Transcript IT 141: Information Systems I

Tonga Institute of Higher Education
IT 141: Information Systems
Lecture 7
LANS & WLANS
Encoding and Decoding
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The data has to be encoded before
being sent.
For computers, this means they
must be encoded into binary.
We have already seen one type of
encoding, it is called ASCII.
Characters are encoded into binary
in ASCII
NETWORK CLASSIFICATIONS
- 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. – I EEE 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 are
configured with Ethernet technology and use
compatible Wi-Fi standards in applications that
require wireless access.
Network Devices
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1. node – A single device connected to a network is
called a node
2. Modem – uses phone lines to transmit data over a
network
3. Network Interface Card (NIC) – a peripheral to
connect to a local area network with Ethernet cable.
4. Hub/Switch – a device that connects nodes on a
network together (hub slow, switch fast)
5. Router – connects two different networks
together (like a local network and the internet)
6. Repeater – amplifies signals on a network so that
they don’t lose data to noise
7. Network-attached storage (NAS) – a storage
device that directly connects to a network
Network Devices
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8. 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
 Print server – handles jobs sent to network printers
Can a network function without a server? – yes. Files
and applications can be shared among workstation
operating in PEER-TO-PEER MODE. They can use
popular file sharing systems such as Gnutella, Kazaa and
BitTorrent to operate in peer to peer mode.
Network Devices
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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
Network Physical Topology
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physical topology is the arrangement of devices in a network
1) Star topology 2) Bus topology 3) Ring 4) Mesh 5)Tree
topology
1. Star topology – a disadvantage with wireless networks. Advantage is
if any link fail, it doesn’t affect the rest of network
2. Ring topology – minimizes cabling but failure of one device can take
down the whole network
3. Bus topology – work best with a limited number of devices. If
backbone cable fails, the entire network becomes useless
4. Mesh topology – Advantage: if several links fail, data can follow
alternative functioning links to reach destination. Used for wireless.
5. Tree topology – blend of star and bus networks. Excellent flexibility
for expansion. Many of today’s school and business networks are based on
tree topologies.
Bridge – a device that can connect two similar networks
Gateway – any device or software code used to join two
networks, even if those networks use different protocols or
address ranges
Network Links
What connects the nodes of a network?
 “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)
Bandwidth
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Bandwidth the word describe 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)
If the network is slow your "bandwidth" is small. To
get a faster speed you may need to purchase a
higher speed to obtain more bandwidth.
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)
Communications Protocol
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Protocol – a set of rules for interacting and negotiating.
Communications protocol – set of rules for efficiently
transmitting data from one network node to another
(process called handshaking)
Commonly used to describe how computers send data
over a network link
Protocols are responsible for the following aspects of
network communications:
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Dividing messages into packets
Attaching addresses to packets
Initiating transmission
Regulating the flow of data
Checking for transmission errors
Acknowledging receipt of transmitted data
TCP/IP and Network Protocols
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The most popular communications protocol is called
TCP/IP (transmission control protocol / Internet protocol)
It is used for transferring websites and email because it is
able to safely send data without error.
All computers that use TCP/IP know how to communicate
with each other, even if they use different operating
systems or are located in different countries.
All modern networks use TCP/IP to transmit most data.
Other protocols commonly used are
 UDP – for sending data quickly without checking for
errors
 ICMP – for checking connections between computers
How is data sent through a network
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When data is transmitted (sent) it is
usually sent by electromagnetic signals
This means the data will take different
forms depending on the transmitter and
receiver. For example, electronic
voltages, radio waves, light waves or
phone tones.
To get the Internet in Tonga, think about
all the different connections.
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Ethernet cables, satellites, underwater cables,
phone lines
Sending Data
How does data travel over a network?
- 1948, Claude Shannon published an article describing
the communications system model applicable to
networks of all types including today’s computer
networks
- Data transmitted over a network usually takes the form
of an electromagnetic signal. Digital signals are
transmitted as bits using limited set of frequencies.
Analog signals can assume any value within a specified
range of frequencies
- What about corrupted signals?
- Correcting errors is one of the responsibilities of protocols
Packets
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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.
Circuit switching
Packet switching
Why packets?
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Why break up data into small parts?
When people designed networks, they
realized if data pieces were smaller it
would be easier to manage. If one packet
was lost it could be easily resent.
If a big file was sent all at once and there
was an error in the data, you’d have to
send the whole big data file again
With packets you just send small little
pieces of data
Network Addresses
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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.
Address:
 Physical Address (network address, MAC
address)
 Logical Address (IP address)
 Domain Name
How do devices get a network
address
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MAC addresses: Unique number assigned to a network
interface card when it is made. Used for network security
IP addresses: a series of numbers used to identify a network
device. (e.g. 204.127.129.1) It is separated into 4 sections by
periods. Each section is called an octet, because in binary it is
represented by 8 bits.
 It can be assigned by ISPs or system managers. 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)
Dynamic and Static IPs
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If your IP address does not ever change, it is
static.
Usually servers and websites will have static
IP addresses because other computers
always need to know where to find them
A dynamic IP address will change every time
you connect to the internet. Usually, if you
connect to the internet through a modem,
you will have a dynamic IP
If you have a dynamic IP, you can’t have a
server on your computer
Physical Addresses
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A physical address is built into the
hardware of a network interface
card (NIC). This address may also
be called the MAC address.
Every NIC has a unique physical
address. No other device will share
the same address.
The Logical Address - IP Addresses
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Besides the physical address, a computer needs a
logical address that is used by the operating
system and software in order to connect to other
computers.
IP addresses are the way that computers know
where to send data. Every computer on a network
has a different IP address
The IP address is a series of numbers like
192.168.0.2
Each number can range from 0-255, which means
each part is 8 bits (2^8 = 256). Since there are 4
parts, each IP address uses 32 bits.
How many IP addresses can be used on the
internet? Just over 4 billion.
Domain Names
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Computers may be able to remember and
use IP addresses easily, but people have
trouble remembering long numbers
Domain names were invented so people have
an easier time remembering the location of a
server
A domain name will “map” an IP address to a
name
Our domain name is tihe.org and our IP
address is 209.58.72.33.
Domain names will end in an extension that
indicates something called the ‘top-level’
domain.
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Example: .org, .to., .net
Wired Networks
Wired network – 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 –
Powerline network – uses premises electrical wiring to
form the infrastructure for a LAN
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ETHERNET: Wired Link
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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].
 It takes care 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
EHTERNET EQUIPMENT
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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
Routers
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Routers are similar to hubs in
that they connect networks
together, but routers are used to
connect different networks
together.
Most of the time, you will use a
router to connect your network to
the Internet.
It is a special device that
determines where the data
should go on your network.
Either to the internet (or another
network) or stay inside your LAN
ROUTER
HUB
Types of Links/Cables
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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
Wireless Networks/Cable-less
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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
Wireless networks
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Advantages
 Mobility
 No unsightly cables
 Power spikes are much less likely to run through
cables to damage workstations
Disadvantages
 Was more expensive in the past
 Speed
 Range
 Licensing
 security
POPULAR TECHNOLOGY FOR
WIRELESS NETWORKS
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Wi-fi
Bluetooch
Wireless USB (WUSB)
Wireless HD (WiHD)
Bluetooth
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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
Wi-Fi
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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