Transcript Tonga Institute of Higher Education IT 141

Tonga Institute of Higher Education
IT 141
Lecture 6: LANS and WLANS
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Network Classifications
• Classified according to size and geographic scope
- PAN (personal area network) – within a range of 30 feet (10
meters)
- NAN (neighborhood area network) – within a limited
geographical area, usually over several buildings
- LAN (local area network) – connects personal computers
within a very limited geographical area
- MAN (metropolitan area network) – public high-speed
network capable of voice and data transmission within a
range of about 80 km
- WAN (wide area network) – covers a large geographical area
usually consists of several smaller networks
We will focus on LAN because you are most likely to
encounter this type of network.
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LAN standards
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It ranges from simple households to large
businesses
LAN standards – LAN technologies are
standardized by the Institute of Electrical and
Electronic Engineers (IEEE). E.g. – IEEE 802.3
is sometimes used to refer to a network standard
in articles and advertisements
Popular LAN standards – ARCnet, Token Ring,
FDDI WERE POPULAR.
Today, most LANS configured with Ethernet
technology and use compatible Wi-Fi standards in
applications that require wireless access.
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NETWORK DEVICES
• node – A single device connected to a network
• Workstation – personal computers connected to
a network
• Modem – uses phone lines to transmit data over
a network
• Network Interface Card (NIC) – network circuitry
required to connect a computer to a LAN
• Networked peripheral – any device that has
network circuitry to directly connect to a network
• Network attached storage (NAS)- storage device
that directly connects to a network
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CLIENTS, SERVERS, AND PEERS
• Servers – a computer that provides services
for other computers on a network called
clients
E.g.
– Application server – run application
software for network workstations
– File server – stores files and supplies them
to workstations on request
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CLIENTS, SERVERS, AND PEERS
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Workgroup (Peer-to-Peer)
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A workgroup is a group of computer connected by a
LAN, but not sharing similar information, like
usernames and passwords.
This is commonly used in networks with less than five
computers where each user has their own computer
Domain (Client-Server)
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A domain allows all computers to be a part of a group
that shares usernames, passwords and various
settings.
This allows a user to log into any computer on a
network with the same password, as well as using the
same settings
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Interconnecting various networks
• Bridge – device that connects two similar
networks
• Gateways – device or software code used to
join two networks that use different
topologies. Term for any device or software to
join two networks, even if they use different
protocols or address range.
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NETWORK LINKS
• “communications channel” or link: physical
path or a frequency for signal transmissions
• Data in a network with wired links travels
from one device to another over CABLES (E.g.
– Ethernet, HomePNA, HomePlug)
• Networks without wires transport data
through the air or wireless network
technologies (E.g. – Wi-fi, Bluetooth)
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BANDWIDTH
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Bandwidth - how much data can be transmitted
over a network link over a certain amount of time
(transmission capacity of a communications
channel)
 E.g. Coaxial cable brings more than 100
channels of cable TV, and has a higher
bandwidth than your home telephone line.
56Kbps (dial-up), 10Mbps (cable TV), 100Mbps
(computer lab)
Network is slow your "bandwidth" is small. If
something has a lot of bandwidth it is called
broadband (Ethernet networks, cable TV)
If it has little bandwidth, it is called narrowband
(phone lines, infrared)
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COMMUNICATIONS PROTOCOLS
• Protocol – a set of rules for interacting and
negotiating.
• Communications protocol – set of rules for
efficiently transmitting data from one network
node to another
• Handshaking – process where a protocol helps
two network devices communicate
• TCP/IP – best known communications
protocol
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COMMUNICATIONS PROTOCOLS
• Protocols are responsible for the following
aspects of network communications:
– Dividing messages into packets
– Attaching addresses to packets
– Initiating transmission
– Regulating the flow of data
– Checking for transmission errors
– Acknowledging receipt of transmitted data
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DATA TRAVELLING OVER A NETWORK
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COMMUNICATIONS PROTOCOLS
• Digital signals are transmitted as bits using
limited set of frequencies
• Analog signals can assume any value within a
specified range of frequencies.
• Digital equipment is sensitive to only two
frequencies that represents 1s and 0s.
