CSE5807 Wireless and Personal Area Networks. Peter Granville tel: 9903 2448...
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Transcript of CSE5807 Wireless and Personal Area Networks. Peter Granville tel: 9903 2448...
CSE5807
Wireless
and
Personal Area Networks
Peter Granville tel: 9903 2448 [email protected]
Textbook:
Wireless Communications and Networks
Stallings, Pearson Prentice-Hall 2E also 1E is okay
Topics to be covered( May be subject to change)
Week 1 Wireless Introduction and Applications
Week 2 Radio Communications Principles
Week 3 Access Technologies
Week 4 Cellular Networks
Week 5 Cellular Networks ctd...
Week 6 IEEE802.11 Introduction
Week 7 IEEE802.11 ctd...
Week 8 Bluetooth Technology
Week 9 Network_Management_Issues
Week 10 Wireless_Security
Week 11 VPN
Week 12 Selected_Topics_in_Wireless
Week 13 Revision
Assessment:
Exam 2 hour 50%
Assignment 1 Research Essay 25%
Reports 25%
10 Reports each worth 2.5% of final result
Introduction to Wireless LANs
APPLICATION
PRESENTATION
SESSION
TRANSPORT
NETWORK
DATA LINK
PHYSICAL
WLANs Operate at this portion of the OSI model
Infra-Red
• Infrared (IR) systems use very high frequencies, just below visible light in the electromagnetic spectrum (refer fig 4.1), to
carry data.
• Like light, IR cannot penetrate opaque objects; it is either directed (line-of-sight) or
diffuse technology.
Inexpensive directed systems provide very limited range (3 ft) and typically are used for Personal Area Networks but occasionally are used in specific WLAN applications.
High performance directed IR is impractical for mobile users and is therefore used only to
implement fixed subnetworks.
Diffuse (or reflective) IR WLAN systems do not require line-of-sight, but cells are limited to individual rooms.
Bluetooth
Bluetooth technology is a relatively new wireless personal area networking (WPAN) technology that has gained significant industry support and will coexist with most wireless LAN solutions.
The Bluetooth specification is for a 1 Mbps, small form-factor, low-cost radio solution that can provide links between mobile phones, mobile computers and other portable handheld devices and connectivity to the internet.
This technology, embedded in a wide range of devices to enable simple, spontaneous wireless connectivity is a complement to wireless LANs — which are designed to provide continuous connectivity via standard wired LAN features and functionality.
Current Radio LANs use a transmission technique called Spread Spectrum.
Instead of using the one narrow frequency range for transmitting data, in Spread Spectrum transmissions are over a range of frequencies at a time.
Radio LANs
Spread Spectrum
The basic idea is to modulate the signal so as to increase the bandwidth (spread the spectrum) of the signal to be transmitted
Advantages: Gain immunity from various kinds of noise and
multipath distortion Can be used for hiding and encrypting signals. Only a
recipient who knows the spreading code can recover the encode information
Allows several users to independently use the same bandwidth with little interference eg CDMA as used in cellular telephony
Systems use one of two techniques for communications –
Direct Sequence
Frequency Hopping
Spread Spectrum
• Refer fig 7.1, 7.6 Stallings
• Direct sequence is perhaps one of the most widely known and utilized spread spectrum systems and it is relatively simple to implement.
• A narrow band carrier is modulated by a (chip or spreading) code sequence.
• The carrier phase of the transmitted signal is abruptly changed
in accordance with this code sequence.
Direct Sequence Systems
The code sequence is generated by a pseudorandom generator that has a fixed length. After a given number of bits the code repeats itself exactly.
The speed of the code sequence is called the chipping rate, measured in chips per second (cps). For direct sequence, the amount of spreading is dependent upon the ratio of chips per bit of information.
At the receiver, the information is recovered by multiplying the signal with a locally generated replica of the code sequence.
• With frequency hopping systems, the signal is broadcast over a seemingly random series of radio frequencies, hopping from frequency to frequency at fixed intervals.
• A receiver, hopping between frequencies in synchronization with the transmitter, picks up the message.
• Would be eavesdroppers hear only unintelligible blips
• Attempts to jam the signal in one frequency succeed only at knocking out a few bits of it
Frequency Hopping Systems
Frequency Hopping Systems
Refer fig 7.2 Stallings 2E Typically, there are 2k carrier frequencies
forming 2k channels The transmitter operates on one channel at a
time for a fixed interval eg 300ms IEEE 802.11 wireless LAN
During that interval, some number of bits is transmitted using some encoding scheme
The sequence of channels used is dictated by a spreading code.
