Wireless Networks

1
Wireless Networks

• Supervised by
• Dr. Hasan Abbas
• Presented by
• E. Fadi Hasan

2
Why Wireless?

• Extension of wired LAN
• Alternative for a wired LAN
• Ease of installation
• Mobile users
• Scalability

3
Types of 802.11

• 802.11 Infrared
• 802.11 FHSS (frequency hopping spread spectrum)
• 802.11 DSSS (direct sequence spread spectrum)
• 802.11b HR-DSSS (HR high rate)
• 802.11a OFDM (orthogonal frequency division
  multiplexing)

4
Network architecture (1)

• Basically, WLAN network consists of four
  components Distribution System, Access Point,
  Mobile Station, and wireless medium.
• Distribution System (DS)
• - A backbone network that connects several
  access points or Basic Service Sets.
• - Wired or wireless, implemented
  independently.
• - In general, Ethernet is used as the
  backbone network technology.

5
Network architecture (2)

• Access Point (AP)
• - Connected to the DS, wireless-to-wired
  bridging function.
• Mobile Station (MS)
• - In general, its referred to laptop
  computer.
• Wireless medium
• - Frequency Hopping, Direct Sequence Spread
  Spectrum, Infra-red.

6
WLAN Applications

• Small Office Home Office (SOHO)
• Industrial, healthcare and educational facilities
• Building-to-Building(s) Connectivity
• Network Extension
• Temporary Networks and Hot Spots
• WISPs

7
SOHO Application
8
Industrial Application
9
Temporary/Movable Networks
10
Building-to-Building Connectivity
11
Network Extension
12
WISP
13
WLAN Configurations

• Independent WLAN
• Infrastructure WLAN

14
Independent WLAN

• Ad Hoc
• Simplest
• Rapid deployment
• Peer-to-peer
• No administration

15
Independent WLAN
16
Independent WLAN

• Can extended range by using an Access Point
  (acting as a repeater)

2d
17
Infrastructure WLAN

• Need an Access Point
• Connect to the wired LAN
• Need Infrastructure
• Need administration

18
Infrastructure WLAN
19
SOHO Infrastructure WLAN
Server
20
IEEE 802 .11 Terminology

• Access-Point (AP)
• Stations select an Access-Point and associate
  with it
• Access-Points
• Support roaming
• Provide time synchronization functions
  (beaconing)
• Provide Power Management support
• Traffic typically flows through Access-Point
• in IBSS direct Station-to-Station communication
  takes place

21
IEEE 802 .11 Terminology

• Basic Service Set (BSS)
• A set of stations controlled by a single
  Coordination Function (the logical function
  that determines when a station can transmit or
  receive)
• Similar to a cell in pre IEEE terminology
• A BSS can have an Access-Point (both in
  standalone networks and in building-wide
  configurations), or can run without and
  Access-Point (in standalone networks only)
• Diameter of the cell is app. twice the
  coverage-distance between two wireless stations

22
Basic Service Set (BSS)
BSS
23
IEEE 802 .11 Terminology

• Independent Basic Service Set (IBSS)
• A Basic Service Set (BSS) which forms a
  self-contained network in which no access to a
  Distribution System is available
• A IBSS without an Access-Point
• One of the stations in the IBSS can be configured
  to initiate the network and assume the
  Coordination Function
• Diameter of the cell determined by coverage
  distance between two wireless stations

24
Independent Basic Service Set (IBSS)
IBSS
25
IEEE 802 .11 Terminology

• Extended Service Set (ESS)
• A set of one or more Basic Service Sets
  interconnected by a Distribution System (DS)
• Traffic always flows via Access-Point
• Diameter of the cell is double the coverage
  distance between two wireless stations
• Distribution System (DS)
• A system to interconnect a set of Basic Service
  Sets
• Integrated A single Access-Point in a standalone
  network
• Wired Using cable to interconnect the
  Access-Points
• Wireless Using wireless to interconnect the
  Access-Points

26
Extended Service Set (ESS) single BSS (with
integrated DS)
BSS
27
Extended Service Set (ESS) BSSs with wired
Distribution System (DS)
BSS
Distribution System
BSS
28
Extended Service Set (ESS) BSSs and wireless
Distribution System (DS)
BSS
Distribution System
BSS
29
Frequency allocation channel arrangement

• RF refers to a portion of the electromagnetic
  spectrum in which radio waves can be generated
  and transmitted
• 802.11a, b and g standards use unlicensed radio
  frequencies (RF)
• 802.11 b g use the 2.4 GHz band with 3 non
  overlapping channels
• 802.11 a uses the 5 GHz band with 12 non
  overlapping channels
• Sender and receiver must be tuned in the SAME
  channel
• Receiver rejects signals on OTHER channels
• Channel arrangement for
  Channel arrangement
  for
• 802.11 b g networks
  802.11 a
  networks

