Transcript Chapter 5

Basic Computer Application
Chapter 5
LANs
5 Chapter Contents
Section A: Network Building Blocks
Section B: Wired Networks
Section C: Wireless Networks
Section D: Using LANs
Section E: Security Through Encryption
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5
SECTION
A
Network Building Blocks
Network Classifications
LAN Standards
Network Devices
Clients, Servers, and Peers
Physical Topology
Network Links
Communications Protocols
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5 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 highspeed network with range of about 50 miles
Wide Area Network (WAN) – consists of several
smaller networks
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5 LAN Standards
LAN technologies are standardized by the
Institute of Electrical and Electronics
Engineers (IEEE) Project 802 – Local
Network Standards
– IEEE 802.3 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
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5 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?
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5 Network Devices
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5 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)
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5 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?
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5
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)
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5 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
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5 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)
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5 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)
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5 Ethernet Frame Structure
Type
IEEE 802.3 Ethernet frame
64 – 1518 bytes in length
 Preamble: 8 bytes
 7 bytes with pattern 10101010, followed by one byte with pattern
10101011 (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
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5 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?
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5 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
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5 QuickCheck page 207/255
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5
SECTION
B
Wired Networks
Wired Network Basics
HomePNA and Powerline Networks
Ethernet
Ethernet Equipment
Ethernet Setup
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5 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
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5 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
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5 Ethernet
Simultaneously broadcasts data packets to
all network devices (a star topology)
– IEEE 802.3 defines the Ethernet protocol
– CSMA/CD protocol used to share the channel
Vary in speed from 10Mbps to 10Gbps
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5 EthernetOn 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.
CSMA-Carrier Sense Multiple Access with Collision Detection
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5 Ethernet Equipment
Checking a workstation
for an Ethernet port
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5 Ethernet Equipment
Ethernet adapter - NIC (designed to support
the Ethernet protocols)
Network hub
Network switch
Network router
RJ45 connector
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5 Typical Ethernet Setup
Technically, this
device functions as
an Ethernet switch,
as well as an IP
router.
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5 Quickcheck 216/264
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5
SECTION
C
Wireless Networks
Wireless Basics
Bluetooth
Wi-Fi
Wi-Fi Equipment
Wi-Fi Setup
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5 Wireless Basics
 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
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5 Most popular technologies
Wi-Fi
Bluetooth
WiMAX
– Fixed internet access
Zigbee
– Internet of things
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5 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
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5 Wi-Fi
Wireless networking technologies that are
compatible with Ethernet (per IEEE 802.11)
MIMO technology uses two or more
antennae to send multiple sets of signals
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5 Wi-Fi Equipment
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5 Wi-Fi Equipment
If your computer is not pre-equipped with
wireless circuitry, you can purchase and
install a Wi-Fi card
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5 Wi-Fi Equipment
Wireless network setups
– Wireless ad-hoc network
– Wireless infrastructure network
• Wireless
access point
• Wireless
router
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5 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
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5 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)
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5 Typical Wi-Fi Setup
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5 Quick 225/273
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SECTION
D
Using LANs
LAN Advantages and Challenges
Sharing Files
Sharing Printers
LAN Parties
Troubleshooting
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5 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”)
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5
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5 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
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5 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
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5 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.
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5 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)
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5 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.
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5 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
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5 Sharing Printers
In Windows, use the Printers and Faxes
dialog box to allow other users to share the
printer attached to your workstation
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5 P233/281
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5
SECTION
E
Security Through Encryption
Wi-Fi Security
Encryption
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5 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
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5 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
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5 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
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5 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
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5 Encryption
Public key encryption (PKE) eliminates keydistribution problem, by using one key to
encrypt a message and another key to
decrypt the message
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5 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:
Unlocking key
– Send me the locked box.
Locking key
– Buy a strong box
– Use my lock with the
locking key to lock the
letter inside.
5
Encryption with a Public Key System
Bob
(ke , kd ) is the key pair
of Alice
encryted
file
file
m
Alice
Alice’s
public
Key ke
E k (m)
e
file
Alice’s
Private
Key kd
m
5
Digital Signature with a public key
system
Bob
Alice
(ke , kd ) is Bob’s
key pair
m
m
m||Dk (f(m))
d
f
f(m)
Dk (f(m))
d
f(m)
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Key Exchange with a Public Key System
Bob
(k e , k d ) is the key pair
of Alice
session
key
k
Alice
encryted
sess. key
Alice’s
public
Key ke
E k (k)
e
Alice’s
Private
Key kd
session
key
k
Bob generates the session key k, sends Alice the encrypted session key.
Basic Computer Application
Chapter 5 Complete
LANs and WLANs