Transcript Wireless Topology

WIRELESS LAN & PDA
CIS 454 (LAN)
Prof. Ganesan
Group members & outline
• Belinda
– Wireless LAN
• Anthony Vu
– Topology & wireless technology of LAN
• Ka Yan (Susana) Chung
– Implementation of wireless LAN
• Norman-Ngan Vu Lam
– Personal Digital Assistant (PDA)
WIRELESS LAN
WIRLESS LOCAL AREA
NETWORK
INTRODUCTION
• It is a flexible data communications system
implemented as an extension to, or as an
alternative for, a wired LAN.
• Using radio frequency (RF) technology, wireless
LANs transmit and receive data over the air,
minimizing the need for wired connections.
• With wireless LANs, users can access shared
information without looking for a place to plug in,
and network managers can set up or augment
network without installing or moving wires.
WHY WIRELESS?
Wireless LANs offer the following
Productivity, convenience, and cost advantages over
traditional wired networks:
• MOBILITY
• INSTALLATION SPEED AND SIMPLICITY.
• INSTALLATION FLEXIBILITY.
• REDUCED COST-OF-OWNERSHIP.
• SCALABILITY.
MOBILITY
Wireless LAN systems can provide LAN
users with access to real-time information
anywhere at work and in the home.
INSTALLATION SPEED AND
SIMPLICITY
Installing a wireless LAN system can be fast
and easy and can eliminate the need to pull
cable through walls and ceilings.
INSTALLATION FLEXIBLITY
Wireless technology allows the network to go
where wire cannot go.
REDUCED COST-OFOWNERSHIP
While the initial investment required for
wireless LAN hardware can be higher than
the cost of wired LAN hardware, overall
installation expenses and life-cycle costs
can be significantly lower. Long-term cost
and benefits are greatest in dynamic
environments requiring frequent moves and
changes.
SCALABILITY
Wireless LAN systems can be configured in a variety
of topologies to meet the needs of specific
applications and installations. Configurations are
easily changed and range from peer-to-peer
networks suitable for a small number of users to
full infrastructure networks for thousands of users
that enable roaming over a broad area.
OVERVIEW BY INDUSTRY
• Currently wireless LAN is not a replacement for
the wired infrastructure, but it is a significant
complement to what currently exists. Some
examples in the industry are:
–
–
–
–
–
EDUCATION.
MANFACTURING COMPANIES.
HEALTHCARE.
RETAIL.
FINANCIAL/OFFICE-AUTOMATION.
MAJOR FINDINGS IN THE
INDUSTRIES
• 89% Of the companies experienced a successful
implementation.
• 92% of respondents interviewed believe there is a
definite economic and business benefit after
installation.
• 92% of respondents reported that they will
continue to deploy wireless technology in their
network through 2000 because of the benefits
experienced by end users and/or IT staff.
• Payback was less than one year, across all
industries surveyed.
Cost Chart
RETAIL
MANUFACTURING
HEALTHCARE
OFFICE
AUTOMATION
EDUCATION
Benefits per
Company
(millions $)
5.6
2.2
.94
2.5
.5
Costs per
Company
(millions $)
4.2
1.3
.90
1.3
.3
9.7
7.2
11.4
6.3
7.1
Payback
(#of months)
Wireless Topology
• Topologies are architectural drawings representing
the cable layout for the wireless LAN.
• Topologies of a network are the physical
configuration of the nodes in the network.
• They can be hardware dependent.
Topologies
Star Topology (Centralized)
• Star topology is probably the oldest topology used
for data communication.
Star Topology (cont)
• Computers are connected through a series of
point-to-point dedicated circuits.
• Each computer is linked by a separate full-duplex
point-to-point through the central computer.
• It is easy to set up.
Bus Topology
• Star topology is sometimes known as the linearbus topology.
• All terminals share a single cable to transmit and
receive messages.
• There are endpoints to cable segment commonly
known as terminating points.
Physical Bus Topology
Ring Topology
• In the ring topology, all computers are connected in
a close loop.