• If there are errors, protocols usually correct
these
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PACKETS
• Most communication protocols will divide data
into small pieces, called packets, when sending
over a network link
• Packets – parcel of data that is sent across a
computer network
• Each packet contains – address of its sender,
destination address, a sequence number, some
data. At destination, packets rearrange
themselves into original message according to
sequence numbers.
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SENDING MESSAGES
• Circuit switching – technology used by
communications networks, such as the
telephone system
• Packet switching – technology, which divides a
message into several packets that can be
routed independently to their destination.
Every packet has destination addresses that
communication protocols use
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ADDRESS
• Every node on a network has at least one
address so that other nodes know how to
send data to it.
• A node may have other addresses depending
on the protocols it uses.
• Two commonly used Addresses:
– Physical Address (network address, MAC address)
– Logical Address (IP address)
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IP ADDRESSES
• Assigned IP addresses are semi-permanent
and stay the same every time you boot your
computer. (Static IP addresses)
• It can also be obtained through DHCP
(Dynamic Host Configuration Protocol). This
protocol was designed to distribute IP
addresses automatically. The next time you
boot, you will be assigned with a different IP
address. (Dynamic IP addresses)
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Packets reaching destination
• Packets might not travel directly to their
destination. When it reaches its destination, it
is checked for errors one last time and then
the packets are reassembled into their original
configuration.
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WIRED NETWORKS
• Uses cables to connect devices.
• Advantages – fast, secure, simple to configure.
• Disadvantages – devices connected have limited
mobility. Running cables can be a problem with some
building codes. Drilling can also be a problem
• Examples– Ethernet, HomePNA, HomePlug
technologies
• Home PNA – uses telephone wires and coaxial cables
• Powerline network – uses premises electrical wiring to
form the infrastructure for a LAN
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ETHERNET
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Ethernet – simultaneously broadcasts data packets to all
network devices. A pack is accepted by the device to which
it is addressed
Ethernet relies on CSMA/CD [Carrier Sense Multiple Access
with Collision Detection].
 Takes care of network devices transmitting packets at
the same time
 It detects collision, deletes the colliding signals, resets
network and prepares to retransmit data
How fast? Original carried data over a coaxial cable bus
topology at 10 Mbps. Today, up to 40 or 100 Gbps
Ethernet is popular because it is easy to understand,
available almost everywhere, allows flexibility in network,
and compatible with Wi-Fi networks
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ETHERNET EQUIPMENT
• Two or more Ethernet-ready computers (look for an
Ethernet port, and determine it’s speed. If the
computer doesn’t have one, install an Ethernet
adapter, or Ethernet card/NIC)
• An Ethernet router (hub – device that links two or
more nodes of a wired network. Switch – sends data
only to the devices specified as the destination. Router
– ship data from one network to another)
• Surge strip or UPS
• Network Cables for each computer
• Internet access device such as cable modem or DSL
modem and corresponding cables
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NETWORK DEVICES
• Network device/appliance – electronic device
that broadcasts network data, boosts signals,
or routes data to its destination
• Hub/Switch – a device that connects nodes on
a network together (hub slow, switch fast)
• Router – connects two different networks
together (like a local network and the
internet)
• Repeater – amplifies signals on a network so
that they don’t lose data to noise
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Types of Links/Cables
Twisted Pair cable – 4 copper wires twisted
around each other. These are what are used for
phone lines and Ethernet cables. They will end in
a RJ-45 plug for Ethernet, or RJ-11 for a phone
line
Coax Cable – one wire that is surrounded by
insulators to reduce data loss. Used for cable
television and modems sometimes
Fiber optic – A bundle of extremely small glass
tubes. They do not use electric signals like the
other cables, but use lasers instead. They are
very fast and expensive
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Wireless Networks/Cable-less
• Does not use cables or wires
• USES
• 1. Radio – Uses what is called RF signals (radio waves). Sent
and received with a transceiver (a transmitter and receiver
combined)
• 2. Microwaves – These can carry a lot of data, but need a
direct line of sight to work well
• Because radio and micro waves cannot bend to go around the
curve of the earth, satellites are used in space to transmit
signals around the globe
• 3. Infrared light – uses light waves to transmit data. Only good
for very short distances with clear line of sight
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Wireless networks
• Advantages
– Mobility
– No unsightly cables
– Power spikes are much less likely to run through
cables to damage workstations
• Disadvantages
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Was more expensive in the past
Speed
Range
Licensing
security
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POPULAR TECHNOLOGY FOR WIRELESS
NETWORKS
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Wi-Fi
Bluetooth
Wireless USB (WUSB)
Wireless HD (WiHD)
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Bluetooth
• Short-range wireless network technology
• Bluetooth networks automatically forms when two or
more Bluetooth devices come within range of each other.