Both transmitter and receiver use the same code to tune into a sequence of channels
Components of Wireless (Radio) Lans
http://www.cisco.com
http://www.symbol.com/products/wireless/wireless_products_lit.html
Access Point (AP)Network connection point for wireless devices
Access Point (AP)Network connection point for wireless devices
Access point
Laptop computer
Hand held computer
IEEE802.11Wireless LANs operating at data rates of 1 or 2 Mbps and operating in the 2.4GHz band were defined in the original IEEE802.11 specification ratified in 1997.The specification was for a cable-free LAN at the Data link and Physical layers of the OSI model.
IEEE802.11bIn September 1999, an amendment to the original standard added 5.5 Mbps and 11 Mbps. IEEE802.11b was named Wi-Fi (TM of Wireless Ethernet Compatibility Alliance WECA).
Physical Layer Convergence Procedure PLCP
MAC
Physical Medium Dependent PMD
Reformats data into form suited to PMD sub-layer and monitors medium for traffic Controls transmission and reception of data through wireless medium
PHY
IEEE802.11b uses the Ethernet-like multiple-access with collision-avoidance (CSMA/CA) method
Ethernet proper is based on CSMA/CD, where CD stands for "collision-detection." Wireless LANs can't always detect a collision between two transmitting devices, so instead, it tries for collision-avoidance
IEEE802.11a
Released in 1999
Operates in the 5 GHz frequency range and offers the possibility of 6 to 54 Mbps
HiperLAN2 (European) has similar
capabilities.
IEEE802.11g
Operates in the 2.4 GHz frequency range and offers the possibility of up to 54 Mbps
Is interoperable with IEEE802.11b Access Points and NICs
Applications of the Technology
Examples:
Retail,Hospitality,Education and Corporate trainingManufacturing,Government,Flexible office and public space environments http://www.symbol.com/products/wireless/wireless_products_lit.html
Retail Promotional and training videos On-line music sampling Portable, graphic-rich gift registries Customer service initiatives such as self-checkout
http://www.symbol.com/products/wireless/wireless_products_lit.html
Hospitality
Real-time connections to enable curbside or remote check-in for hotel guests avoiding lines at the front desk
http://www.symbol.com/products/wireless/wireless_products_lit.html
High-speed Internet access for hotel guests
Convention center networking for trade shows and conferences
Support of multimedia presentations and video streaming for guest meeting and information services
http://www.symbol.com/products/wireless/wireless_products_lit.html
Education and Corporate Training
Temporary networks for mobile training programs
Streaming multimedia to support on-line lectures
Wireless Internet and e-mail access
Security initiatives
http://www.symbol.com/products/wireless/wireless_products_lit.html
Manufacturing
Real-time transfer of mechanical, flow and other graphic-rich files
Security initiatives
Manufacturing workstations where production line layouts are frequently changed
http://www.symbol.com/products/wireless/wireless_products_lit.html
Government
Temporary networks for disaster area and refugee center support, including transferring photos and other vital information
Crime and accident scene support
Security initiatives via wireless monitoring systems and remotely accessed cameras
http://www.symbol.com/products/wireless/wireless_products_lit.html
More Flexible Office and Public Space Environments
Temporary project team and ad-hoc networking
CAD/CAM file transfer for collaborative product development teams
Wireless e-mail, document and PowerPoint® transfer
http://www.symbol.com/products/wireless/wireless_products_lit.html
Cable-less video conferencing
Flexible customer visit center configuration
Wireless local area networking where wiring isn't possible, such as landmark buildings or sites with asbestos considerations
http://www.symbol.com/products/wireless/wireless_products_lit.html
Kiosks in malls, airports, museums and other spaces where interactive programs depend on high-speed remote data retrieval
http://www.symbol.com/products/wireless/wireless_products_lit.html
Interference Problems
Most of the wireless LAN systems at the moment operate in the 2.4GHz band.
This is also used by Bluetooth systems. Thus interaction between radio transmissions of the various technologies may result.
Also, other radio equipment may interfere with the reception of signals.
Security/Privacy Issues
Many of the wireless LANs in use today potentially suffer from one major difference with wired LANs –the data is freely accessible due it radio transmission
Two issues arise – data privacy and authentication
WEP – Wired Equivalent Privacy deals with both issues
Data is encrypted to prevent its use following inappropriate capture
Has weaknesses, eg lack of encryption key management in the protocol
WPA – WiFi Protected AccessTemporary alternative to WEP providing better security
IEEE802.11i – new standard providing high levels of security (due soon)
Use of authentication servers (e.g. RADIUS) is promoted
VPNs – Virtual Private Networks
Assuming that wireless connections are not secure, how can you –
a) Secure your transmissions, b) Control Access
VPNs can do both at the same time.
Problem: proprietary – need client specific to VPN server.