• Each computer links to the next one.
• There is no endpoints to this cable topology.
• Messages can travel around the ring in one
direction.
Physical Ring Topology
Speed and Distance
• Transmission speed worsens problems
– Error rates increase because bit periods are smaller and are
more likely to be damaged by brief noise spikes and
interference.
– High speeds create high-frequency components in the
signal that attenuate more rapidly than lower-frequency
components.
– In general, as speed increases, maximum distance
decreases, although improving technology can lessen the
decrease.
Applications According to Electromagnetic
Spectrum
How cellular phone works ? (cont.)
This process takes the
same amount of time
that it takes to make a
call from a landline
phone.
Solid Objects
Between Office Buildings
How Does Satellite Work?
• Communication
• Frequency
• Uplink & downlink
Between Ground Unit and
Satellite
Attenuation
• As signal travels, gets weaker
– If too weak, cannot tell 1s and 0s
Distance
Distortion
• As signal travels, it become distorted
– Changes shape
– Successive bits may merge, making reception
difficult
Distance
Noise
• Unwanted energy on line. Always present
• Noise floor is average level
• Noise spikes will cause problems
Signal
Strength
Signal
Noise
Spike
Noise Floor
Time
Approaching the Noise Floor
• Attenuation will bring signal ever closer to
the noise floor, creating more errors
Signal
Strength
Signal
Noise Floor
Distance
Interference
• Unwanted signal from outside sources
– Often intermittent, difficult to diagnose
Signal
Strength
Signal
Interference
Implementation of Wireless LAN
by Susana
Wired Vs. Wireless LAN.
• Wired LAN transmit
data in cables such as
twisted pair, coaxial,
and fiber optic cable.
• Wireless LAN
transmit data in air, it
use infrared (IR) or
radio frequency (RF)
to transmit data on air.
Radio Frequency (RF)
• Microwave transmission high frequency, narrow band
radio waves that require
special license.
• Spread spectrum - spread
signal over a range of
frequency, therefore, harder
to intercept
• RF electromagnetic wave can easily pass through ordinary
wall, it needs to implement with heavy concrete or metal
screening.
Infrared (IR)
• Indoor infrared is the most secure
wireless LAN, it’s the easiest
types of wireless signal to contain
with a certain location. Also, no
license needed.
• Use to connect nodes over small
distance.
• Point-to-point infrared must be within sight of each other
with no obstacles in the path of signal.
• Signal would be weaken by moist environment, dusty
environment, person in signal path, and sheet of plastic.
Wireless LAN Hardware
Implementation
• A wireless NIC - connect nodes to transmission
medium. Allow communication between node and
network. Consist of on board transceiver, & fix/external
antenna.
• For PC, wireless NIC are either PCI/ISA, for laptop, it
uses PCMCIA type II card.
• Installs driver to configure NIC.
• Another option of wireless LAN implementation is
“wireless LAN adapter” - external desktop transceiver
and antenna connect to PC through parallel port and it
function like a NIC.
Wire Replacement System
• It use wireless transmission instead of cabling to
communicate with backbone.
• Make use of existing Ethernet .
• Use device called “user modules and control modules.”
• User module is a desktop transceiver and antenna can
be shared with up to 8 nodes with Ethernet cards that
are individually wired to the user module.
• Control modules are similar to AP, it allow
communication with wired backbone through control
modules.
Data-link Layer
• Data-link layer of the OSI model governs
a node’s access to a shared medium.
• Logical link control (LLC) layer deal
with communication between nodes over
a single link of network.
• Media access control (MAC) layer which
define how user obtain access to the
shared medium when they need it.
“OSI 7 layers”
Different Types of MAC
•Random Access MAC
•Ordered MAC
•Deterministic MAC
Random Access MAC
•
•
•
•
Simple to implement
Offer fast response time under light network traffic
Offer effective throughput under heavy traffic
Wired network use CSMA/CD protocol to ensure data
transmit efficiently (it checks if line is free, then transmits
and listen if there’s collision, if collision, it stops and waits
for re-send)
• Wireless NICs can’t transmit and receive on the same
frequency at the same time, therefore, it can’t detect
collisions.
