentially can do the following:
Buy a strong box
Use my lock with the locking key to lock the letter inside.
Send me the locked box.
Locking key
Unlocking key

57. Encryption with a Public Key System
(k , k ) is the key pair
of Alice
Bob e d
Alice
file
file
encryted
file m m
E (m)
Alice’s
public
Key k k
Alice’s
Private
Key k e e d

58. Digital Signature with a public key system
Bob
(k , k ) is Bob’s
key pair
Alice e d m m
m||D (f(m)) k d f
D (f(m))
f(m)
f(m) k d

59. Key Exchange with a Public Key System
(k , k ) is the key pair
of Alice
Bob e
Alice d
session
key
encryted
sess. key
session
key k k
E (k)
Alice’s
public
Key k k
Alice’s
Private
Key k e e d
Bob generates the session key k, sends Alice the encrypted session key.

60. Chapter 5 Complete
LANs and WLANs