• Piconet – a Bluetooth network
• Operates at the unlicensed 2.4GHz frequency
• Not for a collection of workstation but for mouse,
keyboard or printer to computer connection
• For PAN
• Speed: Bluetooth 2.1 – 3 Mbps, range of 3 to 3000 feet.
Bluetooth 3 – operates in the 6 to 9 GHz frequency
range, peak speeds of 480 Mbps
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Wi-Fi
• Set of wireless networking technologies
defined by IEEE 802.11 standards that are
COMPATIBLE with Ethernet.
• Transmits data as radio waves over 2.4 GHz or
5.8 GHz frequencies
• Speed and range can be improved with
various technologies including MIMO
(multiple-input multiple-output)
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Wi-Fi Standards
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WIRELESS SETUP
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WIRELESS SETUP
• Check the computer’s if it has wireless
capability
• If not, you can add a Wi-Fi adapter and plug it
into a PC slot or USB port
• Wireless ad-hoc network: devices broadcasts
directly to each other
• Wireless infrastructure network: there a
wireless access point (wireless router)
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WIRELESS SETUP
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Set up the router
Connec to the router with a computer
Configure router
Access the router setup utility
Create a new router password
Enter a SSID for the network
Activate WEP, WPA or PSK and create and
encryption key
• Set up the wireless workstations
• Connect an Internet access device
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Security through Encryption
• LAN jacking – hackers interception signals
driving through wireless enabled premises
• Pinpoint wireless access point
• Can see hackers in the list of clients accessing
your network
• Preventing interception is difficult, but
encrypting makes data useless to intruders
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WIRELESS ENCRYPTION
• WEP (Wired Equivalent Privacy)
• WPA (Wi-Fi Protected Access), WPA2 making
sure that packets have not been intercepted .
PSK (pre-shared key) a type of WPA, and PSK2
• To activate, use the router configuration
utiliteis to select and encryption protocol, and
create a wireless network key
• Basis for scrambling and unscrambling. Key is
similar to password.
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ENCRYPTION
- Transforms a message in such a way that its
content are hidden from unauthorized readers
- Can be used to
- Scramble data over wired or wireless networks to
prevent intrusions
- Security credit card numbers and other personal
information transferred from shoppers’ computers to
e-commerce sites
- Encrypting computer databases
- Scrambling email contents to maintain privacy
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How encryption works
• Original message (plaintext/cleartext) Is
encrypted to ciphertext. Converting ciphertext
to plaintext is decryption.
• Uses cryptographic algorithm and key
• Cryptographic algorithm: way for encrypting
or decrypting a message
• Eg. Do not trust Brutus (see next slide)
encrypted to GRQRWWUXVWEUXWXV
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ENCRYPTION
The algorithm for Caeser’s encryption technique
was to offset letters of the alphabet.
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Weak & Strong encryption
• Weak encryption: Caeser’s simple substitution key
• Strong encryption: very difficult to break
– E.g. Advanced Encryption Standard (AES) used for WPA2
• Breaking encryption methods uses expensive,
specialized, code-breaking computers
• 32-bit key, 4.2 billion numbers, 40-bit key, 1 trillion
numbers.
• There is 56-bit and 64-bit
• 128-bit and 256-bit takes a long time to decrypt
• Most encryption uses 128-bit
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Public key encryption
• Symmetic key encryption: KEY used to encrypt
a message is also used to decrypt
• Public key encryption: uses one KEY to encrypt
a message, but ANOTHER KEY to decrypt the
message
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Public Key encryption
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