Random Access MAC (continue)
• Wireless NIC might not aware of all other node on network known as “hidden node” (a node outside of coverage area)
Wireless network use CSMA/CA - Carrier sense multiply
access with collision avoidance. Also known as LBT - Listen
before you talk. (Check if line I free, if yes, send and wait for
acknowledgment for receiving node, if no acknowledgement
receive within set period of time, it assume a collision occur
and wait to re-send)
• CSMA/CA can’t be use when there’s hidden node
• CSMA/CA cam be adapted to use with hidden node with the
use of RTS/CTS/ACK - request to send/clear to
send/acknowledge.
Ordered MAC
• Ordered MAC is unsuitable for wireless
LAN because it is possible for a node to
leave the bus or ring and break the orders
Deterministic MAC (3 types)
1) Time division multiple access (TDMA) - each node given the same set
amount of time to transmit data.
-Another type of TDMA is reservation/polling MAC - node sends
request to control point to request channel, channels are issue on a
“first come first serve” base.
2) Frequency division multiple access (FDMA) - available bandwidth is
divide into channels of different frequency and nodes allocate a
particular frequency.
3) Code division multiple access (CDMA) - nodes share same channel
bandwidth but use different spreading code to prevent interference.
Deterministic MAC (continue)
• Deterministic MAC provide effective throughout and response
time when network traffic is heavy.
• Each node must request access from control point before
transmitting, therefore, deterministic MAC have slower response
time than Random Access MACs in light traffic conditions.
CSMA/TDMA
• Combination of random-access MAC and
deterministic MAC technique is called
CSMA/TDMA. It offers fast response time
in light traffic; effective throughout under
heavy, but more complexes to administer on
the network
• CSMA/CA, RTS/CTS/ACK and
CSMA/TDMS are suitable for wireless
networks.
Access Point (AP)
Access Point are consists of
1) A wired NIC to communicate with wired
backbone
2) A transceiver and antenna to communicate
with wireless node within range
3) MAC-layer bridging software.
• AP can be use to extend the range of a
wireless network or connect an existing wired
LAN to a wireless LAN.
• Wireless subnets are connected to a wired backbone through AP.
• AP bridging ensure only packet destined for wireless nodes within its
service are forwarded to the wireless subnet.
Bridging
• Bridging - device that filters traffic
between different section of the same
network, of different LAN
• It acts like a repeater, & sends data to
both wired and wireless network.
1) Bridging software processes data and analyzes address info on packet.
2) It construct a table indicate location of each node.
3) Each time it receives packet, it checks if destination address is in table
4) If address to wired LAN, it checks if on table, if yes, only forward to
wired LAN, if not, it forward to both wired and wireless.
Bridging (continue)
• There are 2 ways to create table
1) Source route algorithm - entire path of the package is included in
each frame and bridge record information, most of the routing
work is performed by nodes.
2) Spanning tree algorithm - used by most network, bridge notes the
direction from which it receives each packet and concludes source
node can be reach by sending packet in that direction and record it
in table. It regularly exchange configuration message with other
bridge, if one fails, network can adjust routing accordingly.
• Bridge-to-bridge protocol ensures each network section can only
access through a designated bridge.
• Table is not permanent. For wired LAN, entries “age out” in
hours; in wireless LAN, entries “age out” in minutes.
Mobile IP
• Wired node’s IP address associate with a particular physical
location; wireless node is addressed by a protocol called
Mobile IP.
• Mobile IP allows nodes to take an IP address with them when
they move.
• Wireless node using mobile IP is known as a mobile host.
• Mobile host can have 2 IP address at a time, one is home
address which is permanent; the other is “care of” address
which is temporary.
• Foreign agents provide mobile host with “care of” address and
home agents redirect package from home network to “care of”
address.
Security
• Encryption is an effective security technique, there are 2 types
of encryption technique.