30
Frequency Hopping Vs. Direct Sequence

• FH systems use a radio carrier that hops from
  frequency to frequency in a pattern known to both
  transmitter and receiver
• Easy to implement
• Resistance to noise
• Limited throughput (2-3 Mbps _at_ 2.4 GHz)
• DS systems use a carrier that remains fixed to a
  specific frequency band. The data signal is
  spread onto a much larger range of frequencies
  (at a much lower power level) using a specific
  encoding scheme.
• Much higher throughput than FH (11 Mbps)
• Better range
• Less resistant to noise (made up for by
  redundancy it transmits at least 10 fully
  redundant copies of the original signal at the
  same time)

31
802.11a 802.11g

• 802.11a is similar to 802.11b EXCEPT for
• Higher nominal data rates Up to 54 Mbps (20 Mbps
  in practice)
• Reduced range 50 meters max ? more APs are
  needed to cover the same area as for 802.11b ?
  Cost more to implement
• Different operating speeds 6, 9, 12, 18, 24, 36,
  48 and 54 Mbps
• 12 non-overlapping channels available
• Different transmission process
• 802.11g Now dominant standard
• Designed to combine advantages of 802.11b and
  802.11a
• Up to 11 Mbps for a range up to 150 m
• Up to 54 Mbps for a range up to 50 m
• Compatible with 802.11b
• 3 non-overlapping channels available
• Turbo mode Up to 108 Mbps (emerging standard)

32
802.11a Applications

• Building-to-building connections
• Video, audio applicationa
• Large file transfers, such as engineering CAD
  drawings
• Faster Web access and browsing
• High worker density or high throughput scenarios

33
802.11a
802.11b
2 Mbps
12 Mbps
5.5 Mbps
24 Mbps
36 Mbps
48 Mbps
11 Mbps
54 Mbps
34
802.11b should be considered if

• you do not intend to use high bandwidth
  applications.
• you need a wider coverage area.
• price is a primary consideration.
• 802.11b WLAN costs roughly a quarter as much as
  an 802.11a network covering the same area at the
  same data rate.

35
802.11a should be considered if

• you need to run higher-bandwidth applications
  such as voice or video.
• you have small densely packed concentrations of
  users
• The greater number of non-overlapping channels
  allows access points to be placed closer together
  without interference.

36
802.11g should be considered if

• you need to run higher-bandwidth
• applications and also need a wide coverage area.
• you need backward compatibility with 802.11b
  equipment.

37
MAC Services

• Synchronization
• Specifies the Timing Synchronization function
  (TCF)
• Within a BSS (quasi) periodic transmission of
  beacon signals contains timestamp all local
  nodes adjust their local timer according to the
  timestamp.

38
MAC Services

• Power management
• Two states for a station sleep and awake
• Transceiver is switched off whenever it is not
  needed
• Transceiver wakes up periodically and checks
  whether there are any data frames for it buffered

39
MAC Services

• Roaming
• Station starts scanning for a new access point if
  current link quality is very poor
• Passive scanning and Active scanning
• Selects best access point based on signal
  strength and sends Association request to it
• Selected AP informs DS which updates its database

40
MAC Services

• Scanning required for many functions
• finding and joining a network
• finding a new AP while roaming
• initializing an ad hoc network

41
Installing a Wireless LAN

• Survey the area
• Determine user and application requirements
• Design the WLAN
• Plan the installation
• Install the equipment
• Test the installation and Re-Survey

42
Survey the Area

• Purpose is to -
• Determine optimum installation locations
• Gain an appreciation of physical environment
• Document wiring connectivity limitations
• Identify Radio frequency interference
• Determine spacing required between APs

43
Determine the user and application requirements

• Data rate/throughput requirements
• Application (types) to be used.
• E.g. database, network, file etc.
• Number of users (esp concurrently)
• Operating hours, peak periods etc.
• Data security considerations

44
Design the WLAN

• Four main design Requirements
• High Availability
• - focus on redundancy, high roaming rates
• Scalability
• - focus on supporting multiple APs per coverage
  area
• Manageability
• - focus on remote management
• Interoperability
• - Focus on adherence to standards

45
Design the WLAN

• It involves
• Select topology and configuration
• Specing Wireless equipment
• - APs, antennas, wireless cards etc.
• Networking
• - subnetting, IP assignment, DNS etc.
• Select security model
• - authentication and encryption

46
WLAN Equipment

• Access Point(s) (APs)
• - connects the WLAN to wired network
• - point of network access for clients
• 2) Wireless Bridge(s)
• - connects two wired LAN segments
• - used in point-to-point or point-to-
• multipoint configurations

47
WLAN Equipment

• ) Antenna System
• - omni-directional provides a 360 deg radiation
  pattern
• e.g. dipole
• - directional directs signal mainly in one
  direction and less in all other directions
• e.g. yagi, patch and parabolic dishes