1) DES chip - is a symmetric encryption method, use same
key for encrypting and decrypting.
2) RSA - is an asymmetric encryption method, use
different key encode and decode. Data is encoded
using public encryption key, and decoded using
private key.
• Symmetric encryption is faster than asymmetric, but possible
security risk.
• Only encrypting sensitive message at higher application level
before transmitting can reduce processing time.
PERSONAL DIGITAL
ASSISTANT
(PDA)
By
Norman-Ngan Vu Lam
What is PDA?
• Personal Digital Assistant
• A handheld PC that is capable of handling
all the normal task of the organizer and
more.
Features of PDA
• All Palm organizers include the following features:
– Applications: Date Book, Address Book, To Do List, Memo
Pad, Expense, Calculator, desktop e-mail connectivity,
Security, Games, and HotSync software for local and remote
synchronization
– Modem-enabled and Internet-ready with TCP/IP software
– An infrared port
– Windows and Macintosh compatibility**
Palm VII
• Check stock quotes from
the airport. Send e-mail
from a taxi. Book a flight,
get directions and read
the news virtually
anywhere, anytime.
• Wireless
Features of Palm VII
•
•
•
•
•
AAA bateries
Data transfer rate at 8kbps
2 MB of RAM
Web clipping
Palm Query Application (PQA)
Web Clipping Apps
•
Financial
–
–
–
•
News
–
–
–
•
ABCNEWS.com
ESPN.com
USATODAY.com
Reference and Directory
–
–
–
•
Bank of America
Fidelity Investments
E*Trade
Merriam-Webster
US WEST Dex
Yahoo! People Search
Travel and Entertainment
–
–
–
MapQuest.com
Moviefone.com
The Weather Channel
iMessenger
• Receiving messages
– Through your [email protected] account
– Only first 500 characters are being sent
• Sending messages
– There are 3 ways to compose text to send.
3 ways to enter data
• Graffiti
– Only display lower case
• Onscreen keyboard
– Both lower and upper case
• Desktop keyboard
– Hotsync technology
Graffiti Characters
On screen keyboard
Area coverage for PDA
What’s new?
• Unlimited plan
• Download web
clipping apps at
http://www.palm.net/apps/
PDA service plan
Basic Plan
Expanded Plan
Volume Plan
Unlimited
Plan
Monthly service fee
$9.99
$24.99
$39.99
$44.99
Kilobytes included in your monthly
service fee
50KB1
150KB2
300KB
Unlimited
Service Plan Options
Sample monthly
usage4
Each additional kilobyte
One-time set-up fee
30 messages
20 stock quotes
10 sports scores
10 traffic reports
10 weather
updates
$.20
$9.99
90 messages
60 stock quotes
30 sports scores
30 traffic reports
30 weather
updates
$.20
$9.99
180 messages
120 stock quotes
60 sports scores
60 traffic reports
60 weather
updates
Unlimited
$.20
$0
$9.99
$9.99
Strengths and weaknesses
• Pros
– Webclipping PQA
– iMessaging
• Cons
– Coverage for wireless services too limited
– Only 2MB of storage space
– Expensive & monthly service charges too high
References
•
•
•
•
•
•
Shelly, Cashman, and Serwatka. “ Business Data Communications” International
Thomson Publishing, 1998.
Naugle, G Mathew. “ Local Area Networking” McGraw-Hill, Inc. New York, 1991.
FitzGerald, Jerry & Dennis, Allen. “Business Data Communications and Networking”.
John Wiley & Sons, Inc. New York, 1999.
Robinson, Teri. “ Mobile Computing” Micro Times. No 203, pg137-39. Feb 8, 2000.
www.blackbox.com
www.calstatela.edu/cbtweb/curicula/courses/lant01e/lant01e.htm
References
• www.palm.net
• www.palm.com
• Hudson, I.J. “Intranet Access In the Palm of your hand” TechWeb
www.techweb.com August 23, 1999
• The PC technology guide www.pctechguide.com/25mob2.htm