48
WLAN Equipment

• 4) Client Adapters
• - connects client device to the WLAN
• - PCMCIA for laptops/notebooks
• - Compact Flash (CF) for PDAs
• - PCI and USB for desktop PC
• 5) Lightning Arrestors
• 6) Power Injectors

49
Plan the installation

• Configure the wireless equipment
• - APs, wireless cards
• Prepare locations
• Ensure network connectivity for WLAN
  infrastructure devices
• Collect additional equipment and materials
• Develop installation strategy

50
Install the equipment

• Contact contractor
• Label all WLAN equipment
• - APs, copper, fiber etc.
• Mark location
• Install the WLAN equipment

51
Test the installation and Re-Survey

• Ensure that the requirements were met
• Intended area covered
• Bandwidth requirements met
• Security requirements met
• Troubleshoot Installation
• - hidden node, near/far, RF interference

52
Part (1)

• Wireless LAN Networks Design
• Site Survey or Propagation Modeling?

53
Abstract

• There are two basic ways to deploy wireless LAN
  access points in an indoor scenario
• manual deployment
• using a site survey .
• 2. Automatic planning .
• using a software tool .

54
Site Survey

• the main goal of a site survey is to
• measure enough information to determine
• the number and placement of access points that
  provides adequate coverage.

55
Propagation Modeling

• Software planning (using a propagation model) is
  
• much more convenient and cost-effective way .
• to deploy a wireless network than a site survey .
• with lots of measurements and empirical
  decisions.

56
Propagation Modeling

• There are two models
• 1. One-Slope Model .
• 2. Multi-Wall Model .

57
One-Slope Model

• The One-Slope Model (1SM) is the easiest way to
• compute the average signal level within a
• building without
• detailed knowledge of the building layout.

58
One-Slope Model

• The path loss in dB is
• function of just a distance between transmitter
  and receiver antennas
• where L0 (dB) is a reference loss value for the
  distance of 1 m,
• and d (m) is a distance.
• n is a path loss exponent .

59
Multi-Wall Model

• A semi-empirical Multi-Wall Model (MWM) provides
  much better accuracy than 1SM.

60
Multi-Wall Model

• The path loss between a transmitter and receiver
  LMW is given by .
• where LFSL (dB) is the free space loss for the
  distance d (m) .
• kwi is a number of walls .

61
Multi-Wall Model

• Lwi (dB) is attenuation factor .
• N is a number of wall types,
• kf is a number of floors
• and Lf (dB) is the floor attenuation factor.

62
Part (2)

• Coverage in WLAN
• Optimization Model

63
Abstract

• describe a mathematical model developed for
  finding the optimal location of AP .
• And find the transmitter power of AP .

64
Optimization Model and Algorithm

• We define
• Received points
  .
• Path loss from user to AP .
• Maximum tolerable path loss .

65
Optimization Model and Algorithm

• Step1
• find maximum path loss for AP placed in
• First position .
• Step2
• find maximum path loss for AP placed in
• second position .
• And so on for all considered positions .

66
Optimization Model and Algorithm

• Step3
• Search for minmum value of among
• Calculated path loss .
• Step4
• the position which mapping with minimum value is
  optimal position of AP .

67
Minimum transmitted power

• Transmitter power .
• Receiver threshold .

68
References

• Brian P Crow, Indra Widjaja, J G Kim, Prescott T
  Sakai. IEEE 802.11 Wireless Local Area Networks.
  IEEE Communications Magazine
• www.breezecom.com
• Jochen H. Schiller, Mobile Communications

69
References

• E. Anderson, K. Eustice, S. Markstrum, M. Hansen,
  P. L. Reiher , Mobile Contagion Simulation of
  Infection and Defense PADS 2005 80-87
• S. Capkun, J. P. Hubaux, and L. Buttyan "Mobility
  Helps Security in Ad Hoc Networks" Fourth ACM
  Symposium on Mobile Networking and Computing
  (MobiHoc), June 2003
• F. Castaneda, E.C. Sezer, J. Xu, WORM vs. WORM
  preliminary study of an active counter-attack
  mechanism, ACM workshop on Rapid malcode, 2004
• A. Chaintreau, P. Hui, J. Crowcroft, C. Diot, R.
  Gass and J. Scott, Impact of Human Mobility on
  the Design of Opportunistic Forwarding
  Algorithms IEEE INFOCOM, April 2006
• W. Hsu, A. Helmy, "On Nodal Encounter Patterns in
  Wireless LAN Traces", The 2nd IEEE Int.l Workshop
  on Wireless Network Measurement (WiNMee), April
  2006
• S.Tanachaiwiwat, A. Helmy, "Encounter-based
  Worms Analysis and Defense", IEEE Conference on
  Sensor and Ad Hoc Communications and Networks
  (SECON) 2006 Poster/Demo Session, VA, September
  2006
• A. Vahdat and D. Becker. Epidemic routing for
  partially connected ad hoc networks. Technical
  Report CS-2000.